' / 
 
 REESE LIBRARY 
 
 UNIVERSITY OF CALIFORNIA 
 
 Received 
 A c cessions No. *3 &&(> */ Shelf No. 
 
THE 
 
 BUILDING OF THE BRITISH ISLES. 
 
THE 
 
 BUILDING OF THE BKITISH ISLES 
 
 A STUDY 
 
 \ 
 
 IN 
 
 GEOGRAPHICAL EVOLUTION. 
 
 BY 
 
 A. J. JUKES-BROWNE, B.A., F.G.S., 
 
 OF THE GEOLOGICAL SURVEY OF ENGLAND AND WALKS J 
 
 AUTHOR OF THE " STUDENT'S HANDBOOK 
 
 OF GEOLOGY." 
 
 Illustrated by Maps and Woodcuts. 
 
 LONDON: OEOEGE BELL AND SONS, 
 YORK STREET, COVENT GARDEN. 
 
 1888. 
 
Vidi ego quod fuerat quondam solidissima tellus 
 Esse fretum. Vidi factas ex sequore terras. 
 
 OVJD, Metam. xv, 262. 
 
 oQ 
 
 CHISWICK PRESS : C. WHITTINGHAM AND CO., TOOKS COURT, 
 CHANCERY LANE. 
 
PREFACE. 
 
 THE object of this volume is the geological history of 
 the British Islands regarded from a geotectonic and 
 geographic point of view, that is to say, it does not deal 
 with the rock-groups of which our islands consist, so much 
 as with the physical conditions under which they were 
 formed, the rocks themselves being described only so far 
 as is necessary for ascertaining whence their component 
 materials were derived, in order to form some conception 
 of 'the relative position of land and water during each 
 of the successive periods of geological time. 
 
 The attempt made in a former volume on Historical 
 Geology to give brief accounts of the physical and geo- 
 graphical changes which took place during each period, 
 showed me that the subject required much more time and 
 consideration than I was then able to bestow upon it. 
 The restoration of the geography of any past period is a 
 problem of great difficulty, and the more remote that 
 period is from the present the greater does this difficulty 
 become. Most of the restorations given in the work re- 
 ferred to were very incomplete, and in the present state of 
 our knowledge many must remain so, but it seemed 
 possible that a more detailed consideration of the geo- 
 logical data, and a fuller discussion of the inferences de- 
 ducible from them, might yield better results, and might 
 at any rate pave the way for attaining to more complete 
 
VI PREFACE. 
 
 and accurate conceptions of the successive geographical 
 phases through which the British area has passed. 
 
 The pioneer in this branch of geological science was Mr, 
 Godwin- Austen, whose masterly essays published in the 
 " Quarterly Journal of the Geological Society," between 
 1856 and 1866, may still be read with advantage, for many 
 of his conclusions have been confirmed by the information 
 subsequently derived from deep borings in the eastern and 
 midland counties. 
 
 Many geologists have dealt in more or less detail with the 
 geographical conditions of particular epochs, but the first 
 systematic treatise on the geography of successive geo- 
 logical periods was that by Professor Hull, published in 
 1882, and entitled, "Contributions to the Physical History 
 of the British Isles." The larger part of Professor Hull's 
 book, however, is devoted to the consideration of the 
 Palaeozoic periods and the origin of the Atlantic" Ocean ; 
 the space allotted to the Neozoic periods being hardly 
 proportionate to the knowledge that we really possess 
 concerning them. 
 
 The aim and scope of the present volume are somewhat 
 different from Professor Hull's, the successive periods of 
 Neozoic time being treated at much greater length than 
 those of Palaeozoic time, partly because much more infor- 
 mation is available, but chiefly because it is my object to 
 trace out the succession of physical and geographical 
 changes which have led up to the existing disposition 
 of land and water in the north-western portion of 
 Europe. 
 
 My thanks are due to many friends and correspondents 
 for information and advice, especially to Dr. Callaway 
 with regard to the Cambrian period, to Professor Hull 
 respecting the Irish Devonians, to Professor A. H. Green, 
 Mr. E. Wilson, and Mr. H. B. Woodward in connection 
 with the Carboniferous, Permian, and Jurassic periods 
 
PREFACE. VLL 
 
 respectively, and lastly to Mr. Whitaker for his kindness 
 in reading the proofs of the Tertiary chapters, and for 
 many suggestions thereon. 
 
 A. J. JT7KES-BBOWNE. 
 
 May, 1888. 
 
 N.B. The reader is requested to make the alterations 
 indicated in the list of errata. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTION 1 
 
 Shallow-water beds ; Deep-water beds ; Variations in 
 thickness ; Unconformities ; Difficulties of Geographical Re- 
 storation. 
 
 CHAPTER I. ARCHXAN TIME . ..."... 13 
 CHAPTER II. CAMBRIAN PERIOD 16 
 
 1. Stratigraphical Evidence. 2. Geographical Restora- 
 tion. 
 
 CHAPTER III. ORDOVICIAN PERIOD 27 
 
 1. Stratigraphical Evidence ; England, Scotland, Ireland. 
 2. Geographical Restoration. 
 
 CHAPTER IV. SILURIAN PERIOD 40 
 
 1. Stratigraphical Evidence. 2. Geographical Resto- 
 ration. 
 
 CHAPTER V. OLD RED SANDSTONE AND DEVONIAN . . 49 
 
 1. Stratigraphical Evidence; Classification, Lower Old 
 Red Series, Devonian System, Upper Old Red Sandstone. 
 2. Geographical Restoration. 
 
 CHAPTER VI. CARBONIFEROUS PERIOD 69 
 
 1. Stratigraphical Evidence; Classification, Coast-lines. 
 2. Geographical Restoration. 3. Physical changes during 
 the period. 
 
 CHAPTER VII. DTASSIC OR PERMIAN PERIOD . . .102 
 
 1. Stratigraphical Evidence. 2. Geographical Resto- 
 ration. 
 
X CONTENTS. 
 
 PAGE 
 
 CHAPTER VIII. TRIASSIC PERIOD 114 
 
 1. Stratigraphical Evidence ; Bunter, Keuper. 2. Geo- 
 graphical Restoration, land surfaces, the great salt-lake. 
 
 CHAPTER IX. JURASSIC PERIOD 134 
 
 1. Stratigraphical Evidence; Rhsetic and Lias, Middle 
 Jurassic series, Upper Jurassic series. 2. Physical His- 
 tory and Geography ; Lower Jurassic time, Middle Jurassic 
 time, Upper Jurassic time. 
 
 CHAPTER X. CRETACEOUS PERIOD ..... 163 
 
 1. Stratigraphical Evidence; Lower Cretaceous, Upper 
 Cretaceous. 2. Geographical Restoration ; the Wealden 
 Lake, the Vectian Sea, Upper Cretaceous subsidence. 
 
 CHAPTER XI. HANTONIAN PERIOD 196 
 
 1. Stratigraphical Evidence ; Eocene, Oligocene. 2. Geo- 
 graphical Restoration ; Eocene time, Oligocene time, general 
 upheaval of Europe. 
 
 CHAPTER XII. ICENIAN PERIOD 235 
 
 1. Stratigraphical Evidence; Miocene, Pliocene. 2. 
 Geographical Restoration ; Miocene time, Older Pliocene 
 time, Newer Pliocene time. 
 
 CHAPTER XIII. ICENIAN PERIOD, PLEISTOCENE . . . 261 
 
 1. Stratigraphical Evidence; Scotland, England and 
 Wales, Ireland. 2. Physical History and Geographical 
 Changes ; Formation of Boulder-clay, Continental conditions, 
 Subsidence and isolation of the British Islands. 
 
 CHAPTER XIV. SUMMARY or THE GEOGRAPHICAL EVOLUTION 
 
 OF THE BRITISH ISLANDS 304 
 
 Uncertainty of pre-Carboniferous geographies ; post-Car- 
 boniferous changes ; the Triassic continent ; the successive 
 changes which resulted in the formation of the Pliocene landj 
 the isolation of Britain. 
 
 CHAPTER XV. THE THEORY OF THE PERMANENCE OF OCEANS 
 
 AND CONTINENTS 324 
 
 Professor Dana's hypothesis; Dr. Wallace's arguments 
 considered ; conclusions and a different theory suggested. 
 
 INDEX . . . 337 
 
LIST OF PLATES. 
 
 N.B. In each map the horizontal blue lines represent the area which 
 is supposed to have been covered by the sea. 
 
 PAGE 
 
 PLATE I. Hypothetical Restoration of early Ordovician geo- 
 graphy (Arenig epoch) 36 
 
 PLATE II. Hypothetical Restoration of Silurian geography (Llan- 
 
 dovery or Valentian epoch) 46 
 
 PLATE III. Supposed geography of Lower Devonian and Old 
 
 Red Sandstone time 60 
 
 PLATE IV. A Restoration of Lower Carboniferous geography 
 
 (Lower Shale and Limestone epoch) .... 86 
 
 PLATE V. Geography of the Permian or Dyassic period . . 106 
 
 PLATE VI. Geography of the Triassic period (Keuper) . . 130 
 
 PLATE VII. Geography of the Lias and Inferior Oolite . .150 
 
 PLATE VIII. Geography of the Portlandiau epoch . . .160 
 
 PLATE IX. Geography of the later part of the Vectian period 
 
 (Aptien) 186 
 
 PLATE X. Geography of the Upper Greensand epoch . . 190 
 
 PLATE XI. Geography of the Lower Eocene (Thanet Beds and 
 
 London Clay) . 222 
 
 PLATE XII. Geography of Oligocene time .... 232 
 
 PLATE XIII. Geography of later Pliocene time (the closer lines 
 representing the extent of the sea at the time of the Forest 
 Bed) 258 
 
 PLATE XIV. Pleistocene geography, coast-line coinciding with 
 
 contour of 80 fathoms 294 
 
 PLATE XV. Pleistocene geography, coast-line coinciding with 
 
 contour of 40 fattcms ..... 300 
 
EEEATA. 
 
 Page 118, line 24, for Dallaston, read Darlaston. 
 Page 162, line 21, for geologial, read geological. 
 Page 187, line 5, for Plate VIII. , read Plate IX. 
 Page 190, line 8, for Plate IX., read Plate X. 
 
iv 
 
 INTRODUCTION. 
 
 r I "'HE existing geographical and physical contours of 
 J_ the British Islands are the outcome of the long and 
 varied geological history which this particular part of the 
 world possesses. There are few other regions of the earth's 
 surface which in so small an area exhibit so many dif- 
 ferent systems of rocks as are to be found in the British 
 Islands. England alone includes portions of nearly all 
 the rock-systems which are found on the continent of 
 Europe. 
 
 Each of these rock-groups was formed during the main- 
 tenance of certain physical and geographical conditions, and 
 the restoration of the particular conditions which prevailed 
 during any one period will reveal one phase in the geo- 
 graphical evolution of Britain. Further, in the multi- 
 plicity of rock-groups we have proof that changes in the 
 physical conditions of the area have been frequent, and it 
 becomes evident that the history of this evolution is a 
 long one ; it is, in fact, a history of alternate upheaval 
 and depression, of the repeated formation of islands and 
 continents, and of their subsequent detrition and submer- 
 gence. In this long succession of changes there have been 
 many different arrangements of land and sea over the 
 area where the British Isles now stand ; every part of our 
 country has been repeatedly depressed beneath the sea, 
 though some parts have been submerged much more fre- 
 
2 INTRODUCTION. 
 
 quently than others, and conversely every part of the area 
 which is now covered by the environing seas has more than 
 once been part of the dry land. Sometimes nearly the 
 whole area has formed part of continental land, and at 
 other times it has been almost entirely submerged beneath 
 the sea. 
 
 But we can look back to an epoch in the geographical 
 history of Britain when the foundations of our islands had 
 been laid, and when the older and more mountainous parts 
 of the country had been brought into the relative positions 
 which they now occupy. We may, in fact, regard the 
 Palaeozoic districts of the British Islands as portions of 
 ancient lands which have been broken up and reduced to 
 their present dimensions during successive periods of 
 erosion and denudation ; these tracts and the vanished 
 lands of which they formed part have yielded the ma- 
 terials that compose the more recent (Neozoic) strata, 
 and there were at least three periods in these later times 
 when Neozoic strata filled up the gaps between the older 
 blocks of ground and welded the British Islands into a 
 continental whole. Erosion and submergence, however, 
 again began the work of destruction and separation, with 
 the ultimate result of reducing them once more to the state 
 of islands and of giving them the outlines which they 
 now present. 
 
 Before proceeding to describe the successive phases of 
 this process of geographical evolution, some consideration 
 of the evidence on which we have to rely in trying to 
 restore the geography of any period seems to be desirable. 
 The greater part of the strata with which the geologist has 
 to deal are marine deposits, and it is only rarely that actual 
 proof of the former existence of land in any district is 
 found in the intercalation of purely freshwater deposits. 
 Occasionally we meet with estuarine beds which indicate 
 the close proximity of land ; and of more frequent occur- 
 
INTRODUCTION. 3 
 
 rence are conglomerates and breccias recalling those which 
 are formed along modern beaches. But in many cases the 
 position of the land tracts during a given period can only 
 be inferred from general considerations, such as the 
 changes in the lithological characters of the sediments, the 
 thinning or thickening of beds in certain directions, their 
 entire absence in certain areas, their conformity or uncon- 
 formity to the underlying rocks. 
 
 Shallow-water Beds. In the first place, therefore, we 
 must know what kinds of rock are likely to have been 
 formed in shallow water. As a general rule, the coarser 
 the grain of the rock the shallower was the water in which 
 it was formed, and the nearer was the shore from whence 
 the component materials were derived, or along which they 
 were moved. Conglomerates consisting of stones which 
 could only be moved by the beating of waves on a shore 
 are, of course, decided evidence of the close neighbourhood 
 of land to the spot where we now find them, and if they 
 contain large angular or sub-angular boulders we may 
 infer that they have been formed below a line of cliffs, and 
 further, if such deposits form a mass of considerable thick- 
 ness, it is probable that much of the material was brought 
 down by floods and torrents from a range of hills above 
 the coast-line. 
 
 We must remember, however, that such coarse deposits 
 are not formed everywhere along a line of coast, and that 
 sandstones may have been formed as close to a shore as 
 conglomerates ; nay, some sandstones have, doubtless, been 
 formed above high water, and were originally sand-dunes, 
 such as are common on our present coasts. 
 
 Sandstones formed from seolian drift, or blown sand, 
 may generally be distinguished from water-borne sands by 
 the character of their component quartz grains ; those of the 
 former being all much worn, rounded, and polished, while 
 in the latter a large proportion of the grains are angular. 
 
4 INTRODUCTION. 
 
 Professor Daubree l and the late Mr. J. A. Phillips 2 have 
 shown that the wearing down and rounding of angular 
 quartz grains is an exceedingly slow operation, and that 
 grain of quartz one-fiftieth of an inch in diameter requires 
 an amount of abrasion equal to that which would result from 
 its having travelled a distance of 3,000 miles in water be- 
 fore it becomes so rounded as to assume the form of a 
 miniature pebble. In sand from the seashore of Cornwall 
 Mr. Phillips found that the quartz grains between one- 
 twentieth and one-fiftieth of an inch diameter were still 
 angular, although they had been for years exposed to the 
 beating of the waves. Only a few of the larger grains 
 were partially rounded, and the same is the case with the 
 sands of other shores. 
 
 The sands of the African and Arabian deserts, on the 
 contrary, consist of completely rounded grains without 
 any admixture of angular fragments, and the grains of 
 blown sand from English dunes only differ in being rather 
 less completely rounded. Most sandstones consist of more 
 or less angular grains, but beds of consolidated seolian sand 
 exist in some formations. 
 
 Pure quartzose sandstones of marine origin are always 
 shallow-water deposits and are seldom found in deeper 
 water than fifty or sixty fathoms, except where the bottom 
 slopes very steeply from the coast ; neither do they gene- 
 rally occur at a greater distance than twenty or thirty 
 miles from land, except in shallow and land- surrounded 
 seas like that which is sometimes called the German Ocean. 
 
 Outside a continent which has a fairly uniform coast-line 
 trending for a long distance in one direction there is gene- 
 rally a regular succession of deposits from the coast-margin 
 outwards, the coarseness of the materials decreasing with 
 the distance from land, so that we pass from shingle or 
 
 1 " Geologie ExpSrimentale," p. 256 et seq. 
 
 2 " Quart. Journ. Geol. Soc.," vol. xxxvii. p. 21. 
 
INTRODUCTION. O 
 
 coarse sand to fine sand, silt, clay, and calcareous mud. 
 But along coasts which have many inlets or bays this 
 order is not so well preserved, and fine silts or muds are 
 sometimes formed quite close in shore ; similar deposits of 
 very fine grain occur also in the estuaries of large rivers. 
 
 In dealing, therefore, with clays and shales we must be 
 guided largely by their fossil contents, and by the nature 
 of the other beds with which they are associated, in de- 
 ciding whether they are shallow or deep-water deposits. 
 Black carbonaceous clays, for instance, containing much 
 organic matter and associated with sandstones, would lead 
 us to suspect the neighbourhood of a swampy shore or the 
 estuary of a large river. 
 
 Limestones, again, though more often formed in com- 
 paratively deep water at a distance from land, are some- 
 times accumulated quite close to a coast-line, like the 
 coral limestones of the present day. A pure limestone 
 may be taken as a proof of clear water, and if there is 
 reason to suppose that it was formed at no great distance 
 from land, it may be assumed that no large rivers issued 
 from the coast in question. 
 
 Every case in which limestones occur must be dealt with 
 on its own merits, and no hasty conclusion as to the dis- 
 tance of land should be formed. There is, in fact, no 
 rock-name that includes so many varieties as limestone, 
 and the conditions under which a limestone may be formed 
 are as numerous as are the varieties. That many of the 
 limestones which occur among British rocks are shallow- 
 water deposits is generally admitted ; no one would claim 
 a deep-water origin for a current-bedded oolitic limestone, 
 or for the Llandovery limestones, which succeed sandstones 
 and conglomerates, or for the Liassic limestones of Gla- 
 morganshire. The Carboniferous limestones of Northum- 
 berland and Scotland can hardly have been deep-water beds, 
 and perhaps none of the Carboniferous limestone, even in 
 
O INTRODUCTION. 
 
 its more massive facies, was formed very far from land, 
 though the water was doubtless clear and deep in those 
 places where it attains great thickness. 
 
 Deep-water Beds. It is now generally acknowledged 
 that the great mass of the rocks which compose our 
 modern continents are such as are now only formed within 
 200 or 300 miles of land, and very seldom include any 
 deposits which resemble those now accumulating in the 
 depths of the Atlantic and Pacific Oceans. There is only 
 one formation in Britain which was undoubtedly accumu- 
 lated in deep water at a great distance from land of a 
 continental character, and that is the Chalk. When, there- 
 fore, we speak of deep-water beds, it must be remembered 
 that comparatively deep water is meant, and not water of 
 oceanic depth. 
 
 Massive compact limestones and calcareous clays or 
 marls have generally been formed in water of considerable 
 depth. Many bluish and greenish clays, shales and slates, 
 especially such as do not contain many fossils, have doubt- 
 less been formed in deep water, and are comparable to the 
 blue and green muds which are found over certain tracts 
 of the sea bottom, between the shallow water and the 
 deeper tracts of the ocean. 
 
 Variations in Thickness. The evidence derivable from 
 the thinning and thickening of deposits also merits some 
 examination. If we consider the case of sediment which is 
 being transported by the action of a current setting off a 
 coast-line, there can be little doubt that the greatest 
 amount of sediment would be thrown down at a certain 
 distance from land, where the bottom began to shelve 
 into deep water. Little could be deposited in the shallow 
 water near shore, but would be carried to a greater or less 
 distance in proportion to the depth of the water ; and if 
 the bottom shelved gradually the deposit might cover a 
 considerable space, .but as soon as fairly deep water was 
 
INTRODUCTION. . 7 
 
 reached most of the sediment would subside, and little 
 would be left to travel farther. A deposit formed under 
 these conditions would form a large lenticular mass which 
 would thin out principally in two directions, viz., in the 
 direction of open sea and in the direction of land. Subsi- 
 dence would make no difference to this arrangement, but 
 would only tend to increase the thickness of the deposit. 
 
 The deposit would also thin out laterally, away from the 
 central axis of deposition, but a transverse section across 
 the mass would exhibit a different appearance from a 
 longitudinal section ; in a longitudinal section the size and 
 nature of the particles composing the deposit would be 
 nearly the same throughout, while in a transverse section 
 we should find a gradation from coarse sand to fine 
 mud. 
 
 When, therefore, we are dealing with a deposit, or a 
 group of beds, which is thinning out in a certain direction, 
 no conclusion should be drawn without having regard to 
 their lithological characters, and whether these change in 
 that direction or not. Thus, if we start with a thick mass 
 of shale or clay, the materials of which must have been 
 derived from the land, and we find that this simply be- 
 comes thinner without change of character or replacement 
 by other deposits, we can only infer that we are passing 
 away from the source of supply, possibly toward what was 
 deep water, but more probably in a lateral direction from 
 the major axis of deposition. If, however, as it diminishes 
 in thickness, it becomes decidedly more calcareous, assum- 
 ing the character of a marl and including beds of limestone, 
 we may assume that we are proceeding away from the con- 
 temporaneous land and toward what was then an area of 
 clear and deep water. If, on the other hand, a thick argil- 
 laceous deposit is gradually replaced by beds of sandstone, 
 and these by pebbly and conglomeratic beds, there can be 
 no doubt that the position of the contemporaneous land 
 
8 INTRODUCTION. 
 
 is indicated by the direction in which the coarser beds 
 set in. 
 
 We may note here that the formation is likely to be 
 thickest along the tract where shales and sandstones 
 alternate with each other, and as sandstones are more 
 rapidly accumulated than clays, the formation may thicken 
 landwards by the intercalation of sandstones ; so that if 
 only this portion of a group of beds is preserved to us, the 
 direction of the land will be indicated by the thickening 
 of the sandstones and the thinning of the shales. Among 
 the Palaeozoic rocks this is sometimes the only kind of 
 evidence we possess to guide us toward the position of the 
 land areas. 
 
 The Evidence of Unconformities. The existence of a 
 widespread unconformity in any district, accompanied by 
 the absence of certain groups of rocks which occur in 
 neighbouring districts, raises the presumption that the 
 first district was a land tract during the period which these 
 rocks represent. Unconformities are therefore very im- 
 portant guides in the restoration of ancient geographies, 
 because we may regard the eroded surface as the actual 
 relic of an ancient land. It does not, of course, present 
 all the physical features of that ancient land, because the 
 surface has always been greatly modified as its successive 
 levels came within the erosive powers of the sea under 
 which it sank. Still we can often tell whether it was ori- 
 ginally a high and hilly land, or whether it was of no great 
 elevation. 
 
 In drawing inferences, however, from the absence of 
 certain formations above a surface of unconformity, some 
 caution must be exercised. If an unconformity occurs 
 between two systems which are in geological sequence, 
 such as the Ordovician and the Silurian, or between two 
 parts of the same system, we must conclude that the older 
 set of rocks was elevated during the epoch which is repre- 
 
INTRODUCTION. 9 
 
 sented by the missing groups. And again, if a whole 
 system of rocks be absent, we may reasonably suppose 
 that the area in question was land throughout the whole 
 of that particular period. 
 
 If, however, the gap is very great, and several systems 
 of rocks are missing, we must not conclude that the area 
 has been continually above water during the whole of the 
 periods of time which are unrepresented. The area may 
 have been submerged more than once in the interval, and 
 may have received deposits belonging to more than one of 
 the absent systems, but all remnants of these deposits 
 may have been swept away during the erosion which 
 accompanied and followed the last elevation. Thus the 
 Trias rests in many places on Silurian or Devonian rocks, 
 but it is probable that in most of these cases the older 
 rocks had sunk beneath the Carboniferous sea, and had 
 originally been covered with some portion at least of the 
 Carboniferous system; the Dyassic or Permian period, 
 which preceded the Carboniferous, was one of great dis- 
 turbance and denudation, and large areas of Carboniferous 
 strata were then broken up and removed, so that the 
 absence of these strata at the localities in question was 
 probably due to this erosion. Such an unconformity may 
 then be evidence of land in Dyassic times, but affords no 
 clue to the position of the land tracts in the Carboniferous 
 period. 
 
 In cases of unconformity the rocks which rest directly 
 upon the old land surface are generally conglomerates 
 or pebbly sandstones, the materials of which have been 
 derived from the rocks of which that land was composed. 
 Such conglomerates often cover very large surfaces, but it 
 is well to remember that such beds are not the invariable 
 accompaniments of unconformity. Thus, where a tract of 
 land has sunk slowly beneath the sea for a long period of 
 time, so that the newer deposits have overlapped one 
 
10 INTRODUCTION. 
 
 another against its sloping surface, the lower portion of 
 the newer series may be margined by conglomerates, while 
 the higher portion is not ; the latter may consist of shales 
 and sandstones, with perhaps barely a foot of pebbly mate- 
 rial at their base. Instances of such overlap with an 
 absence of conglomerates are common in the case of the 
 Carboniferous system ; where the Lower Carboniferous rocks 
 lie unconf ormably on older strata, conglomerates and pebbly 
 sandstones are always present, but where the Coal-Mea- 
 sures overlap the lower group and lie on older beds, they 
 often rest directly on the surface of the latter without the 
 intervention of any conglomerate, and with only a thin 
 pebbly basement bed. So also in the east of England, 
 where an ancient land surface is buried beneath the Creta- 
 ceous rocks, the G-ault clay overlaps the sandstones and 
 rests on the older rocks with a mere basement bed, which 
 is generally only a foot in thickness. 
 
 When such cases occur we may perhaps infer that the 
 extent and height of the land had been so reduced by con- 
 tinued submergence that the area remaining was small 
 and of low elevation above the sea, so that the conditions 
 were unfavourable for the formation of conglomeratic beds. 
 In many cases the tract of land had doubtless been re- 
 duced to the condition of an island, an isthmus, or a low 
 promontory. 
 
 The Difficulties of Geographical Restoration. These arise 
 chiefly from two causes the imperfection of our know- 
 ledge and the imperfection of the geological record. The 
 first is being gradually removed by the industry of geolo- 
 gists, but there are still many parts of the British Islands 
 about the geological structure of which we really know 
 very little, and there are many others about which more 
 detailed information is much to be desired. Again, there 
 are very large areas where the older rocks exist, but where 
 they are buried and concealed from view by the newer for- 
 
INTRODUCTION. 11 
 
 nations ; thus we hardly know anything of the subterranean 
 geology of the large areas which are covered by strata of 
 Carboniferous age both in England and Ireland. Other 
 areas again are concealed by the Neozoic strata, and we 
 are only just beginning to obtain some knowledge of the 
 underground limits of the older Neozoic rocks, by means 
 of the deep borings which have been made from time to 
 time in the eastern part of England. 
 
 The imperfection of the geological record is another 
 great source of difficulty, and one which will never be alto- 
 gether overcome. The rocks which remain to us as the 
 records of any one period are but a remnant of the depo- 
 sits which were formed during that period, and yet before 
 we can attempt to restore the geography of that time we 
 must replace in imagination the rocks which are lost, so 
 as to form a conception of the space over which they origi- 
 nally extended. For some portions of the space this may 
 be easily done, as in the case of conformable beds lying on 
 each side of an anticlinal, but when the final limit of 
 a formation toward a given direction is a fault or an 
 abrupt boundary, without even an outlier beyond, we are 
 left in complete uncertainty as to the original limits of 
 those beds in that direction. Under such circumstances 
 we are obliged to fall back on general considerations, such 
 as the lithological changes seen in the exposed areas and 
 the physical characters of the country beyond the present 
 boundary of the formation ; still it must be admitted that 
 in many such cases any attempt at geographical resto- 
 ration partakes more or less of the nature of guess-work. 
 
 I must, therefore, ask my readers to remember that 
 some of the restorations attempted in the following chapters, 
 especially those of the earlier periods of geological history, 
 are built on slight foundations, and may have to be modi- 
 fied by the results of new discoveries. In some instances 
 the facts which are known suggest different inferences to 
 
12 INTRODUCTION. 
 
 different minds, and there are several cases in which diffe- 
 rent views are held with regard to a certain area having 
 been above or below water during a certain period. In 
 such cases I have carefully examined the different views 
 which have been taken by those who have written on the 
 subject, before selecting that which appeared to be the 
 most probable interpretation of the facts. 
 
CHAPTEE I. 
 
 TIME. 
 
 BELOW the oldest rocks which contain definite organic 
 remains there are in certain parts of the British 
 Islands still older rocks, which are now generally known 
 by the name of Archaean, as being the most ancient rock- 
 masses that have yet been recognized in the earth's crust. 
 They are also called Pre-Cambrian, for their infra-position 
 to the Cambrian rocks is the real proof of their antiquity. 
 
 In England, the principal Archaean tracts occur in South 
 Wales (Pembrokeshire), North Wales (Carnarvon and 
 Anglesey), Shropshire (Wrekin and Caradoc range), Charn- 
 wood Forest, the Malvern Hills, and the Lizard peninsula. 
 In Scotland, the Hebrides, as well as parts of Eoss and 
 Sutherland, consist of Archaean rocks. In Ireland, they 
 occur in Donegal and G-alway. 
 
 The Archaean rocks are all more or less metamorphic ; 
 some are distinctly crystalline and foliated, others are as 
 clearly volcanic ashes and lavas, while some seem to be of 
 sedimentary origin, such as the quartzites and limestones. 
 The general opinion is that these Pre-Cambrian rocks are 
 divisible into two great groups, 1 which may or may not 
 belong to distinct systems. The older group consists 
 chiefly of gneiss, which is often so granitoid as to resemble 
 a true granite ; the newer group is composed either of vol- 
 
 1 Callaway, " Geol. Mag.," Dec. 3, vol. ii. p. 258. 
 
14 ARCHJSAN TIME. [CHAP. I. 
 
 canic rocks, felspathic lavas and ashes, or of hypocrystalline 
 rocks, including schists of many kinds, quartzites, dolo- 
 mites, and altered grits. 
 
 Some geologists think that the upper group lies un- 
 conformably on the lower, and that they should be regarded 
 as widely separated systems ; others think that the appa- 
 rent unconformity is only a local one connected with the 
 volcanic origin of the newer group ; while some and 
 particularly Dr. A. G-eikie regard the granitoidite as 
 truly igneous rock of later date than the hypocrystalline 
 strata. 
 
 It is obvious that while such diverse opinions exist with 
 regard to the relations of the Archaean rocks, little can be 
 said concerning their probable origin and mode of forma- 
 tion, or concerning the physical conditions of the earth's 
 surface at this early period of its history. Mr. J. E. Marr 
 has even ventured to doubt whether any of the Archaean 
 rocks were originally marine sediments ; he points to the 
 great amount of volcanic activity which is testified by the 
 intrusive and eruptive rocks of the Welsh, Shropshire, and 
 Charnwood districts, and he suggests that even some of 
 the hornblendic and chloritic schistose rocks may only be 
 metamorphosed tuft's. The limestones are thin, lenticular 
 beds, and might, he thinks, have been formed in lakes, or 
 by the calcareous springs which are common in volcanic 
 districts. 
 
 From these and other facts he concludes that Archaean 
 time was one of continued and universal vulcanicity, and 
 that the amount of erosion and denudation which took 
 place at its close was so violent, rapid, and extensive that 
 great masses of rock, which had been metamorphosed at a 
 considerable depth below the original Archaean land, were 
 in many places brought to the surface ; while the greater 
 part of the unaltered surface rocks were swept away and 
 re- deposited as Cambrian sediment. 
 
CHAP. I.] ABCH^AN TIME. 15 
 
 Dr. Callaway's inquiries into the genesis of the gneissic 
 rocks of the Malvern Hills, and Mr. Peach's experience of 
 the Archaean rocks of Scotland, though not exactly corro- 
 borating Mr. Marr's views, are certainly not at variance 
 with them. Dr. Callaway believes that the hornblende- 
 gneiss of Malvern is a crushed and modified diorite ; 
 that the mica- schists have been similarly formed from 
 f elsite, and the mica-gneiss from granite ; l while he 
 considers some of the banded gneisses were produced by 
 earth-pressures acting upon complex interveining of granite 
 in diorite, resulting in a parallelism of the veins ; so that 
 he would regard many of the Archaean gneisses and schists 
 as metamorphosed igneous rocks, and not as metamorphosed 
 sedimentary rocks. Mr. Peach says : 2 " The gneisses all 
 bear evidence of having been formed by the crushing and re- 
 crystallization of igneous rocks, their schistosity being due 
 to mechanical movement of the particles produced by 
 differential pressure." 
 
 Without entirely acquiescing in Mr. Marr's hypothesis, 
 there can be little doubt that a large portion of the British 
 Archaean rocks are of igneous origin, and that only a small 
 proportion are sedimentary, and that they were accumu- 
 lated in a volcanic district which was eventually elevated 
 into lofty mountain ranges. 
 
 1 " Quart. Journ. Geol. Soc.," vol. xliii. p. 525. 
 
 2 " Proc. Roy. Phys. Soc.," vol. ix. p. 23. 
 
CHAPTEE II. 
 
 CAMBRIAN PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 rocks rise to the surface in several parts 
 of the British Islands, but they nowhere occupy any 
 very large tract of country, so that we can only compare 
 their isolated exposures, and cannot trace their strati- 
 graphical variations from one district to another. In 
 England and Wales there are five districts where rocks 
 referable to the Cambrian system occur South Wales, 
 North Wales, Shropshire, Warwickshire, and the Malvern 
 Hills. 
 
 Wherever the base of the system is exposed, the base- 
 ment bed is found to be a conglomerate containing frag- 
 ments of Archaean rocks, and resting unconformably on a 
 very uneven surface of those rocks ; the conglomerate being 
 probably in process of formation at different levels through- 
 out the whole of the period, and belonging, therefore, to 
 different stages at different places. 
 
 The Lower Cambrian rocks are not known to exist east 
 of the Longmynd, but Upper Cambrian shales have been 
 found in Warwickshire, and may occur at intervals beneath 
 many parts of our Midland and Eastern counties. 
 
 The stratigraphy of the Cambrian rocks is not yet com- 
 pletely understood; there are many unsolved difficulties 
 connected with them, and any account of them must at 
 present be regarded as provisional. 
 
CHAP. II.] CAMBRIAN PERIOD. 17 
 
 In Wales the normal succession of the Cambrian rocks 
 is as follows : 
 
 Tremadoc slates, 1,000 to 2,000 feet . . . . \ ^ 
 Lingula Flags, a group of sandy flagstones and slates, I 
 
 2,000 to 5,000 feet /Cambrian. 
 
 Meuevian slates, 200 to 750 feet \ 
 
 Harlech Beds, red, green, and purple grits and slates, i- ^ e * 
 
 3,000 to 9,000 feet /Cambrian. 
 
 The Harlech Beds of Merioneth are more than 8,000 
 feet thick, and the base is not there seen, but when they 
 reappear on the west side of the Snowdon range, they are 
 much thinner, and are probably not more than 3,000 feet 
 thick, including the basal conglomerate of Llyn Padarn, 
 which lies on the eastern flank of the main Archaean ridge. 
 On the west side of this ridge the basal conglomerate is 
 overlain by grits and slates, and, near Bangor, by sand- 
 stones and mudstones, which have been referred to the 
 Harlech series, but it is quite possible that they are shore 
 beds of Lingula Flag age. As they are directly succeeded 
 by Arenig slates (Ordovician), it does not seem probable 
 that the Lingula Flags should be entirely absent, for the 
 lowest beds usually thin out before the higher. If, there- 
 fore, we regard the greater part of the Bangor Cambrians 
 as Lingula Flags, it follows that in the space of about two 
 miles the Harlech series has thinned from 3,000 feet to, 
 perhaps, 100 feet of grit and conglomerate. This suggests 
 that the surface of the Archaean rock formed a steep slope, 
 inclining to the south-east, when the Cambrians were 
 deposited against it. 
 
 In Shropshire the same thing seems to take place on a 
 still larger and more surprising scale ; for the rocks of 
 the Longmynd, which are supposed to be of Lower Cambrian 
 age, and which lithologically resemble the Llanberis grits 
 and slates, have a great thickness (possibly 10,000 feet), 
 and are faulted on each side against tracts of undoubted 
 
 c 
 
18 PALEOZOIC TIME. [CHAP. II. 
 
 Archaean rock. But the eastern or Caradoc Archaean ridge 
 is flanked on the other side by a quartzite conglomerate, 
 which is succeeded by sandstones of Middle or Upper 
 Lingula Flag age ; the Lower Cambrian being entirely 
 absent. How can this sudden disappearance of so thick 
 a mass of rock be accounted for ? There seem to be only 
 three possible ways of meeting the difficulty : 
 
 (1) That the Longmyndian sediments were raised into 
 a block of land about the epoch of the Menevian Beds, and 
 that this block afterwards sank again to receive the upper 
 half of the Lingula Flags and the Tremadoc Slates. 
 
 (2) That the Caer Caradoc range was the border of a 
 mass of Archaean land, and formed a precipice or steep de- 
 clivity about 10,000 feet high, so that it was not over-topped 
 by the Cambrian Sea till the time of the Lingula Flags. 
 
 (3) That the faults on the east side of the Longmynd 
 and Caradoc ranges are thrust planes, bringing together 
 portions of districts which were originally many miles 
 apart. But the faults appear to be of the normal kind, 
 and there is no evidence of the great crushing which must 
 accompany lateral thrust. 
 
 If none of these suggestions are considered satisfactory, 
 it can only be argued that the Cambrian age of the Long- 
 mynd rocks is an assumption, and that the facts of the 
 case show them to be physically more closely connected 
 with the Archaean than with the Upper Cambrian. It is 
 indeed quite possible that they are pre-Cambrian, and 
 belong to the interval which is elsewhere represented by 
 the gap between the Archaean and the Cambrian. 
 
 If, however, they should prove to be of Lower Cambrian 
 age, we must select the first of the above hypotheses as the 
 least unlikely, and must suppose that an upheaval took 
 place in the middle of the Cambrian period, but that the 
 land so formed was soon submerged again beneath the 
 sea of the Lingula Flags. 
 
CHAP. II.] CAMBRIAN PERIOD. 19 
 
 In South Wales there are indications of a similarly rapid 
 disappearance of Lower Cambrian sediments. Near St. 
 Davids these beds are only 4,000 feet thick, which is 
 about half their thickness in Merioneth. Whether they 
 thin eastward in the trough between the two principal 
 Archaean tracts is not yet known, but at Trefgarn on the 
 south-east side of the eastern massif no Harlech Beds or 
 Menevian are found, and the Upper Lingula Flags with 
 a basal conglomerate appear to rest on the Archaean. It is 
 true there are some signs of faulting, and Dr. Hicks believes 
 the Lower beds are faulted out, but more evidence of this 
 is required. 
 
 Dr. Callaway favours me with the following remarks on 
 the lithological composition of the Lower Cambrian rocks :, 
 "These sediments show that the adjoining lands were 
 partly built up of granitic, volcanic, and metamorphic 
 rocks. The purple conglomerates and sandstones of the 
 Longmyndian, reaching a thickness of several thousand 
 feet, as well as the broad band of pale-green slates which 
 skirts the eastern side of the Longmynd, are largely derived 
 from the rhyolites of the Uriconian and indicate the 
 proximity of an extensive land area. Bounded fragments 
 of granitic and schistose rocks are not uncommon in the 
 conglomerates, while the grains of quartz and felspar in 
 the grits have probably the same origin. These grits grow 
 less felsitic towards the south, and fragments of metamor- 
 phic rocks increase in number indications which suggest 
 the conclusion that the Malvern Hills are a worn fragment 
 of a mass of land which made a conspicuous feature in the 
 Longmyndian ocean. 
 
 " The rocks of North and South Wales afford similar 
 evidence. The conglomerates of Moel Tryfaen and the 
 sandstones further west contain a very large proportion of 
 fragments of f el site similar to the Archaean rhyolite near 
 Carnarvon, while the massive grits of the Merionethshire 
 
20 PALEOZOIC TIME. [CHAP. II. 
 
 anticline, though very quartzose, are partially constructed 
 of felsite grains." 
 
 If we next consider the Upper Cambrian we find they 
 also are thickest in Merioneth, being there no less than 
 7,000 feet thick. Near Llanberis, west of Snowdon, the 
 Lingula Flags are only 2,300 feet, and there is little that 
 can be called Tremadoc. Finally, near Bangor, the Lingula 
 Flags are represented by sandstones and muds tones resting 
 on the grits which overlie the basal conglomerate ; even if 
 the basement beds are also part of the same series (see 
 ante, p. 17) the total thickness is not more than 1,000 feet, 
 and there is no representative of the Tremadoc. 
 
 A similar change takes place southward ; near St. Davids 
 the Lingula Flags are not more than 2,000 feet thick, and 
 consist largely of sandstones and flags, many of the beds 
 showing ripple marks, and all attesting shore conditions. 
 The Tremadoc slates are 1,000 feet thick. 
 
 At Malvern there is 500 feet of sandstone resting on 
 Archaean, and overlain by 1,000 feet of shale belonging to 
 the Dolgelly and Tremadoc groups, and in Shropshire there 
 is a similar sequence. In Warwickshire, however, the series 
 again thickens ; there is a massive quartzite of uncertain 
 age, but probably Upper Cambrian, overlain by 2,000 feet 
 of Upper Cambrian shale. 
 
 The Cambrian rocks of Wales seem, therefore, to have 
 been formed in a deep trough between lofty ridges formed 
 of the Archaean rocks on the east and on the west, and 
 possibly also to the south-east. 
 
 The only Irish rocks referable to the Cambrian system are 
 those in Wicklow and Wexf ord. 1 Lithologically they are com- 
 parable to the Lower Cambrian of Wales and Shropshire, 
 but as their base is not seen, we do not know on what they 
 rest, and no definite fossils have yet been found in them. 
 
 1 The Galway rocks, regarded as Cambrian by Mr. Kinahan, are 
 more probably of Archaean age. 
 
CHAP. II.] CAMBRIAN PERIOD. 21 
 
 In Scotland we once more find rocks resting on un- . 
 doubted Archaean and covered by Ordovician, but they 
 are very different lithologically from the Cambrian of 
 Wales. They consist entirely of red felspathic sandstones, 
 with beds of breccia and conglomerate at the base, and 
 are in places from 3,000 to 4,000 feet thick. This Torridon 
 Sandstone is probably of early Cambrian age, and has 
 evidently been formed against an Archaean coast-line. Its 
 composition is thus described by Professor Bonney l : "Its 
 coarser basement beds are crowded with fragments of the 
 underlying gneisses and schists, and since the epoch of 
 their formation no important change has taken place in 
 either the one or the other. The finer beds, though other 
 materials occasionally occur, are largely, sometimes almost 
 exclusively, composed of grains of quartz and of felspar 
 identical in every respect with those of the underlying 
 series. It may be a fact of some significance, for it agrees 
 with what I have elsewhere noticed in very old f ragmental 
 rocks, that the felspar appears to have been broken off 
 from the parent rock while still undecomposed, and in 
 many cases is even now remarkably well preserved. It 
 would seem, therefore, as if the denudation of the granitoid 
 rock had been accomplished without material decomposition 
 of its felspar ; but I must not allow myself to digress into 
 speculations on this interesting and suggestive fact." 
 
 The Torridon Sandstone has not, however, been entirely 
 derived from the Archaean gneiss. Mr. B. N. Peach states 
 that in some parts of Sutherland the basal conglomerate 
 consists chiefly of stones derived from older sedimentary 
 rocks, such as greywacke, quartzite, hardened shales, and 
 cherty limestones, together with a few pebbles of slaggy 
 diabase lava. 
 
 Professor Judd remarks 2 : " These rocks in their cha- 
 
 1 Pres. Address to Geol. Sec. of Brit. Assoc., 1886. 
 
 2 Pres. Address to Geol. Sec. of Brit. Assoc., 1885. 
 
22 PALAEOZOIC TIME. [CHAP. II. 
 
 racters and their relations so greatly resemble the Sparag- 
 mite Formation of Scandinavia, that it is impossible to 
 refrain from drawing comparisons between them. The 
 Scandinavian formation, however, includes calcareous and 
 slaty deposits, which are wanting in its Scottish analogue ; " 
 and he points out that as Upper Cambrian fossils have 
 been found at the very top of the Sparagmite series, this 
 fact lends support to the view that the Torridon Sandstones 
 are of Lower Cambrian age. 
 
 2. Geographical Restoration. 
 
 The relations which the Cambrian sediments bear to the 
 underlying Archaean, both in this country and elsewhere, 
 are so remarkable that we are driven to conclude that the 
 physical conditions of the earth's surface at this early 
 period of its history were very different from that which it 
 subsequently acquired. At the commencement of what 
 we call the Cambrian period, the surface of the earth seems 
 to have been extraordinarily rugged and uneven, exhibiting 
 a series of lofty mountain ridges separated by deep troughs 
 and hollows, the bottoms of which were 10,000 or 12,000 
 feet below the summits of the ridges. 
 
 How such inequalities were formed is a difficult question 
 to answer. Were they the result of the mode in which the 
 Archaean rocks were originally formed, or were they partly 
 the result of rain and rivers acting on a newly-formed 
 crust ? The conglomerates and coarse sandstones which are 
 so frequent in the Lower Cambrian series, and the un- 
 weathered state of the felspar grains in the grits, are sug- 
 gestive facts, aud one cannot help thinking that these rocks 
 must have been accumulated with much greater rapidity 
 than could be effected by any modern process of formation. 
 An obvious speculation suggests itself: Are we looking 
 
CHAP. II.] CAMBRIAN PERIOD. 23 
 
 upon the result of the first condensation of water upon the 
 earth's surface, and was the Cambrian sea the first great 
 body of water that ever lay over the European area ? It 
 must be admitted that there are some grounds for so think- 
 ing ; there may have been lower levels and older oceans in 
 other parts of the world, but so far as we know the Cam- 
 brian rocks are the oldest aqueous deposits in Europe, and 
 the Caerf ai beds of South Wales contain the oldest remains 
 of invertebrate animals ; moreover, though these animals 
 are certainly the ancestors of modern marine species, the 
 waters of the Cambrian sea may not have been salt ; and 
 we have no proof that these creatures had been differen- 
 tiated into salt- and fresh-water forms until we reach the 
 close of the Devonian period. 
 
 Dr. Hicks has discussed the general geographical condi- 
 tions of the Cambrian period, 1 and he thinks that the 
 higher parts of the pre-Cambrian land lay toward the 
 north-east of Europe, and that the surface had a general 
 slope from north-east to south-west, but was traversed by 
 mountain ridges having a general E.N.E. and W. S.W. 
 direction. If this were so, and subsidence took place, 
 the part of the surface which faced south-west would 
 first become covered by the sea. He infers from a consi- 
 deration of the Cambrian series in various parts of Europe 
 that the sea gradually spread further and further to the 
 north-east, and that there was a difference in level of 
 15,000 feet between the low ground of the south-west and 
 the high ground in Russia. 
 
 The late Professor Linnarsson, however, entirely differed 
 from Dr. Hicks. He points out 2 that the Scandinavian 
 succession goes nearly, if not quite, as low as that of South 
 Wales, and further that, though the sandstones below the 
 Scandinavian Menevian are not so thick as the British, this 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxxi., p. 552. 
 
 2 " Geol. Mag./' 1876, p. 145. 
 
24 PALAEOZOIC TIME. [CHAP. II. 
 
 may have been mainly due to a less rapid rate of deposi- 
 tion. " If Mr. Hicks' views of the physical geography of 
 the Cambrian period were correct, there ought to be in 
 the middle and upper portions of the Swedish series many 
 signs of littoral conditions. . . . The facts, however, rather 
 tend to show that most of the Swedish Cambrian rocks 
 were deposited in a deeper sea and farther from land than 
 the British." 
 
 The fact is that in Scandinavia, as in Britain, there are 
 great variations in the thickness of the Lower Cambrian 
 rocks ; thus in Norway the lowermost sandstones are 2,000 
 feet thick, while in Sweden they are only 100 feet. Again, 
 the Olenus beds in Norway contain sandstones and quart- 
 zites, but in Sweden they are wholly shales with bands of 
 limestone. These facts point rather to the conclusion that 
 the greatest mass of land lay to the north-west, for coarse 
 sediments are likely to thicken in the direction of land and 
 not away from it, as Dr. Hicks seems to suppose. The 
 Russian succession is not antagonistic to this conclusion, 
 for the whole Cambrian series is not 700 feet thick ; the 
 basal sandstones are 300 feet, and the overlying beds are 
 such as would be formed at a distance from land, being 
 blue clays surmounted by glauconitic shales and limestones 
 like some of our Cretaceous beds. 
 
 All the available evidence certainly seems to favour the 
 view taken by Professor Hull, 1 that the greater mass of dry 
 land lay to the north-west of Europe, and occupied a large 
 part of what is now the North Atlantic Ocean. There may 
 have been smaller but still extensive tracts of land of the 
 European area, as is plainly indicated in England and 
 Bohemia ; nay, it would appear that in Lower Cambrian 
 times there was in Europe more land than sea, and that 
 the subsequent changes throughout the Upper Cambrian 
 and Ordovician periods tended to reverse this state of things 
 1 " Physical History of the British Isles," p. 61. 
 
CHAP. II.] CAMBRIAN PERIOD. 25 
 
 by continued subsidence, which broadened the sea-spaces 
 at the expense of the land. 
 
 In dealing specially with the geographical conditions of 
 the British area, I have sought the assistance of Dr. Calla- 
 way, whose studies of the Cambrian rocks are well known, 
 and he has kindly furnished me with an outline of such in- 
 ferences as he thinks it is safe to draw in the present state 
 of our knowledge. These are as follows : 
 
 " The ideal reconstruction of the geography of any past 
 epoch is always a rather speculative task, but it becomes 
 especially difficult when we revert to a period so ancient as 
 that of the Lower Cambrian or Longmyndian. We can 
 learn little about tracts which are covered by post-Cam- 
 brian deposits, and the deep borings of the south-east of 
 England give us no help. We can, however, determine 
 the approximate position of some of the land masses which 
 rose amidst the waves of the Longmyndian sea. 
 
 "The groups of volcanoes which in later Archaean times 
 had spread out their lavas and ashes over so large a part 
 of England and Wales were extinct at the commencement 
 of the Cambrian period, but it would seem that several 
 mountain chains, some of them crowned like the Andes or 
 the Eocky Mountains by numerous volcanic cones, stood 
 above the waves. Dry land probably extended over what 
 are now the counties of Shropshire, Staffordshire, Leicester- 
 shire, Warwickshire, and Worcestershire, at least as far 
 south as Malvern, but how far this land stretched to the 
 north, east, and south, we have no means of knowing ; it 
 can only be said that analogy points to its having had a 
 considerable north-east and south-west extension. 
 
 " The preponderance of coarse sandstones indicates a 
 rapid submergence of the neighbouring land, and the basal 
 conglomerates in Wales indicate the gradual advance of 
 the waves over a sinking shore. The rapid thinning-out of 
 the Cambrian strata toward the west suggests that in the 
 
26 PALAEOZOIC TIME. [CHAP. II. 
 
 sea which now separates Wales from Ireland, land must 
 then have predominated. Parts of Carnarvon and Anglesey 
 are all that remain of the eastern side of this vanished 
 country. 
 
 " Beyond this there may have been another sea or gulf if 
 the rocks in the east of Ireland are rightly referred to the 
 Cambrian ; but it is a significant fact that no deposits of 
 Cambrian age have been found in any part of central or 
 northern Ireland, or in any part of Scotland, except, per- 
 haps, in Ross and Sutherland. It is rather unlikely, if any 
 considerable part of these areas had been under water in 
 Cambrian times, that every remnant of the deposits then 
 formed should have been since either swept away or covered 
 in. The balance of probability, therefore, is in favour of 
 the conclusion that land masses of considerable size lay to 
 the north and west of what is now G-reat Britain, and 
 formed a Cambrian Atlantis, of which a part of Norway, 
 the Hebrides, Donegal, and the highlands of Connemara 
 are the worn and inconspicuous remains." 
 
 To these remarks it is only necessary to add that at the 
 close of the Cambrian period the sea had gained very 
 largely on the land, that the tract of land indicated as 
 existing over central England was entirely submerged, and 
 that the promontory or island between Wales and Ireland 
 was probably reduced to very narrow limits, though parts 
 of it seem still to have remained above the sea-level. The 
 entire absence of Upper Cambrian rocks, so far as is yet 
 known, in northern Ireland and northern Scotland, seems 
 to justify the supposition that these areas remained in the 
 condition of land throughout the Cambrian period. The 
 Torridon sandstone may have been formed in a narrow 
 gulf penetrating into this land, or else, as Sir A. Ramsay 
 has suggested, in an inland freshwater lake. 
 
CHAPTEE in. 
 
 ORDOVICIAN PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 TjlNGLAND. The most southern area of Ordovician 
 -*-^ rock in England is a small tract on either side of 
 Dodman Head on the east coast of Cornwall. The rocks 
 exposed consist of brown grits, quartzites, slates, and ash- 
 beds, with some conglomerates, and they contain fossils 
 of Bala age, but as their base is not visible it is impossible 
 to draw any certain inferences as to the neighbourhood of 
 land. It is true that Mr. G-od win -Austen has called the 
 conglomerates " shingle-beds," ] and infers that they were 
 formed in close proximity to a coast-line, but Professor 
 Sedgwick describes them as trappean and schistose con- 
 glomerates, and speaks of their passing into " schaalstein" 
 and " trap shale " (i.e. volcanic ash), so that they hardly 
 seem to warrant the inference drawn by Mr. Austen. 
 
 At Malvern there is a total absence of Ordovician strata, 
 the Upper Cambrian shales being unconformably covered 
 by Silurian, but as the former dip under the latter, it is 
 possible that Ordovician rocks exist beneath the Silurian 
 area to the westward, and it would not, therefore, be safe 
 to infer that the Malvern area was land throughout Ordo- 
 vician times, though it will be seen from the sequel that 
 land did then exist over the centre of England, and it is 
 
 1 " Quart. Journ. Geol. Soc.," vol. xii. p. 44. 
 
28 PALEOZOIC TIME. [CHAP. III. 
 
 quite possible that the Malvern Hills were part of the 
 southern border of this land. 
 
 The larger part, if not the whole, of Wales formed part 
 of the Ordovician sea, and in this area the Cambrian sedi- 
 ments are succeeded by a thick series of comparatively 
 deep-water rocks, though they certainly were not formed 
 at any great distance from land. The succession consists 
 of (1) the Arenig series black slates and flags, from 3,000 
 to 4,000 feet thick, with the addition of much volcanic 
 material in the north-west of Wales; (2) the Llandeilo 
 series another group of black slates and nags, with a thin 
 limestone, in South Wales ; (3) the Bala series a more 
 variable group, consisting of shales and sandstones, with 
 two bands of limestone, the whole from 4,000 to 6,000 feet 
 thick. 
 
 As these Ordovician strata occur in full force on both 
 sides of the Pembrokeshire Archaean axis, it is probable 
 that this was completely submerged and covered by these 
 sediments. 
 
 In Shropshire the same complete series is found on the 
 western side of the Longmynd ridge, but in the Caradoc 
 district, on the eastern side of that ridge, the Arenig 
 and Llandeilo series are absent, sandstones of Bala age, 
 having a conglomerate at their base, resting on the local 
 representative of the uppermost Cambrian. 
 
 Fig. 1 is an ideal section, drawn for the purpose of 
 showing the possible underground geology of the midland 
 counties, for it is absolutely necessary to form some con- 
 ception of this before we can draw any inferences regarding 
 the probable position and extent of the land area which 
 seems to have existed over the centre of England in Ordo- 
 vician times. From the section it is seen that the Caradoc 
 sandstones are supposed to thin out beneath the Silurians 
 against the pre-Cambrian rocks, and that there is reason 
 to suppose that they were never deposited over that part of 
 
K-ll 
 
 ,11' 
 
 f " 
 
30 PALEOZOIC TIME. [CHAP. III. 
 
 Staffordshire which is traversed by the section, nor over 
 Warwickshire, where Coal-measures rest on Cambrian 
 shales. We may assume, therefore, that this district was 
 dry land during the whole of Ordovician time, that the 
 Longmynd and Caradoc tracts formed part of the land 
 area in Arenig and Llandeilo times, but were submerged 
 toward the close of the period, and covered by the Caradoc 
 sandstones and shales. The fact of quartz-felsite, like that 
 of Charnwood, having been found below the Lias near 
 Kettering, seems to indicate that this land tract had a still 
 further eastward extension. 
 
 In Anglesey and Carnarvon the pre-Cambrian ridges 
 which formed land throughout Cambrian times were still 
 further submerged, and, perhaps, eventually were over- 
 topped by the waves of the Ordovician sea. The exact age 
 of the earliest fossiliferous deposits of Anglesey is not yet 
 quite settled, but the probability is that the fossils in the 
 lowest grits are not of earlier date than the Arenig, and 
 Dr. Callaway thinks that at this time the northern and 
 central parts of the island were still above water. 
 
 " The basement conglomerates contain not only boulders 
 from the granitoidite, but also pieces of halleflinta, such as 
 we find east of Llanfaelog, and numerous fragments of 
 purple and green shale, very similar to types characteristic 
 of the tract west of Malldraeth Marsh. . . . The western 
 area furnishes similar evidence; the large angular frag- 
 ments in the Tywyn conglomerate cannot have travelled 
 far, and the pieces of altered shale in the Clymwr conglo- 
 merate must have been derived from the neighbouring land 
 to the west." l In other parts of the island beds of Bala 
 age have been found, and these probably extended much 
 farther west, and were, perhaps, continuous with beds of 
 the same age in the west of Ireland. 
 
 In the Lake District we again find a thick series of 
 1 Callaway in " Quart. Journ. Geol. Soc.," vol. xl. p. 582. 
 
CHAP. III.] ORDOVICIAN PERIOD. 31 
 
 muddy deposits representing the lower part of the Ordo- 
 vician system that part of the Skiddaw slates which 
 underlies the grit-beds of Gatesgarth and Latterbarrow 
 being 4,000 or 5,000 feet, and that above these grits being 
 no less than 7,000 feet thick. These are succeeded by an 
 immense series of lavas and ash-beds with interbedded 
 slates (the Borrowdale series, estimated at 12,000 feet), 
 above which are limestones and shales, which correspond 
 to the upper part of the Bala group of Wales. 
 
 With regard to the Skiddaw series, Mr. J. C. Ward l re- 
 marks that the grits in the lower part of the series thicken 
 to the westward, whence he infers that continental land 
 lay in that direction. The water in which the material of 
 the slates subsided was probably never very deep, and 
 there must have been a long-continued depression of the 
 area to allow of so thick an accumulation of sediment. 
 Mr. Ward states that in the south-west of the district the 
 volcanic forces came into play much earlier than they did 
 to the north-east. It is also known that in some places the 
 Limestone group rests unconformably on the volcanic 
 series. 
 
 The following paragraphs are quoted from Mr. Ward's 
 paper. The observed facts " all point to volcanic action 
 commencing at the close of the so-called Skiddaw slate 
 period beneath the waters of the sea, and the gradual pas- 
 sage from submarine volcanic conditions to those of ter- 
 restrial and wholly subaerial volcanoes. 
 
 "The centres of eruption are difficult to fix upon, as 
 might be expected amongst volcanic remains of such anti- 
 quity. The boss of Castle Head, Keswick, almost certainly 
 represents one such centre, and the best developments of 
 lava flows are all found occurring within easy distance. . . . 
 What the height of the old Cumbrian volcano or volcanoes 
 may have been it is difficult to estimate, but volcanic de- 
 1 "Geol. Mag.," 1879, p. 51. 
 
32 PALEOZOIC TIME. [CHAP. III. 
 
 posits were accumulated to a thickness, in parts, of at least 
 12,000 feet, and the highest beds known are unsucceeded 
 by any conformable series of sedimentary rocks ; hence we 
 know not how much of the products of the old volcano has 
 been lost, and for aught we know to the contrary, an Etna 
 in size may once have stood where now are the resting- 
 places of quiet lakes." 
 
 When volcanic activity had ceased, " a subsidence of the 
 region ensued, accompanied doubtless by much waste of 
 the volcanic material through the agency of atmospheric 
 denudation. Subsidence, however, continued until the old 
 volcano came within the planing power of marine coast- 
 action, and at last there was probably but little of the old 
 terrestrial volcano left above the level of the sea." As the 
 waters gradually crept over the site of the volcanic distur- 
 bances the calcareous sediment which was being deposited 
 on the surrounding sea-bottom gradually enveloped and 
 covered the surface of the sinking volcanic area. That this 
 sea covered the greater part of northern England is known 
 from the existence of Ordovician rocks in Teesdale and 
 near Ingleborough. 
 
 Scotland. In the south of Scotland Ordovician rocks are 
 known to occupy large areas, and they have been mapped 
 by the Geological Survey, but little information has yet 
 been published about them. There are, in fact, only two 
 districts where the vertical succession has been ascer- 
 tained, viz., Girvan in Ayrshire, and Moffat in Dumfries, 
 and our knowledge of these is almost entirely due to the 
 careful investigations of Professor Lap worth. 
 
 It so happens that though the same succession of fossils 
 can be traced in each area, yet the characters and thick- 
 nesses of the beds containing them differ enormously, the 
 Girvan strata being over 3,000 feet thick, while those of 
 Moffat are only 150. 
 
 In the Girvan area there are shales of Arenig age, but 
 
CHAP. III.] ORDOVICIAN PERIOD. 33 
 
 they are so entangled among igneous and metamorphic 
 rocks that their stratigraphical relations have not yet been 
 made out. Moreover, it appears certain that there is a 
 marked unconformity between the igneous group, or Bal- 
 lantrae rocks, and the succeeding deposits of Upper Llan- 
 deilo age. At the base of the latter is a coarse purple 
 conglomerate containing fragments of the Ballantrae rocks, 
 and we may therefore conclude that land existed in this 
 area during the greater part of the Arenig and Llandeilo 
 periods. Moreover, the base of the Bala series is a con- 
 glomerate 500 feet thick, which overlaps the Llandeilos on 
 to the older rocks, so that some land was then still above 
 the sea-level, but this was soon submerged, and the subsi- 
 dence continued throughout the Bala period till a thick- 
 ness of 3,300 feet of deposits had been laid down. 
 
 That the land thus indicated did not extend far in a due 
 easterly direction seems probable from a consideration of 
 the Moffat section ; here no base is exposed, but the small 
 thickness and uniform shaly character of the deposits, 
 taken together with the rarity of any organic remains ex- 
 cept graptolites, lead us to infer that these shales were 
 formed at some distance from land and in comparatively 
 still and deep water. It is possible that the land may 
 have had a south-westerly prolongation into the north of 
 Ireland, but the base of the Ordovician is not there seen, 
 and consequently there is no actual evidence for this sup- 
 position. 
 
 With regard to the northern part of Scotland, it is only 
 quite recently that its structure has been properly under- 
 stood. Messrs. Lapworth and Callaway were the first to 
 establish the true upward succession, and to show that it 
 was in many places inverted by the complete overthrow of 
 the strata. Their work has been continued by the officers 
 of the Geological Survey, and the succession in Durness 
 and Eriboll is given as follows, in descending order : 
 
 D 
 
34 PALEOZOIC TIME. [CHAP. III. 
 
 4. A great limestone series, believed to be over 1,400 feet thick. 
 
 3. Calcareous grits and mudstones, about 80 feet. 
 
 2. Fine-grained quartzites, with worm casts, 300 feet. 
 
 1. Coarse quartzites, with a thin conglomerate at the base, 200 feet. 
 
 Many fossils occur in the limestones, and so far as they 
 are yet known it seems probable that the beds are of the 
 same age as the Orthoceras limestone of Sweden and the 
 Trenton limestone of Canada, viz., Upper Arenig or Lower 
 Llandeilo. 1 If this is so, the basement beds can hardly be 
 older than the Arenig of Wales. No break or overlap 
 appears to exist in the series, but the group as a whole 
 rests un conformably on the older rocks, lying partly on 
 the Torridon sandstone, and partly on the Archaean gneiss. 
 
 The succession above mentioned plainly indicates the 
 gradual subsidence of a land surface and its submergence 
 beneath an increasing depth of water. Mr. B. N. Peach 
 draws the following inferences from the characters of the 
 rock : 3 "In the case of the basal quartzites, where we 
 have a passage from a land surface to a sea-bed, there is 
 little or no organic matter mixed with the coarse siliceous 
 sand, which from its coarse texture, and the false-bedding 
 of the layers, bears evidence of rapid accumulation. There 
 would therefore be no food for the support of Ann elides 
 under these conditions. But with the slower accumulation 
 of sediment indicated by the 'pipe-rock,' there was evi- 
 dently time for the fertilization of the sand by the shower 
 of minute pelagic organisms which is ever falling on the 
 sea-floor, so that it could afford food for the burrowing 
 annelids, whose casts now form the stony 'pipes.' . . . 
 As the sea-floor gradually subsided, the shore-line was re- 
 moved farther from the area of deposit, and hence during 
 the deposition of the 'fucoid beds' only the finest sedi- 
 
 1 See J. W. Salter, " Quart. Journ. Geol. Soc.," vol. xv. p. 381, and 
 J. E. Marr, "Classif. of Cambrian and Silurian Rocks.," 1883, Cam- 
 bridge, p. 67. 
 
 2 " Proc. Roy. Phys. Soc. of Edinburgh, 1886," vol. ix. pt. i. p. 4. 
 
CHAP. III.] OEDOVICIAN PERIOD. 35 
 
 ment derived from the land was mingled with the calcareous 
 and organic matter." 
 
 " After the deposition of the Serpulite grit hardly any 
 sediment derived from the land entered into the composi- 
 tion of the overlying limestones, and eventually nothing 
 seems to have fallen on the sea-floor but the remains of 
 minute organisms, whose calcareous and siliceous skeletons 
 slowly built up the great mass of limestone and chert so 
 conspicuously displayed at Durness." 
 
 Ireland. There are five principal districts in Ireland 
 where Ordovician rocks occur : (1) Wicklow, Wexford, and 
 Waterford; (2) Clare and Tipperary; (3) South Ulster- 
 Down, Armagh, &c. ; (4) North Ulster Donegal and Lon- 
 donderry ; (5) G-alway and Mayo. Between 1 and 3 
 are two small but important exposures, that on the Dublin 
 coast at Portraine, and the ridge known as the Chair of 
 Kildare. 
 
 No Irish rocks have yet been identified by their fossils as 
 contemporaneous with the Welsh Arenig. Wherever the 
 base is seen in the east of Ireland, beds with Llandeilo 
 fossils rest unconformably on metamorphic rocks, which 
 are classed as Cambrian. Coast sections near Bannow 
 and Greenore Point in Wexford expose the basement beds, 
 which are purple conglomerates and sandstones overlain 
 by black shales with Llandeilo fossils, a succession which 
 recalls that of the Girvan district in Ayrshire. The Dark 
 Shale series (Llandeilo) may have a thickness of 2,000 or 
 3,000 feet, and it is surmounted by an equal thickness of 
 grey and greenish shales with interstratified igneous rocks, 
 the slates containing fossils of Bala types. 
 
 The Portraine section is remarkable for the resemblance 
 of the rocks to the upper part of the Cumberland Ordovi- 
 cian system, i.e. the Coniston Limestone and the underlying 
 Borrowdale .group, with its lavas and ash-beds. There 
 can be little doubt that this area was the centre of similar 
 
36 PALEOZOIC TIME. [CHAP. III. 
 
 volcanic disturbances, followed by similar conditions of 
 sedimentation, as in the case of the Cumbrian district 
 already described (p. 32). A third centre with a similar 
 sequence is found in the Chair of Eildare on the same line 
 of strike, and other tracts of Ordovician rocks occur still 
 further south-west, in the mountains of Clare and Tip- 
 perary. 
 
 In South Ulster we have a continuation of the South 
 Scottish Ordovicians, and the succession, so far as it is 
 known, is similar ; the base is not seen, but certain shales 
 have yielded the graptolites of the Glenkiln group (Llan- 
 deilo), and others contain Bala fossils, while at Pomeroy, 
 in Tyrone, there is a limestone from which many Bala 
 fossils have been obtained. 
 
 In Mayo and Galway there are shales which are believed 
 to be of Llandeilo age, and others which contain the cha- 
 racteristic fossils of the Bala rocks ; they are estimated at 
 several thousand feet, but the stratigraphy of this part of 
 Ireland requires further investigation. 
 
 2. Geographical Restoration. 
 
 5 From the foregoing facts it would appear that the sub- 
 mergence which began in Cambrian times continued, during 
 the formation of the Arenig series, over the whole of the 
 western and northern portions of the British area, but 
 that over a certain space in the centre of the sea which 
 covered England there was an upward movement resulting 
 in the appearance of an island composed of Archaean and 
 Upper Cambrian rocks. In an east and west direction 
 this island seems to have had a length of at least eighty 
 miles, stretching from the Longmynd in Shropshire to 
 Charnwood Forest in Leicestershire and the neighbourhood 
 of Kettering, and possibly even further to the east. Of its 
 northerly extension we can predicate nothing at present ; 
 
PLATE I. HYPOTHETICAL RESTORATION OF EARLY ORDOVICIAN GEOGRAPHY 
 (ARENIG EPOCH). 
 
CHAP. III.] OEDOVICIA.N PEBIOD. 37 
 
 it is not at all unlikely to have stretched some distance 
 to the north-east, but I have not ventured to indicate such 
 an extension on the map. Southward it probably sent a 
 promontory as far as Malvern, but its southern boundary 
 is as uncertain as its northern limit. 
 
 West of this island there seems to have been another 
 formed by the unsubmerged portion of the ridge spoken of 
 in the last chapter as reaching across from Anglesey to the 
 south-east of Ireland, but how much farther to the west 
 and south it extended at this time we have no means of 
 knowing, so that the tract shown on the map may be re- 
 garded as the minimum amount of land in this region. 
 
 It is difficult to say how much of Ireland may have been 
 land in Arenig times, because we do not yet know whether 
 any Arenig beds exist in that country or not, but they 
 certainly seem to be absent in Wicklow and Wexford, and 
 they have not been identified elsewhere. If the meta- 
 morphic rocks of Mayo and Galway are Archaean, and the 
 Llandeilo shales rest upon them with an entire absence of 
 Cambrian and Arenig beds, we may suppose that this part 
 of the Archaean surface was not submerged till after the 
 beginning of the Ordovician period. How far this land 
 extended eastward in Upper Cambrian and Arenig times 
 is a point of very great interest when viewed in connection 
 with the great differences which exist between the Arenig 
 rocks of England and those of northern Scotland. 
 
 The similarity of the Durness and Trenton limestones 
 and the American aspect of the fauna found in the former 
 have suggested to Mr. Peach that " some old shore-line or 
 shallow sea must have stretched across the North Atlantic 
 or Arctic Oceans, along which the forms migrated from one 
 province to the other, and that some barrier must have cut 
 off this area from that of Wales and central Europe." l 
 He might have supported this suggestion by a reference to 
 1 " Address to the Roy. Phys. Soc., Edinburgh, 1886," p. 7. 
 
38 PALEOZOIC TIME. [CHAP. III. 
 
 the opinion expressed by Sir R. Murchison, that a large 
 part of the Arctic region was land in Lower Silurian times, 
 because no rocks of that age had been discovered there. 
 Nor have any been found since this opinion was expressed, 
 though (Upper) Silurian rocks cover large areas in the 
 north-western part of the Arctic Archipelago. 
 
 It seems probable, therefore, that the great northern 
 continent of early Cambrian times was partially broken up 
 by the submergence which ensued, and that an open sea 
 extending from North America to Scotland and Scandinavia- 
 was established for the first time at the beginning of the 
 Ordovician period; that this sea' divided the Cambrian 
 continent into two parts, the larger part lying over Green- 
 land and the northern regions, while a smaller mass lay to 
 the south, and stretched eastward through the north of 
 Ireland and into the south of Scotland, so as to separate 
 the northern sea from that which lay over the European 
 area. The thick conglomerates of Llandeilo and Bala age 
 which occur in the Girvan district may indicate a part of 
 its southern border, but of its northern shore we have 
 absolutely no evidence at present. Mr. J. E. Marr takes a, 
 somewhat similar view, 1 and has suggested the existence of 
 a ridge of pre-Cambrian land across the centre of Scotland 
 in Arenig times, separating the sea in which the Orthoceras; 
 and Durness limestones were formed from that of the 
 Girvan area. It is possible, therefore, that the land barrier 
 had a still further eastward extension, but until more is 
 known of the geology of the central Highlands this must 
 remain uncertain, and the form given to the land in the 
 accompanying map is of course merely a suggestion based 
 upon the preceding considerations. The map is in fact only 
 a pictorial representation of the theory suggested by the 
 facts which are known to us, and may require considerable 
 modification as our knowledge increases, and the same may 
 1 "Classif. of Camb. and Sil. Rocks," p. 68. 
 
CHAP. III.] ORDOVICIAN PERIOD. 39 
 
 be said of the succeeding restorations of Palaeozoic geo- 
 graphies, so little do we really know of these rocks and 
 their extension beneath the British Islands. 
 
 During the deposition of the Llandeilo and Bala rocks 
 depression continued, and the whole of the British area 
 seems to have been submerged, with the exception of a 
 portion of the central English island ; the dimensions of 
 this island were of course considerably diminished, as 
 testified by the extension of the Caradoc sandstones to the 
 east of the Longmynd, but these do not extend into 
 Staffordshire or Warwickshire. Llandeilo and Bala rocks 
 seem to have been laid down over the whole of Ireland, 
 and if any part of the land barrier above mentioned re- 
 mained above water it must have been outside the present 
 limits of Ireland. 
 
 Numerous volcanic islands, however, came into existence 
 during this period, and portions of the lava-streams which 
 they emitted are interbedded with the sedimentary rocks 
 of Llandeilo and Bala age. In Llandeilo times a line of 
 such islands seems to have stretched across Ireland and the 
 north of England in a south-west and north-east direction, 
 while in Bala times great eruptions took place from a 
 group of volcanoes in Wales and the east of Ireland. 
 
 The period was brought to a close by an upheaval which 
 brought up the submerged ground, but gave it a different 
 outline and extension from that which it possessed in 
 Arenig times. 
 
CHAPTEE IV. 
 
 SILURIAN PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 COMMENCING- with what is usually regarded as the 
 typical Silurian district, it may be stated that the 
 Silurian rocks form a continuous escarpment through 
 Shropshire and the east of Wales, and that they rise to the 
 surface at intervals in the counties of Gloucester, Mon- 
 mouth, Hereford, and Stafford. 
 
 The lowest beds in this district are sandstones, shales, 
 and conglomerates ; this (Llandovery) division is thickest 
 in the western part of the area, and is there divisible into 
 two groups, with a combined thickness of nearly 2,000 
 feet, but the upper stage frequently overlaps the lower, 
 and it is the only one found in the more eastern outcrops, 
 where they include beds of conglomerate ; these basal con- 
 glomerates vary much in thickness, and sometimes overlap 
 the Ordovician strata, as in the Longmynd and Malvern 
 areas, where they rest upon the Cambrian rocks. 
 
 The Llandovery sandstones are succeeded by a great 
 series of dark grey shales, in which limestones are developed 
 at intervals ; some of these limestones attain a thickness 
 of 100 feet, but they are all lenticular deposits, and it is 
 often difficult to identify the beds seen in one detached 
 area with those which occur in the others. Only three of 
 these limestone bands have received distinctive names, 
 
CHAP. IV.] SILTTBIAN PERIOD. 41 
 
 these being respectively, in upward succession, the Wool- 
 hope, the Wenlock, and the Aymestry limestones, but at 
 Tortworth, May Hill, and Malvern, there is a fourth lime- 
 stone between the Wenlock and the representative of the 
 Aymestry, which might be regarded as a distinct horizon. 
 This great shale and limestone series is from 2,000 to 3,000 
 feet thick. 
 
 The highest Silurian beds in this region consist of yellow 
 sandstones and reddish shales, the latter passing up into red 
 laminated micaceous sandstones and marls, some of which 
 contain marine fossils; these beds form a passage from 
 Silurian to Old Eed Sandstone, and were evidently formed 
 in shallower water than the dark mudstones and lime- 
 stones of the Wenlock series. 
 
 As regards the eastward extension of the Silurian rocks 
 very little is yet known ; the most easterly outcrop is near 
 Walsall and Barr in South Staffordshire, but Wenlock 
 shales have been found below the cretaceous rocks in a 
 deep boring at Ware, near Hertford, so it is probable that 
 they have a wide subterranean extension beneath the south 
 and east of England. 
 
 The subdivisions which have been established in the 
 limited area where the Silurian rocks were first described, 
 will not apply to the rocks of the same age outside that 
 area. When traced in any westward direction, a great 
 change takes place in the lithological character of the 
 strata : all the limestones thin out and disappear, and the 
 soft mudstones change into a series of hard shales, flags, 
 and grits. In central and northern Wales these alter- 
 nations of shales and sandstones attain a thickness of 
 from 5,000 to 7,000 feet, and this change suggests the 
 existence of a considerable mass of land to the westward. 
 
 The Silurian rocks of the Lake District are similar to 
 those of North Wales they have a conglomerate at the 
 base which lies unconformably upon Ordovician rocks, and 
 
42 PALEOZOIC TIME. [CHAP. IV. 
 
 to this succeeds an immense series of shales, grits, and 
 flags, which are no less than 13,000 feet thick. Of this 
 total only 250 feet belong to the lower or Valentian group, 
 the great mass of the beds (11,000 feet) representing 
 the Salopian shale and limestone group, while the upper 
 2,000 feet represent the red passage beds of the Welsh 
 border. Although no Upper Silurian beds are found in 
 Cumberland north of their Coniston and Windermere out- 
 crop, yet they set in again on the north side of the Solway, 
 and, as the late Mr. J. C. Ward writes, 1 " there is every reason 
 to believe that the whole series once extended over the now 
 exposed volcanic rocks, for there is nothing in the deposits 
 themselves to indicate a land margin near their present 
 outcrop. Such a thickness of beds as that just described 
 implies a continued subsidence of the sea-bed throughout 
 the whole period of deposition." 
 
 The prevalence of sandstones and flagstones, however, 
 shows that the water was never very deep or very far from 
 land, and we are guided to the direction in which some of 
 this land lay by considering the lithological changes which 
 the lowest group exhibits when traced in different direc- 
 tions. In Westmoreland it consists entirely of shale, with 
 a local conglomerate at the base ; to the south-east, near 
 Settle, it is represented by a band of calcareous mud- 
 stone resting on a few inches of grey shale, while to the 
 north and north-west it thickens into a great series of 
 shales and sandstones, which are spread over large areas 
 in the Southern Uplands of Scotland. 
 
 In the Moffat district (Dumfries) the Birkhill and Gala 
 groups must be several thousand feet thick, and consist 
 largely of hard sandy and micaceous flagstones, but without 
 any actual shore-beds or conglomerates. In Ayrshire, 
 however, near G-irvan, they include thick beds of conglome- 
 rate ; the basal bed of this district is a boulder conglome- 
 
 1 Geol. Mag.," 1879, Dec. 2, vol. vi. p. 55. 
 
CHAP. IV.] SILURIAN PERIOD. 43 
 
 rate about seventy-five feet thick, consisting of rounded 
 pebbles and boulders in a matrix of purple sand, and it 
 passes up into soft sandstones 250 feet thick. In another 
 locality these beds are absent, and rocks belonging to a 
 higher horizon rest unconfonnably on the Ordovician ; 
 again there is a basal conglomerate about fifty feet thick 
 and greenish in tint, " the main mass of this conglomerate 
 is made up of well-rounded boulders varying from one inch 
 to a foot and a half in diameter ; they consist of pieces 
 of granite, porphyry, felstone, greywacke, shale, Lydian- 
 stone, quartz, and jasper, embedded in a coarse sandy 
 matrix of a dark-green colour, and excessively.indurated." ] 
 Higher still is a band of quartz conglomerate succeeded by 
 a series of shales, grits, and flagstones, and the total thick- 
 ness of the Valentian here is estimated at about 1,800 feet 
 (exclusive of the Cyrtograpsus shale). 
 
 It is clear, therefore, that land existed in this G-irvan 
 district at the commencement of Silurian time, and that in 
 passing southward and eastward we recede from this land ; 
 the mass of the land must consequently have lain to the 
 north and north-west. 
 
 The higher Silurian groups are represented in the south 
 of Scotland by the Hawick and Kiccarton Beds, with their 
 equivalents, the Bargany and Stratton groups, in Ayrshire, 
 and finally, in Lanark and Edinburgh there is a series of 
 brown and grey beds with Wenlock and Ludlow fossils, 
 which are from 3,000 to 4,000 feet thick, and pass up into 
 the Lower Old Red Sandstone. We may conclude, therefore, 
 that a thick mass of Silurian strata once extended over the 
 whole area of the Southern Uplands, and passed beneath 
 the Lowlands of central Scotland. No Silurian rocks, 
 however, emerge from beneath the Old Eed Sandstone on 
 the northern border of the Lowlands, where this sandstone 
 rests unconformably on the Highland gneissic series; neither 
 1 Lapworth, " Quart. Journ. Geol. Soc.," vol. xxxviii. p. 638. 
 
44 PALEOZOIC TIME. [CHAP. IV. 
 
 is any area of Silurian rock known to exist in northern 
 Scotland. So far, therefore, as we can judge from present 
 evidence, the Silurian rocks probably die out beneath the 
 Lower Old Red on the south side of the great boundary 
 fault. 
 
 Passing now to Ireland, we find a significant absence of 
 Silurian rocks in the south-east of that country. The Ordo- 
 vician rocks of Dublin, Wicklow, and Wexford are flanked 
 by Upper Old Eed Sandstone and Carboniferous rocks a 
 sequence suggestive of these districts having been land 
 throughout the periods of the Silurian and Lower Old Eed 
 Sandstone. Rocks representing the Llandovery group occur 
 at several localities in eastern and central Ireland, as in 
 County Down, at Portraine in Dublin, and at the Chair of 
 Kildare, but the only complete sections of Silurian rocks 
 are found on the extreme western shores. In G-alway and 
 Mayo there is striking evidence of great physical changes 
 having taken place in the interval between the formation 
 of the Ordovician and Silurian rocks of Ireland. Here the 
 basement beds with Llandovery fossils rest on the edges of 
 upturned and metamorphosed Ordovician strata, so that 
 great terrestrial disturbances must have taken place, re- 
 sulting in the compression, metamorphisin, and upheaval 
 of the older series before the deposition of the Silurian 
 deposits, for the conglomerates contain fragments of these 
 underlying metamorphosed Ordovicians. 
 
 We may reasonably infer that the existence of the conti- 
 nental land which was postulated as existing to the north- 
 west of Ireland in Ordovician times had much to do with 
 the location of this pressure and metamorphism, and that 
 the terrestrial forces finally expended themselves in an 
 elevation and extension of the land which had previously 
 existed, bringing its boundaries farther south and within 
 the limits of what is now Irish soil. During subsequent 
 subsidence the coast-line again receded northward, and the 
 
CHAP. IV.] SILURIAN PERIOD. 45 
 
 Silurian conglomerates were deposited along its shores, 
 while the sand and mud that was worn from the detrition 
 of the land was carried eastward and spread over the 
 bottom of the neighbouring sea. 
 
 Silurian rocks occur also in Kerry, and include represen- 
 tatives of nearly the whole system, but the actual base is 
 not seen, while their upper limit is difficult to fix, as they 
 pass into a series of slates and grits which are litho- 
 logically similar to the beds below, but do not contain 
 fossils. 
 
 2. Geographical Restoration. 
 
 We have seen that nearly everywhere, but especially in 
 the north-west of Ireland, there was great disturbance and 
 upheaval at the commencement of the Silurian period ; 
 that this was followed by a gradual subsidence, during 
 which the materials gained from the land tracts were 
 quietly spread over the sea-bottom ; and that, finally, over 
 the English and Scottish areas, the incoming of sandstones 
 and the narrowing of the areas of deposition bespeak a 
 rapid elevation. 
 
 It will be best to consider the geographical conditions 
 which seem to have existed at the beginning of the period, 
 for we cannot say how much of the land areas remained 
 during the subsequent submergence. 
 
 The largest land tract seems to have been to the north 
 and north-west of the British Isles, and there is reason to 
 think that a continent of some size occupied a large part 
 of what is now the North Atlantic Ocean. No Silurian 
 rocks having been found in the northern parts of Scot- 
 land, it is probable that in early Silurian times the coast- 
 line of this continent ran through the north-west of Ire- 
 land and the centre of Scotland. The Ayrshire conglome- 
 rates were probably formed round an island, or possibly off 
 
46 PALEOZOIC TIME. [CHAP. IV. 
 
 a promontory jutting out from a main line of coast, but I 
 have not ventured to insert either on the map (PI. I.), as so 
 little is known of their lateral extent, and as yet they have 
 only been proved to occur over a small area. To the east 
 there was open sea, and the close correspondence between 
 the Scottish and Swedish zones of life leads us to infer 
 that the sea-bed was continuous from one region to the 
 other. 
 
 It is possible, however, that an island of considerable 
 size lay between Ireland and Wales, and included certain 
 areas which now form portions of these countries. The 
 lateral change which takes place in the character of the 
 Silurian strata as they pass westward from Shropshire, 
 and the thickening of the sandstones to the north-west, are 
 facts which indicate land in that direction. From the 
 quantity of felspar grains that enter into the composition 
 of the Denbigh grits, Sir A. Ramsay has inferred " that 
 part of the mountain region of North Wales between 
 Conway and Cader Idris then formed land (very different 
 from its present form), which in some degree contributed 
 locally to make these strata by the waste of the felspathic 
 lavas and ashes that form such a distinguishing feature of 
 the Lower Silurian rocks." ] If, however, the Ordovician 
 tracts of eastern Ireland were united to those of Wales, 
 and formed a continuous mass of land during part and, 
 perhaps, the whole of the Silurian period, there is no neces- 
 sity to suppose that the felspathic material was derived 
 from the Snowdon region in particular, since felspathic 
 lavas occur also in Wicklow and Wexford, and were doubt- 
 less exposed at many places over the intervening tract of 
 land. Northward this land may have extended as far as 
 the Isle of Man, and the conglomerates which occur in the 
 Sedburgh and Settle districts suggest the presence of 
 islands at its north-eastern end, but there can be little 
 1 " Geology of North Wales," second edition, p. 285. 
 
PLATE II. HYPOTHETICAL RESTORATION OF SILURIAN* GEOGRAPHY 
 (LLAM)OVERY OR V ALEUTIAN EPOCH). 
 
CHAP. IV.] SILTJEIAN PEEIOD. 47 
 
 doubt that they were soon deeply submerged and covered 
 by the Silurian sediments. 
 
 The evidence for the existence of this Hiberno- Cambrian 
 island is not at present very strong, but it furnishes us 
 with a means of accounting for the great thickness of 
 the Silurian deposits on its eastern side, for if we suppose 
 that the tidal currents came from the south-westward, a 
 reference to the map (PI. I.) will show that they would 
 naturally sweep the debris gained from the erosion of its 
 southern and western shores round to the more sheltered 
 side, and that great banks of sand and mud would be 
 likely to accumulate along the eastern shore and beyond 
 the north-eastern extremity ; the sea itself may originally 
 have been of considerable depth, and the continued sub- 
 mergence would prevent it from being entirely silted up. 
 
 There is better evidence for the existence of two smaller 
 tracts of land to the eastward, which may have been sepa- 
 rate islands, or may have been promontories from a larger 
 tract lying to the north-east of them. One of these was 
 formed by the rocks of the Longmynd and Shelve district ; 
 the Llandovery conglomerate wraps round the edges of 
 this tract, which doubtless had a farther extension to the 
 north-east in Silurian times beyond the range of the 
 Wrekin. The coasts of this island were probably rather 
 steep, and the sea, on the eastern side at any rate, was 
 deep, or limestones would not have been formed in such 
 near proximity. 
 
 * The other island was probably rather larger, and was 
 the remnant of that which seems to have existed over the 
 midland area in Ordovician times, but only the higher ridges 
 between Malvern and Charnwood Forest were left, and it 
 is impossible to say whether these remained above water 
 throughout the Silurian period. 
 
 It is probable, indeed, that both this and the Longmynd 
 island were surrounded by coral reefs which were built up 
 
48 PALEOZOIC TIME. [CHAP. IV. 
 
 around them as they sank beneath the Silurian sea, till 
 after existing for a time in the condition of atolls, they 
 were eventually submerged and buried under the higher 
 Silurian shales and mudstones. 
 
 It is just possible that another island existed to the 
 south-west of England, and included part of Cornwall, for 
 no rocks of true Silurian age have yet been found in that 
 county, and it is believed that the oldest Devonians rest on 
 the Ordovician rocks of Mevagissey and Veryan Bay. 
 Further examination of this district is required, however, 
 before any definite conclusions can be drawn. 
 
 Basal Silurians exist in Brittany, but nothing comparable 
 to our Wenlock and Ludlow series is found there, and 
 French geologists believe that during the latter part of the 
 Silurian period the Armorican and Cotentin region formed 
 an island the limits of which were very nearly those which 
 are now presented by the pre-Devonian rocks of this 
 district. 1 
 
 1 Lapparent, " Trait< de Geologie," second edition, p. 781. 
 
CHAPTER V. 
 
 OLD RED SANDSTONE AND DEVONIAN. 
 
 THERE is much uncertainty about the classification 
 and correlation of the rocks which intervene between 
 the Silurian and the Carboniferous systems, and this un- 
 certainty mainly arises from the fact that there is no 
 locality in Britain where an unbroken series of these inter- 
 vening rocks can be studied. In several areas the Silurian 
 is seen to pass upward into a series of red and purple 
 sandstones (Old Red Sandstone), but in every case there is 
 a break before the Carboniferous series is reached. Again, 
 there is one area (North Devon) where Carboniferous rocks 
 rest conformably on a series of strata containing a peculiar 
 fauna which stamps them as of intermediate age between 
 Silurian and Carboniferous, but the base of these (Devonian) 
 rocks is not seen, so that we do "not know what they rest 
 upon, and it is possible that a considerable thickness of rocks 
 intervenes between the Lower Devonian Sandstones and 
 the Silurians of Upper Ludlow type, if such beds exist 
 beneath North Devon. 
 
 The Old Red Sandstone is divided into a Lower and an 
 Upper Series, with a gap between them. The greater part 
 of the Devonian system was doubtless deposited during 
 the period which this gap represents, though its lowest 
 portion may have been coeval with part of the Lower Old 
 Red, and its uppermost portion is generally acknowledged 
 as the equivalent of the Upper Old Red. 
 
50 PALAEOZOIC TIME. [CHAP. V. 
 
 Since, however, we cannot be sure that the strata which 
 conformably succeed the Silurian are represented to any 
 great extent in the Lower Devonian group, and as it is 
 possible the mass of them may be older, the safest plan 
 will be to treat the rock- groups above mentioned as three 
 separate series, viz. : (1) Lower Old Eed Sandstone, and 
 its homotaxial equivalents in Scotland and Ireland; (2) 
 Devonian rocks ; (3) Upper Old Eed Sandstone. This is 
 the plan adopted by Mr. H. B. Woodward in his new 
 edition of the " G-eology of England and Wales." 
 
 1. Stratigraphical Evidence. 
 
 1. Lower Old Red Series. In England this series is 
 only found on the borders of Wales, in the counties of 
 Brecknock, Monmouth, Hereford, and Shropshire, where 
 it covers a considerable area. The rocks consist of sand- 
 stones, flagstones, and marls, the sandstones generally red, 
 the marls red, grey, or green, and including lenticular 
 masses or nodules of limestone, which are locally known as 
 " cornstones ; " hence the whole series is sometimes called 
 the " Cornstone Series," and its thickness is supposed to 
 be from 2,000 to 2,500 feet. It is succeeded by the Middle 
 Old Eed Sandstone, or "Brownstone Series," but Mr. 
 Symonds believes that there is a break in the succession 
 at the summit of the Cornstone group. 1 
 
 The limits of this group are not yet accurately known, 
 but its western outcrop is believed to extend from the 
 head-waters of the river Usk in Brecknock to Much Wen- 
 lock in Shropshire, and as it also flanks the Silurians of 
 Woolhope and Malvern, &c., it would appear to lie in a 
 broad synclinal which has a general north-east to south- 
 west strike. The area becomes narrower towards the north - 
 
 1 " Records of the Eocks," p. 234. 
 
>^PPK 
 
 MINIVER BIT* )j 
 
 CHAP. V.] DEVONIAN PEEIOD. \X C/\l | 51 
 
 east, and though it is doubtless continued for some distance 
 under the Shropshire Coalfield, it probably " noses out " 
 beneath the northern boundary of that county. 
 
 What its original limits were is a much more difficult 
 question, but it undoubtedly spread some distance westward 
 over the Silurian rocks of Brecknock, Radnor, and Shrop- 
 shire ; northwards it may have stretched through parts of 
 Denbigh, Cheshire, and Derbyshire, for fragments of the 
 Tilestones which occur at the base of the Cornstone group 
 have been found in the basal Carboniferous sandstone of 
 Flint. Eastward, or rather north-eastward, it probably 
 did not extend far, for if (as we suppose) there was land 
 in that direction during Silurian times, the area of this 
 land is likely to have been much larger during the time 
 of the Lower Old Eed, which was one of upheaval. South- 
 eastward, near Berkeley in Gloucestershire, it is either 
 absent or very thin, but southward there are probably 
 large tracts of rock which were continuous with the Corn- 
 stone series, though these are concealed beneath the 
 Devonian and Carboniferous rocks. In Cornwall, however, 
 the Lower Devonians extend downward into a series of 
 grits and slates estimated to be 10,000 feet thick, and 
 these may be older than any in North Devon. 
 
 In Scotland there are four distinct areas of Old Red 
 Sandstone: (1) in Berwickshire and the Cheviot Hills; 
 
 (2) below and on either side of the great central coalfields ; 
 
 (3) in the north-east, over the Orkneys, Caithness, and 
 parts of Sutherland and Ross ; (4) a small area in 
 Argyle shire. In all these there is the same general suc- 
 cession, viz., a great series of red and purple conglomerates 
 and sandstones, with dark grey flags and shales, and inter- 
 bedded sheets of felsite and porphyrite. These beds in 
 every case either pass down into Silurian rocks (as in the 
 Pentland Hills), or rest unconformably upon rocks that 
 are older than the Silurian. Above them there is always 
 
52 PALEOZOIC TIME. [CHAP. V, 
 
 an unconformity, and they are succeeded by other red 
 sandstones and conglomerates which have been termed the 
 Upper Old Red. Neither series contains any marine fossils,, 
 but fish have been found abundantly in both. 
 
 The Old Bed Sandstone of Scotland has excited the 
 admiration and kindled the enthusiasm of many Scotch 
 geologists. Its immense thickness, the varied colours of 
 its component strata, its peculiar scenery, and the extra- 
 ordinary forms of its entombed fossils, have furnished 
 themes for all who have studied this unique formation. 
 Immortalized by the pen of Hugh Miller, the wonders of 
 the Old Eed Sandstone are familiar to all, while its history 
 in connection with the scenery of Scotland has been 
 recorded in the graphic and artistic descriptions of Archi- 
 bald G-eikie. 
 
 Both writers have been struck by its massive thickness,, 
 and by the proofs of its having once extended far beyond 
 its present limits over the gneissic districts of Scotland. 
 Miller thought that it must originally have covered the 
 whole Highland region " from Ben Loinond to the Maiden- 
 paps of Caithness ; " 1 and though Dr. Geikie does not 
 accept this view, and believes that the areas in which it 
 occurs were always distinct and separate, yet he is forced 
 to admit that the Highland tracts which were not so 
 covered must have been comparatively small. Thus, after 
 describing the vast natural pyramids of Morven and the 
 Maidenpap, which form such conspicuous landmarks in 
 Caithness, and the chain of rounded, craggy, conical hills 
 between G-olspie and Helmsdale, he says 2 : "It is impos- 
 sible to look at these brown hills without being convinced 
 that they remain as a mere fragment of a great sheet of 
 conglomerate and sandstone which stretched away west- 
 ward across the abraded platform of schists forming the 
 
 1 " The Old Red Sandstone," second edition, p. 53. 
 
 2 " Scenery of Scotland," second edition, p. 139 et seq. 
 
HAP. V.] DEVONIAN PERIOD. 53 
 
 interior of Sutherland. But as if to make this point quite 
 certain, in the very heart of the county, the two solitary 
 conical mountains of Ben G-riam, 1,936 feet, which rise so 
 conspicuously above the worn platform of old crystalline 
 rocks, are cakes of conglomerate formed out of the detritus 
 of the schists on which they lie. . . . The same deposit 
 {i.e. Old Red conglomerate) runs southward from Suther- 
 land along the eastern coast of Ross and the shores of the 
 Moray Firth. It stretches up the valley of the Great Glen 
 and rises in Mealfourvonie to a height of 2,284 feet. 
 Thence it sweeps eastward along the seaboard of the coun- 
 ties of Inverness, Nairn, Elgin, Banff, and Aberdeen, and 
 detached portions are found thirty or forty miles in the 
 interior. . . . The highest of them is that which runs up 
 the valley of the River Avon above Toinintoul, where it 
 reaches a height of upwards of 1,300 feet above the sea. 
 The coarseness of the conglomerate at this locality is re- 
 markable ; huge blocks of the schists and other crystal- 
 line rocks of the district piled up in the conglomerate 
 there, bear emphatic witness to the abrasion of the High- 
 lands during, as well as before, the time of the Old Red 
 Sandstone." 
 
 "Along the southern border of the Highlands the evi- 
 dence is less obtrusive, but perhaps no less definite. 
 From sea to sea the Highland mountains are there flanked 
 by the Old Red Sandstone in low rolling plains that creep 
 up to the base of the hills, but sometimes, as in the case 
 of the Braes of Doune, rising into long heathery heights, 
 that form a kind of outer rampart to the main mass of 
 the Highlands. Even from a distance the stratification of 
 the conglomerates and sandstones of these uplands can be 
 easily traced, the beds presenting their denuded truncated 
 -ends toward the mountains, to which they evidently at one 
 time were prolonged, and from, the waste of which they 
 were formed. If we prolong with the eye the lines of 
 
54 PALEOZOIC TIME. [CHAP. V 
 
 these truncated strata, we see that they probably once- 
 stretched far away into the interior of the Highlands." 
 
 On the south side of the central Lowland tract the belt 
 of Lower Old Red is partly overlapped by the Upper divi- 
 sion, but from Girvan to the Pentland Hills it is faulted 
 against the older rocks, and there can be no doubt that 
 its original limit lay far to the south of its present 
 boundary. 
 
 In the north of Ireland there are two areas which exhibit 
 a set of rocks which are similar to the Lower Old Red of 
 Scotland, one of these is a tract about thirty miles long 
 by ten wide, lying between Lough Erne and Pomeroy in 
 Tyrone ; the other is a very small tract on the north coast 
 of Donegal. 
 
 In the south of Ireland there is some uncertainty about 
 the stratigraphical relations of the rocks which lie between 
 the Silurian and the Carboniferous systems. Such rocks 
 are only found in Kerry and Cork, and are known as the 
 Glengariff Grits ; they consist of hard green and purple 
 sandstones, with purple slates and some beds of conglome- 
 rate. In the Dingle promontory these beds conformably 
 succeed the Silurian, and are covered unconformably by 
 the conglomerates of the (so-called) Upper Old Red Sand- 
 stone. Further south, however, near Killarney, the upper 
 conglomerates are absent ; the highest Glengariff slates are 
 succeeded by the sandstones of the Lower Carboniferous 
 series. At Glengariff the Carboniferous slate has grey 
 grits and slates at its base (Coomhola grits), which seem 
 to rest conformably on the Glengariff slate and grit series. 
 Still further south, near Toe Head, the yellow sandstones 
 again come in between the Glengariff and the Carboniferous- 
 slates. 
 
 Professor Hull believes that the Carboniferous conglo- 
 merates are overlapped southward by higher beds, and that, 
 these come to rest upon the Glengariff grits at Killarney 
 
CHAP. V.] DEVONIAN PERIOD. 55 
 
 and Kenmare ; lie thinks the apparent conformity is decep- 
 tive, and that there is everywhere a great break between 
 the GlengarifE series and the Carboniferous beds. It is 
 certainly very difficult to reconcile the Dingle and G-len- 
 gariff sections on any other view, for there is no reason to 
 believe that there are any beds at Grlengariff which are un- 
 represented at Dingle, but rather that there are beds below 
 the Carboniferous shale east of Dingle which are absent in 
 the Glengariff country, so that, as Professor Hull argues, 
 the greater break is actually where there is least actual 
 evidence of it. The G-lengariff grits occupy a large surface 
 area in the south of Kerry, and extend eastward through 
 the central part of Cork. They are believed to underlie 
 the whole of South Cork and the greater part of Kerry, 
 but their northern limit is unknown, and is probably con- 
 cealed under the Carboniferous beds of North Cork and 
 Limerick. 
 
 2. Devonian System. The rocks of this system are only 
 found in the south of England, and they are only exposed 
 to view in the counties of Somerset, Devon, and Cornwall. 
 
 The rocks of North Devon and Somerset are divided into 
 three groups, which, as at present defined, consist respec- 
 tively of the following strata : (1) hard purple and grey 
 grits at the base, with grey slates and thin grits above; 
 (2) sandstones succeeded by a series of thin-bedded lime- 
 stones, grits, and slates above these are thick green and 
 grey slates ; (3) purple slates succeeded by red, brown, and 
 grey sandstones. 
 
 In South Devon and Cornwall the rocks are so contorted 
 and faulted that it is difficult to determine the real se- 
 quence, but it is known that there are (1) red sandstones 
 and slates with Lower Devonian fossils, (2) a great series 
 of slates and limestones (with interbedded volcanic rocks), 
 which represent the Middle Devonian, and (3) a slate and 
 sandstone r group resembling that in North Devon. 
 
56 PALAEOZOIC TIME. [CHAP. V. 
 
 In North Devon no base is seen ; in Cornwall there are 
 beds which may be older than any in North Devon, but 
 it is not known whether they rest on rocks of Silurian age, 
 or lie unconformably on the Ordovicians of Mevagissey. 
 
 In comparing the rock- series of North and South Devon, 
 we may notice the prevalence of sandstones in the northern 
 area, especially in the lower half of the system, showing 
 the neighbourhood of land ; the same conclusion may be 
 drawn from a comparison of the limestones, which are 
 much thicker and more fossiliferous in South Devon, indi- 
 cating a greater depth of water in that direction. 
 
 As regards the original extension of these Devonian 
 rocks there can be little doubt that it was chiefly in an 
 easterly direction, and that the sea in which the Middle 
 Devonians were formed shallowed toward the west and 
 south. Rocks belonging to the Middle Devonian have been 
 found in deep borings below London, and at Turnford in 
 Essex ; they occur also in Belgium and the north-east of 
 Trance, so that it is highly probable that they were con- 
 tinuous over the whole area now occupied by the English 
 Channel and the southern counties of England. In Nor- 
 mandy there is an absence of Middle and Upper Devonian, 
 though there are thick deposits of Lower Devonian age. 
 
 3. Upper Old Red Sandstone. The precise relations of 
 the strata which have been grouped as Old Red Sandstone 
 in Brecon, Hereford, and Salop remains to be ascertained. 
 Above the Cornstone group there are signs of unconfor- 
 mity according to the Rev. W. S. Symonds, and the suc- 
 ceeding beds are brown sandstones with red marls and 
 shales. These are sometimes called Middle Old Red Sand- 
 stone, and it is possible that they represent some of the 
 marine Devonian beds ; they are probably from 3,000 to 
 4,000 feet thick, and are certainly older and distinct from 
 the true Upper Old Red Sandstone of South Wales and 
 Ireland. 
 
CHAP. V.] DEVONIAN PERIOD. 57 
 
 The Upper Old Eed Sandstone proper borders the Car- 
 boniferous areas of Gloucester, Monmouth, and Glamorgan, 
 and stretches westward into Carmarthen and Pembroke, 
 overlapping both the underlying groups and the Silurian 
 rocks, till it rests directly on the Ordovician between Car- 
 marthen and Narberth. The beds consist of red and white 
 conglomerates at the base, succeeded by red marls, above 
 which are red and yellow sandstones with fish and plant 
 remains. It has been supposed that these strata are of 
 lacustrine origin, but no freshwater mollusca have yet 
 been found in them, while Serpulce and the Pteropod Conu- 
 laria are said to occur in them, so that there seems much 
 more reason to regard them as marine. Southward they 
 are found in the Mendip Hills, and they were doubtless 
 continuous with the Pickwell Down Sandstones of North 
 Devon and the Cockington Beds of South Devon. To the 
 northward they are found in the Clee Hills of Shropshire, 
 but as they do not recur beneath the Carboniferous rocks 
 of the neighbouring coalfields, that seems to have been 
 nearly the limit of their original northward extension. 
 
 They may be represented in Anglesey, where there are 
 600 feet of red sandstone and conglomerate below the 
 Carboniferous Limestone, but neither here nor in Denbigh 
 and Flint is there any definite band of shale between the 
 sandstones and the limestones, so that it seems more pro- 
 bable that the former are shore beds of the age of the 
 limestone, and therefore newer than the true Upper Old 
 Eed Sandstone. 
 
 The same is the case in the north of England and in 
 the south of Scotland, where there is always a group of red 
 sandstones at the base of the Carboniferous system, and in 
 Scotland these are sometimes 2,000 feet thick, but they 
 occasionally contain beds of red limestone with Carboni- 
 ferous fossils. 
 
 In the east of Scotland, however, there are older beds 
 
58 PALEOZOIC TIME. [CHAP. V. 
 
 which may be more truly called Upper Old Eed, since they 
 contain fish-remains of the Old Bed Sandstone type, and 
 they resemble the upper sandstones of Wales and Ireland. 
 In Fife and Forfar these consist of red conglomerates and 
 sandstones, surmounted by yellow sandstones and shales, 
 which are sometimes called the Dura Den beds, from a 
 locality near Cupar, whence many fine specimens of fish 
 have been obtained. Similar sandstones occur in Elgin on 
 the Moray Firth. 
 
 In Ireland the Upper Old Eed Sandstone is confined to 
 the southern part of the country. It sets in below the 
 Carboniferous limestone and shale of Kilkenny and Water- 
 ford. Where best developed it is 3,200 feet thick, and 
 consists of a basement conglomerate overlain by red and 
 purple sandstones and red shales, above which are yellow 
 and greenish sandstones with olive green shales. These 
 last are known as the Kiltorcan Beds, and they contain the 
 freshwater mollusc Anodon Jukesii, together with numerous 
 plants, fish, and large Crustacea, and the beds are believed 
 to be lacustrine. 
 
 Beds of the same age and of similar aspect are seen at 
 various localities in Tipperary, Limerick, Cork, and Kerry, 
 so that they are believed to underlie nearly the whole of 
 the south of Ireland, but they are absent over certain tracts 
 in the west of Kerry, as mentioned on a previous page 
 (p. 54). In the Dingle promontory there are thick red con- 
 glomerates, estimated to be more than 2,000 feet, succeeded 
 toward Tralee by 1,500 feet of the Yellow Sandstone group ; 
 in Clare and Limerick they are very much thinner, and 
 they are believed to die out along a line drawn from 
 Galway Bay to Queen's County, and thence southward 
 through Kilkenny. 
 
CHAP. V.] DEVONIAN PEEIOD. 59 
 
 2. Geographical Restoration. 
 
 During this period great geographical changes took 
 place ; the greater part of Britain was elevated into dry 
 land, and formed part of a continent which must have had 
 a considerable extention to the north and west of our 
 islands. The sea which covered so large a part of the 
 British area in Silurian times was now contracted into a 
 much smaller space, and only lay over the southern part of 
 England, whence it stretched eastward through the north of 
 France and Belgium. Westward it seems to have extended 
 into Ireland (if the Glengariff grits are marine beds), but 
 can only have covered a comparatively small area in the 
 extreme south-western part of the country. 
 
 An arm of the sea is represented on the map (PI. II.) as 
 covering the area occupied by the Old Eed Sandstone of 
 Wales and Shropshire, for Professor Hull's opinion that 
 this was formed in a bay or estuary which opened out of 
 the Devonian sea seems more probable than the view 
 advocated by Sir A. Ramsay and Dr. Geikie, who regard it 
 as a purely lacustrine deposit. 
 
 Sir A. Ramsay points to the prevalent red colour of the 
 rocks, but red rocks can be formed in seas as well as 
 lakes. The organic remains are few ; there are fish and 
 large Crustacea, such as occur in the Scottish Old Red 
 Sandstone, but these may have been able to exist both in 
 salt and fresh water, like many fish at the present day. 
 The marine shell Lingida cornea, is said to occur in some 
 of the Cornstone beds, and this would certainly prove the 
 beds containing it to have been formed in salt water. 
 Lastly, we may observe that there is no physical evidence 
 to support the supposition of a land barrier to the south. 
 
 At the same time it is true that the Cornstone and Tile- 
 stone series hardly present the usual characteristics of an 
 estuarine deposit, and the inlet may have been a long bay 
 
60 PALEOZOIC TIME. [CHAP. V. 
 
 rather than an estuary. The nature of the deposits would 
 depend entirely on the character of the rocks which form 
 the neighbouring land, and it is evident that this land 
 must have consisted largely of granitoid, felspathic, and 
 quartziferous rocks, and though some of the material 
 doubtless came from the western side, yet it seems pro- 
 bable that the larger proportion came from the eastern. 
 We have seen that land-tracts formed in part of such rocks 
 lay over central England in Silurian times, and the 
 Devonian upheaval doubtless greatly extended their boun- 
 daries, especially toward the east and the north. 
 
 We have no evidence as to the direction of the inlet 
 further northward, but it probably narrowed, and may 
 have received the waters of a river that drained the land to 
 the north and east. In the north-west of England and in 
 the Isle of Man there is a great unconformity between the 
 older Palaeozoic rocks and the Carboniferous, so that it is 
 inferred that all the north of England was land. 
 
 Parts of Scotland were also dry land, and the earth- 
 movements in this region seem to have resulted in the for- 
 mation of several mountain ranges having a north-east and 
 south-west direction, between which ranges were low-lying 
 tracts that were at first inlets of the sea, but by the con- 
 tinued elevation of the land were apparently converted into 
 large inland lakes. 
 
 Dr. Arch. G-eikie considers that the four areas of Old 
 Bed Sandstone, mentioned on p. 51, were distinct and 
 separate basins of deposit, at any rate during the earlier 
 half of the period ; l that they were also disconnected from 
 the sea, and formed large inland lakes. He has, therefore, 
 
 1 The great thickness of material in them would be more easily under- 
 stood if they lay between lofty mountain ranges, for they find a parallel 
 in the Siwalik group of India, and the manner of their formation is illus- 
 trated by deposits in the upper basin of the Indus. See Drew in 
 " Quart. Journ. Geol. Soc.," vol. xxix. p. 441. 
 
PLATE III. SUPPOSED GEOGRAPHY OF LOWER DEVONIAN AND LOWER 
 OLD RED SANDSTONE TIME. 
 
CHAP. V.] DEVONIAN PERIOD. 61 
 
 proposed separate names for these basins, calling the 
 south-eastern area Lake Cheviot, the central one Lake 
 Caledonia, the small western basin Lake of Lome, and the 
 northern basin Lake Orcadie. 
 
 From the proofs which have been adduced of the origi- 
 nal wide extension of the Old Red Sandstone (p. 52), it 
 might be thought that the three principal basins could 
 hardly have been separate lakes, but must have been inlets 
 proceeding from one large inland sea, the greater part of 
 which lay to the east of Scotland ; and, indeed, so far as- 
 the stratigraphical evidence goes this would be the most 
 natural conclusion, for the lithological differences between 
 the strata of the several basins are hardly greater than the 
 differences which exist between the Lanark and Forfar 
 types in the same Caledonian basin. The palaeontological 
 differences are, however, very much greater, the piscine 
 fauna of the Forfar and Caithness flags being so distinct 
 that Sir R. Murchison thought they could not be of the 
 same age, and was led to suggest that the Caithness flags 
 formed a middle group distinct from the Lower Old Red, 
 and of younger date than the flags of Arbroath in Forfar. 
 Dr. Geikie has shown that this is improbable, and that the 
 discrepancy is not complete, and that the general succes- 
 sion of beds in the two areas is very similar. " The 
 admitted palaeontological distinctions are probably not 
 greater than the striking lithological differences between 
 the strata of the two regions would account for, or than 
 the contrast between the ichthyic faunas of contiguous 
 water-basins at the present time." l The difference is, 
 however, sufficiently remarkable, for out of eighteen genera, 
 with sixty species from Caithness, and ten genera with 
 seventeen species from Arbroath, only four genera and one 
 or two species are common to the two areas. So great a 
 difference, though it may perhaps be lessened by future 
 1 " Textbook of Geology," first edition, p. 715. 
 
62 PALAEOZOIC TIME. [CHAP. V. 
 
 discoveries in Forfar, affords good ground for concluding 
 that there was no direct communication between the waters 
 of the two lakes. 
 
 There is less evidence for regarding the Cheviot basin as 
 distinct from the Caledonian, as no fish have yet been 
 found in the Cheviot district, and we do not know how far 
 the Lower Old Red originally stretched over the southern 
 uplands ; much of it was removed before and during the 
 formation of the Upper Old Red, the latter in all proba- 
 bility deriving much of its material from the destruction 
 of the older series. The Lower Old Red partakes in the 
 plication of the Silurian and Ordovician rocks of southern 
 Scotland, and it may for ought we know have been co- 
 extensive with them over the whole region. On the other 
 hand, it should be noted that the Lower Old Red of the 
 Cheviot district rests unconformably on the Silurian, 
 which is an unusual relation, and suggests that the 
 Cheviot basin was formed at a somewhat later date than 
 the Caledonian basin by a local depression of the land 
 surface. This, however, is not incompatible with its 
 having then been an inlet or extension of the Caledonian 
 Lake, but I have not ventured to express this view on 
 the map, which is a rendering of Dr. G-eikie's opinion. 
 
 The greater part of Ireland likewise seems to have been 
 land enclosing lake basins, and was doubtless at this time 
 connected with England and Scotland, so that the whole 
 formed one mass of land, and was part of a large con- 
 tinent that extended far westward into the place now 
 occupied by the North Atlantic. The tract of Old Red Sand- 
 stone in Tyrone being in alignment with that of the central 
 Scottish basin, Professor Hull has suggested that the Lake 
 Caledonia extended thus far into Ireland, and I have 
 adopted this view in the restoration of Old Red Sandstone 
 geography (PI. III.). The other small tract of Old Red 
 recently discovered in Donegal may have been formed in a 
 
CHAP. V.] DEVONIAN PERIOD. 63 
 
 separate basin, which has been named Lake Fanad by 
 Professor Hull. 
 
 We may now glance at the succession of events in the 
 south of England. Here, in the sea which occupied the space 
 between the northern part of France and the Bristol 
 channel, there had been continuous deposition of sediment 
 throughout the Devonian period. After the first elevation 
 at the close of Silurian times, this southern area does not 
 seem to have been affected by the upheaval which was in pro- 
 gress to the northward, and indeed it may have occupied a 
 trough of compensating depression. The western part of it 
 was raised into land, however, after the formation of the 
 Glengariff Grits, all the south of Ireland probably being 
 land during the formation of the Middle Devonian rocks. 
 
 According to Professor G-osselet, the Devonians of the 
 Boulonnais and the Ardennes were deposited in a narrow 
 strait connecting the wider seas of the Westphalian and 
 the Anglo-French areas. 1 Along the northern side of the 
 Devonian tract from Boulogne to Namur the Lower Devo- 
 nian is absent, and the base of the Eif elien division consists 
 of conglomerate and sandstone. It is highly probable that 
 the land thus indicated was connected with that which lay 
 over the centre and east of England. 
 
 Parts of Brittany and Normandy seem also to have been 
 land, and Professor de Lapparent thinks that they formed 
 an island, the limits of which were very nearly the same as 
 those of the present massif of Cambrian and Ordovician 
 rocks. Inlets of the Lower Devonian sea penetrated the 
 district near Brest, in Basse Loire, on the frontiers of 
 Maine and from the Normandy side ; but whether it sank 
 beneath the sea of the Middle and Upper Devonian epochs 
 is not known, as the strata of these stages occur only to 
 the south in Basse Loire! 
 
 1 " Esquisse geologique da nord de la France," p. 60; but the evidence 
 for the southern shore of this strait is inconclusive. 
 
64 PALEOZOIC TIME. [CHAP. V. 
 
 In the tracts which were covered by the sea there was 
 continuous deposition throughout the period, but in the 
 lacustrine areas it appears to have ceased altogether for a 
 time ; there is a great gap between the Lower and Upper 
 Old Eed Sandstone, and we have no records of the inter- 
 vening time. But this very absence of deposits is in itself 
 evidence of the conditions which prevailed the lakes must 
 have been dried up and converted into land surfaces, pro- 
 bably in consequence of the continued elevation of the 
 country, and the deepening of the river channels which 
 would result from this elevation. 
 
 We may, therefore, conclude that the general succession 
 of events in the northern areas was as follows : at the 
 beginning of the period the upheaval of the ridges which 
 subsequently became mountain ranges contracted the sea- 
 space into gulfs, which were gradually shallowed by the 
 material poured into them from the land on either side, 
 and by the continued upheaval of the country, till they 
 were entirely isolated from the sea, and were converted 
 into large freshwater lakes, comparable to those of modern 
 North America, and tenanted by a great variety of curious 
 fish. Lake Caledonia must, indeed, have greatly resembled 
 Lake Michigan, which has a length of 345 miles, and an 
 extreme width of only 84 miles. Now the Scottish portion 
 of Lake Caledonia has a length of 160 miles ; and if, as 
 Professor Hull supposes, it stretched continuously into 
 North Ireland, we must add another 80 miles to its western 
 extension, giving a total of 240 miles, while how far it ex- 
 tended to the east of Scotland we have no means of know- 
 ing, but it may well have been 300 miles in length, and 
 its extreme width was perhaps not more than 80 or 90 
 miles. The greater part of Lake Orcadie lay outside the 
 present limits of Scotland, and in that part of the continent 
 which stretched toward Scandinavia, so that we can form 
 no idea of its size. The other lakes seem to have been 
 
CHAP. V.] DEVONIAN PERIOD. 65 
 
 small in comparison, though Lake Cheviot may have been 
 40 or 50 miles long. 
 
 During the existence of these lakes volcanic activity was 
 rife, and immense sheets of lava were poured over the 
 country and interbedded with the lacustrine deposits, and 
 all this time it is probable that the lake bottoms were not 
 very far above the sea. 
 
 Along the southern border of the central basin there is, 
 in fact, evidence that there must have been some alter- 
 nating movements of depression, or such differential move- 
 ments between the lake-basin and the dividing ridges of 
 land that the area of the former was sometimes invaded 
 by the sea. Thus, near Lesmahago, a few hundred feet 
 above the base of the red beds, there are shales containing 
 marine fossils of Silurian species, and again, near Car- 
 michael in Lanark, 5,000 feet above the base, there is a 
 band of shale which has yielded a Graptolite, an Orthoceras, 
 and a Beyrichia f orms which must have continued to exist 
 in the neighbouring sea, and which prove that the Silurian 
 fauna was still prevalent in that sea. This shale band, 
 intercalated between thick masses of red sandstones, shales, 
 and conglomerates, which are supposed to be of lacustrine 
 origin, is a proof that the lake-basins were at first isolated 
 from the sea by the ridging up of land-barriers, rather than 
 by any general elevation of the country. 
 
 During the formation of the higher beds, however, we 
 may suppose that a general elevation took place, and that 
 the lakes came to have excurrent as well as incurrent 
 rivers, till in course of time, as the excurrent streams cut 
 their channels deeper and deeper, the waters of the lakes 
 were partially or completely drained off, just as the great 
 Tertiary lakes of North America were drained by the ex- 
 cavation of the Colorado canon. The country would then 
 present the aspect of a high and dry upland, formed of 
 lofty hill ranges separated by immense sandy plains, the 
 
66 PALEOZOIC TIME. [CHAP. V. 
 
 sites of the desiccated lakes ; through these plains ran the 
 rivers in deep and narrow channels, while on the mountain 
 slopes piles of debris were prepared by the agencies of dis- 
 integration and detrition. It is, indeed, not unlikely that 
 much of the material forming the conglomerates of the 
 Lower Carboniferous series was originally prepared by sub- 
 aerial agencies, and was only rearranged by the waters of 
 the later epoch. 
 
 A reverse movement at length set in toward the end of 
 what must be called the Devonian period ; portions of the 
 old lake-basins were again filled with water, the area of 
 which widened and deepened as the land sank ; torrents 
 washed in the detritus of the land, and the material thus 
 collected became the conglomerates and sandstones of the 
 Upper Old Red and Lower Carboniferous series. 
 
 This depression led to the formation of a large lacus- 
 trine area in the south-west of Ireland, spreading over 
 the tracts now known as the counties of Clare, Limerick, 
 Kerry, Cork, Waterford, Tipperary, and Kilkenny. Its 
 northern shore appears to have been somewhere along the 
 parallel of Galway Bay ; the Granitic and Ordovician rocks 
 of Wicklow, Carlow, and Wexf ord formed its eastern boun- 
 dary, while how far it extended to the south and west we 
 have no means of knowing, except that in the Dingle and 
 Kenmare districts we appear to be approaching its western 
 shores. From Dingle to Thomastown in Kilkenny is a 
 distance of 135 miles, and from G-alway Bay to the Old 
 Head of Kinsale is 108 miles; this would form a fine 
 sheet of water, but even if it stretched another 100 miles 
 to the southward, it would only have been about half the 
 size of the modern Lake Superior. 
 
 In this lake were laid down the strata described on p. 
 58, and at the epoch of the Kiltorcan beds, with their 
 abundant remains of plants, it is evident that its shores 
 were bordered by tracts of fertile land, on which grew the 
 
CHAP. V.] DEVONIAN PERIOD. 67 
 
 Lepidodendra, Cyclostigmce, and the splendid ferns known 
 as Palceopteris hibemica, the fronds of which are nearly two 
 feet in breadth. Eventually here and elsewhere the con- 
 tinued depression of the land brought the level of the lake 
 waters down to that of the Carboniferous sea, which was 
 gradually extending itself over the lower parts of the great 
 Devonian continent. 
 
 This view of the relations of the so-called Upper Old 
 Red to the Carboniferous system has been well expressed 
 by Mr. B. N. Peach. 1 " As the land in the northern areas 
 gradually sank, the lacustrine and littoral deposits were 
 succeeded conformably by estuarine and marine strata of 
 Lower Carboniferous age, and a much newer facies of fish 
 fauna followed the Old Eed types. . . . This remarkable 
 palaeontological break in a conformable series of strata can 
 be satisfactorily explained if we regard the Upper Old Eed 
 fishes as the survivors of an older fauna still confined to 
 land-locked basins, while the Carboniferous forms suddenly 
 gained access to the Scottish area from the open sea, where 
 they had developed at a much more rapid rate than their 
 less favoured relatives." 
 
 Whether the Welsh gulf continued open throughout the 
 whole period we are not at present in a position to say ; 
 possibly it was at times completely silted up and converted 
 into a low-lying tract of land, but it was under water again 
 during the formation of the Upper Old Red Sandstone, and 
 its limits were then greatly extended in an east and west 
 direction. The sea then probably stretched westward for 
 some distance toward Ireland, and was only separated by 
 narrow barriers from the lacustrine waters of that area. 
 When at length these barriers were submerged, and the 
 sea spread over all the lower parts of the great Devonian 
 continent, it ushered in a new fauna, and with this we com- 
 
 1 "Proc. Roy. Phys. Soc. of Edinburgh," vol. ix. p. 13. 
 
68 PALAEOZOIC TIME. [CHAP. V. 
 
 mence a new period of geological time. The history of this 
 depression belongs to the next chapter, but it has this con- 
 nection with the geography of Devonian times, that the 
 relative height of different portions of the Devonian con- 
 tinent may be indicated by the relative age of the Carboni- 
 ferous beds which lie upon them. 
 
CHAPTEE VI. 
 
 CARBONIFEROUS PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 ^ABBOSTIFEROUS rocks occupy large areas in the 
 \_/ British Isles and they are known to have a wide sub- 
 terranean extension (see " Historical Geology," p. 181). 
 They exhibit three principal facies, which may be called 
 (1) the southern or Culm -measure type, (2) the central or 
 Pennine type, (3) the northern or Scottish type. 
 
 The southern type is found in Devonshire and in the 
 south-west of Ireland ; it consists mainly of black and grey 
 shales (cleaved into slates in Ireland), the limestones being 
 very thin and insignificant. The lower part consists of 
 green and grey shales with bands of sandstone (Baggy and 
 Pilton Beds), the middle of black shales and thin lime- 
 stones (Lower Culm-measures), the upper of hard grey 
 grits with bands of shale (Middle and Upper Culm- 
 measures). 
 
 The central type is more varied and consists of a series 
 which is divisible into four groups as follow : 
 
 4. The Coal-measures (shales, sandstones, and coals). 
 
 3. The Millstone Grit (sandstones and shales). 
 
 2. The Upper or Toredale Limestones and shales. 
 
 1. The Lower Limestones, with shale and sandstone at 
 the base. 
 
 Nos. 1 and 2 are known as the Lower Carboniferous 
 series, and sometimes attain a thickness of 8,000 feet. 
 
70 PALEOZOIC TIME. [CHAP. VI. 
 
 Nos. 3 and 4 are the Upper Carboniferous series, and are 
 as much as 12,000 feet thick in some parts of Lancashire 
 and Yorkshire. This type prevails over the larger part of 
 England and Ireland. 
 
 The northern type is differently divided in Northumber- 
 land and Scotland, but the following classification would 
 apply to both areas : 
 
 JT ( The Coal-measures (2,000 to 3,000 feet). 
 
 ' I The Millstone Grit (100 to 600 feet). 
 
 A limestone group with shales and coals (1,500 
 
 to 3,000). 
 Lower. ^ A carbonaceous shale group (800 to 2,500). 
 
 A sandstone group with basal conglomerates 
 (1,000 to 3,000 feet). 
 
 Certain areas in the north of Ireland exhibit beds of a 
 similar type. 
 
 The records of the Carboniferous period being thus more 
 complete than those of earlier times, and the rocks being 
 more fully exposed and more easily classified, we possess 
 more certain grounds on which to reconstruct the geography 
 of the British area, at any rate during the early stages of 
 the period. 
 
 It is clear that the period was ushered in by the partial 
 submergence of the great continent which included so large 
 a part of Britain in the preceding (Devonian) period. The 
 movement of depression seems to have been very different 
 from the movement which raised that continent ; the up- 
 heaval was effected by a force which acted rather horizon- 
 tally than vertically, forcing up the earth's crust by lateral 
 compression into a series of mighty ridges and furrows. 
 The Carboniferous submergence was apparently an even 
 and uniform downward movement gradually bringing the 
 lower portions of the pre-existent land beneath the level 
 of the sea. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 71 
 
 The only district which presents evidence of differential 
 movement is that of the Old Red Sandstone tract of 
 Shropshire, for though the Upper Old Eed exists there, 
 the Lower Carboniferous beds are absent, and the several 
 stages of the Upper Carboniferous rest unconformably on 
 the Old Red Sandstone and Silurian rocks ; whence we 
 may infer that though this was low ground at the close of 
 Devonian time, it was not submerged beneath the Lower 
 Carboniferous sea, but was undergoing elevation which 
 kept it above water till late in the Carboniferous period. 
 
 In dealing with the evidence derivable from, the litho- 
 logical changes in the Lower Carboniferous rocks, I propose 
 to follow a different method from that adopted in previous 
 chapters. Although there can be no doubt that the greater 
 part of England and Ireland was submerged during the 
 formation of the Carboniferous Limestone, I think there are 
 grounds for believing that a large island of irregular shape 
 existed over the area now covered by St. George's Channel, 
 and that it stretched northward into Scotland, and eastward 
 through the centre of Wales and the midland counties of 
 England. Instead therefore of discussing the conclusions 
 to be deduced from a study of the English, Scotch, and 
 Irish rocks respectively, I propose to adopt a more syn- 
 thetic method, and, taking the existence of this island as a 
 theorem, to state the facts which may be regarded as 
 strong evidence, even if they do not amount to proof of the 
 proposition. 
 
 It will be convenient to start with Shropshire, as the 
 evidence for the existence of land in that county has just 
 been alluded to ; it is corroborated by the rapid northerly 
 thinning of the Carboniferous Limestone series in Gloucester 
 and Honmouth ; near Bristol this series has a total thick- 
 ness of about 2,600 feet, including the lower and upper 
 shales ; near Chepstow it is about 1,500 feet thick, and in 
 the Forest of Dean it is only 840 feet, having lost 1,760 feet 
 
72 PALEOZOIC TIME. [CHAP. VI. 
 
 in a distance of twenty to twenty-five miles ; if its attenuation 
 continued at the same rate it must have died out some ten 
 miles north of the Forest of Dean coalfield, i.e. a little to 
 the south of the 52nd parallel of latitude, and as a mat- 
 ter of fact it appears to be absent at Newent. The same 
 northerly thinning occurs throughout the South Wales 
 coal-basin, the Limestone series on its southern border 
 being variously stated as from 1,000 to 2,000 feet thick, 
 while along the northern border it is not more than 500 
 or 600 feet thick, and near Haverfordwest it appears to 
 die out altogether, and to be overlapped by the Coal- 
 measures. These facts may be taken as indicating the 
 existence of land a few miles north of the present boundary 
 of the limestone. 1 
 
 From Pembrokeshire we pass across to the coast of 
 Wexford in Ireland, and as we find very similar conditions 
 existing there, it is exceedingly probable that the coast-line 
 we are following was continuous from Pembroke to Wex- 
 ford. Carboniferous rocks occur round Wexford Harbour, 
 and extend south-westward in a narrow strip between 
 areas of Cambrian rocks, and are found again on either 
 side of the entrance to Waterford Harbour. Mr. Kinahan 
 states that the dark shales and limestones which are found 
 along the southern margin graduate into red shales, sand- 
 stones, and conglomerates along their northern margins, 
 and that " these rocks seem to have accumulated in a 
 narrow bay which shallowed out eastward." 2 
 
 That the Cambrian, Ordovician, and Granitic areas of 
 Wexford, Carlo w, and Wicklow were land at the time 
 
 1 That the thinning of the limestone was in the direction of land, and 
 not away from it, is shown by the simultaneous thinning of the Mill- 
 stone grit and the overlap of the Coal-measures. We know also that 
 the Carboniferous limestone was often formed in close proximity to 
 shore-lines. 
 
 8 " Geology of Ireland," G. H. Kinahan, p. 78. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 73 
 
 when the lower beds of the Carboniferous limestone were 
 formed is shown by the* overlap of this limestone on to the 
 granite of Carlow, and it is probable that this land being 
 steep and mountainous was not wholly submerged till the 
 close of the Carboniferous period, and perhaps not even 
 then. This lower limestone continues to border the older 
 rocks through Kildare, but in County Dublin it appears to 
 be overlapped by shales belonging to the Calp and Upper 
 Limestone series. 
 
 The limestones between Howth, Swords, and Rush are 
 believed to belong to the Lower Limestone, but they show 
 unmistakable evidence of the close neighbourhood of land. 
 The Hill of Howth was clearly an island in this Lower Lime- 
 stone sea, and part of a shore conglomerate still exists 
 there. Between Kush and Skerries the limestones include 
 thick beds of conglomerate containing pebbles derived 
 from the neighbouring Ordovician rocks ; there is some 
 doubt whether these limestones belong to the Lower or 
 Upper division, 1 but there is no doubt that farther north- 
 west, near the Naul, the Upper Limestone rests against the 
 Ordovician shore, and that it is moreover overlapped by the 
 succeeding (Yoredale) shale group. At one place there 
 are boulder beds, consisting of blocks from the Ordovician 
 rocks cemented together by grey Carboniferous Limestone, 
 and Professor Jukes observes : 2 " This is evidently a portion 
 of the very beach or margin of the Carboniferous sea in 
 which the fallen blocks and shingle from the wasting land 
 above were enveloped in the calcareous deposits of the 
 Carboniferous period." 
 
 The facts described in the memoir referred to seem ex- 
 plicable only on the supposition that the beds were deposited 
 in a bay which had land to the south, east, and north 
 
 1 See " Mem. Geol. Survey (Ireland), Expl. of Sheets 102 and 112," 
 pp. 65, 66. 
 
 2 Op. cit., pp. 59, 60. 
 
74 PALEOZOIC TIME. [CHAP. VI. 
 
 of it. The older beds are only found in the central part 
 of the area, and the water was n6t clear enough for the 
 formation of limestone during the whole time, the higher 
 beds being chiefly dark earthy shales, which overlap the 
 limestones on to the sinking land both northward and 
 southward, as doubtless they also did to the eastward. 
 The great development of shales in this district may have 
 been caused, as Jukes suggested, either by the influx of 
 a river which had previously some other debouchure, or 
 by the sea having reached some tracts of earthy Ordovician 
 shale which had previously been above its level (op. cit., 
 p. 23). 
 
 North of the area just described, and around the town 
 of Drogheda, is another tract of Lower Carboniferous strata 
 lying in a hollow between ridges of Ordovician rocks. The 
 Lower Limestone is only found to the westward, and dis- 
 appears about two miles east of Slane, owing " to the con- 
 formable overlap of the higher beds of the formation on to 
 the Silurian (i.e. Ordovician) rocks, over which they were 
 deposited along a gradually shelving shore." This tract 
 was probably, therefore, another bay narrowing eastward. 
 
 The tract of Carboniferous beds between Ardee and 
 Kingscourt exhibits a complete section of the Lower series, 
 and these beds doubtless extended originally all over the 
 Ordovician tracts of Cavan, Monaghan, and Louth. There 
 are also outlying tracts near Dundalk and Carlingford, but 
 these seem to belong to the Upper Limestone series, and it 
 is not unlikely that a large part of County Down was a 
 promontory of land jutting westward into the sea of the 
 Carboniferous Limestone. In the north-east of County 
 Down, at Holywood and Castle Espie, there are limestones 
 associated with red shales and sandstones, which are pro- 
 bably shore-beds of Upper Limestone age. 
 
 1 " Mem. Geol. Snrv. (Ireland), Expl. Sh. 91 and 92," p. 35. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 75 
 
 We have now traced indications of the existence of a 
 coast-line all the way from Wexf ord and Waterford to the 
 north of County Down, and here we are, doubtless, not far 
 from its northern limit, for there can be little doubt that 
 there was a connection between the Irish and Scotch waters 
 at this period. The rocks of County Down are evidently a 
 continuation of the Silurian and Ordovician tracts of 
 southern Scotland, and it is highly probable that in early 
 Carboniferous times they formed one continuous mass of 
 land, and it is not at all improbable that this land included 
 the northern part- of the Isle of Man. It is true that there 
 is carboniferous limestone at the southern end of the Isle 
 of Man, but there is no proof that it ever extended far to 
 the north, and the red sandstones and cornstones of Peel 
 may be shore-beds of the Limestone sea, like the red sand- 
 stones of Scotland. 
 
 That this was the case on the northern border of the 
 land area we are now considering is the decided opinion of 
 the Geological Surveyors of Lanarkshire. Describing the 
 basal conglomerates of this district, they say: "These con- 
 glomerates continue to fringe the Carboniferous area, while 
 the strata above pass quite away. Hence, in this con- 
 tinuous band of conglomerate, one portion is on the horizon 
 of a low part of the Calciferous Sandstone series, while 
 another portion is on the horizon of the Carboniferous 
 Limestone series. It thus brings before us evidence of 
 shore conditions during a protracted submergence of this 
 area in Lower Carboniferous times." 1 It must be remem- 
 bered, also, that what is here called the Calciferous Sand- 
 stone is now regarded as contemporaneous with the lower 
 part of the English Carboniferous Limestone. 
 
 Eeturning to the Isle of Man, the existence of the Lime- 
 stone series there is no proof that there was open sea to the 
 
 1 " Mem. Geol. Surv. of Scot., Expl. Sh. 15," p. 30. 
 
76 PALAEOZOIC TIME. [CHAP. VI. 
 
 westward. It is, of course, possible that there was com- 
 munication by way of a narrow strait between the Cariing- 
 ford area and that of the Isle of Man, but the evidence on 
 the Irish side is in favour of there having been a con- 
 tinuous mass of land over the western part of the Irish 
 Sea, and the Manx rocks are just as likely to have been 
 formed in a bay on the eastern side of this land, seeing that 
 there were several such bays on the western side. 
 
 Exactly the same reasoning applies to the Carboniferous 
 rocks of Anglesey. The succession here is very similar to 
 that of the Isle of Man a basal conglomerate, succeeded 
 by red sandstones and cornstones from 200 to 300 feet 
 thick, overlain by limestones only 450 feet thick, and 
 covered directly by the Millstone Grit. These small thick- 
 nesses suggest the neighbourhood of land, and that this 
 lay to the west is shown by the fact of the Limestone series 
 rapidly thickening to the east, and attaining some 2,000 
 feet in the north of Flint. It is quite possible, therefore, 
 that the western part of Anglesey was land, and that the 
 Carboniferous beds were deposited in a bay or inlet which 
 penetrated into this land, and narrowed south-westward. 
 
 Patches of limestone skirt the coasts of North Wales 
 and border the Silurian rocks along the Vale of Clwyd ; 
 here and in North Flint its thickness is about 1,500 feet, 
 and it keeps this thickness for some distance southward, 
 being still 1,200 feet thick at the north-west end of the 
 Eglwyseg escarpment near Llangollen, where it rests on 
 300 feet of yellow sandstone and conglomerate. Thence, 
 however, it thins very rapidly to the south-east, being only 
 600 feet thick at Trevor, and under 200 feet at Fron-y- 
 Cysyllte on the south side of the Dee ; thus, in a distance 
 of four miles, the red sandstones and about 1,000 feet of 
 the limestone have thinned out against a slope of Silurian 
 rock, a fact which suggests the existence of an island in 
 the sea of the Lower Limestone near Euabon and Chirk. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 77 
 
 Mr. Or. H. Morton 1 has shown that in this district the 
 Limestone is divisible into four stages, and that at Fron 
 only the highest, and 28 feet of the third remain. Near 
 Chirk the latter have thinned out, and only the uppermost 
 grey beds (137 feet thick) are found. That this thinning 
 indicates an island is proved by the white beds coming in 
 again below the grey at Craig Sychdin, seven miles south 
 of Fron, and these continue to form a base as far as 
 Crickheath Hill, when shales belonging to the second 
 stage appear, and at Llanymynech the total thickness of 
 the limestone has increased again to 450 feet. Here the 
 escarpment terminates ; and when Carboniferous strata 
 set in again five miles to the south-east, Coal-measures 
 rest on Silurian, so that the limestones had thinned out 
 in the interval. 
 
 With regard to the westerly extension of the Limestone 
 we are furnished with valuable testimony in the shape of 
 an outlier, faulted down against Silurian shales, near Cor- 
 wen, and no less than twelve miles W.S.W. of the Eglwyseg 
 escarpment. Moreover, the thickness here is still con- 
 siderable, probably about 750 feet, so that the limestone 
 must have extended some distance farther to the west and 
 south of Corwen. It is hardly likely, however, to have 
 reached so far as the Arenig mountains, though it may 
 have run up the valley of the Dee as far as Bala ; the 
 northern flank of the Berwyn mountains probably formed 
 its southern boundary, these mountains forming a pro- 
 montory which stretched north-eastward towards Llan- 
 gollen and Chirk, and separated what may be called the 
 Corwen bay from the Llanymynech bay (see map, fig. 2). 
 
 The absence of the limestone over the Shrewsbury dis- 
 trict indicates another extension of the land area between 
 Llanymynech and Wellington, where the border of the 
 
 1 " The Carboniferous Limestone and Cefn-y-Fedw Sandstone," 1879. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 79 
 
 limestone is again found. On the east side of the Wrekin 
 the basement beds consist of lava and volcanic ash, which 
 seem to have been the products of subaerial eruptions 
 from volcanoes situated on the border of the land ; on these 
 lies a thin representative of the Carboniferous Limestone 
 comprising 20 to 40 feet of limestone, overlain by about 
 the same thickness of shale and sandstone. The south end 
 of this outcrop is cut off by a fault, beyond which the 
 limestone is absent, and the Millstone Grit conglomerate 
 rests on the Silurian. It would appear, therefore, that the 
 greater part of Shropshire was land with open sea to the 
 north and north-west. 
 
 We have now returned to the county from which we 
 started, and the logical conclusion to be drawn from the 
 facts which have been described is that the whole area 
 inside the localities mentioned was a continuous mass of 
 land (see map, Plate IV.). 
 
 It only remains to give the evidence for the easterly ex- 
 tension of this land, and this was clearly given by Jukes 
 so long ago as 1853 in his " Memoir on the South Stafford- 
 shire Coalfield." He there describes the great uncon- 
 formity between the Coal-measures and the older rocks in 
 South Staffordshire and Warwickshire, these older rocks 
 being Silurian in the one case and Cambrian in the other. 
 The natural inference to be drawn from the facts cannot 
 be stated better than in Jukes' own words : "It is highly 
 probable that all this tract of country, together with much 
 of the adjacent district from Montgomeryshire to Leicester- 
 shire, became dry land after the close of the Silurian 
 period, rising perhaps very slowly, and undergoing a very 
 gradual and long- continued process of degradation as it 
 passed through the destructive plane of the sea-level ; 
 and that it remained above the waters during great part 
 of the period marked by the formation of the (Upper) 
 Old Bed Sandstone and Mountain Limestone, and that 
 
80 PALEOZOIC TIME. [CHAP. VI. 
 
 accordingly those two rocks were never deposited upon 
 it." l 
 
 On the north-east side of the Leicestershire coalfield the 
 Millstone Grit and Carboniferous Limestone are again 
 found ; and south-eastward, near Northampton, the Lime- 
 stone was found in one deep boring, and Lower Carboni- 
 ferous shales and sandstones in another ; but at Orton 
 (twelve miles to the north-east) a thin representative of the 
 Trias rests directly on a quartz-felsite resembling some of 
 the Charnwood rocks. 
 
 Whether the land we have traced terminated in Leicester- 
 shire, or widened out again eastward and formed part of 
 a larger land mass in that direction, there is at present no 
 evidence which will enable us to decide; but, as it 
 evidently became very narrow in Leicestershire, we have 
 thought it safer to show land on the map only so far as 
 there is evidence for it, and therefore to suppose that it 
 was surrounded by the sea in Lower Carboniferous times. 
 
 We have now to consider whether any other tracts are 
 likely to have existed as islands at this time, and the first 
 tract that claims attention is that known as the Lake Dis- 
 trict. That this was an island at the commencement of 
 the Limestone epoch is tolerably certain, as testified by the 
 conglomerates and sandstones which form the base of the 
 Limestone series ; but the question How long did it re- 
 main unsubmerged ? is a very difficult one to answer. " It 
 has been discussed by the Eev. J. C. Ward, 2 who comes to 
 the conclusion that only a very small area north of the 
 Keswick Valley could have been above water, since the 
 Mell Fell conglomerate runs up to a height of 1,760 feet. 
 Curiously enough, this conglomerate consists chiefly of 
 Upper Silurian detritus, and not of stones derived from 
 the Ordovician rocks against which it rests. Mr. Ward 
 
 1 " Geology of the South Staff. Coalfield," first edition, p. 253. 
 
 2 " Geol. Mag,," Dec. 2, vol. vi. (1879), p. 58. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 81 
 
 thinks it was formed in a narrow channel or strait which 
 separated a smaller northern island from a larger southern 
 one, and that the pebbles were drifted by a current from 
 the south, and accumulated chiefly at the eastern end of the 
 supposed channel, where their further northward progress 
 was impeded. 
 
 Mr. J. G-. GToodchild, however, informs me that he differs 
 from Mr. Ward's view, and believes the pebbles were 
 derived from northern sources. The Silurian rocks of 
 Westmoreland are strongly cleaved, and though a few of 
 the Mell Fell stones are undistinguished from Westmore- 
 land rocks, yet many pebbles of uncleaved mudstones 
 occur, together with other rock-fragments which are unlike 
 any in the Lake District, but can be matched with rocks in 
 the south of Scotland. A further proof of a northerly 
 current is found in the fact that the conglomerates of 
 Tebay (further south-east) contain stones and boulders 
 that have certainly come from the Lake District, and their 
 percentage increases up to a certain point as the beds are 
 traced southward. Again, along the Pennine escarpment 
 the basement beds contain stones derived from the Lower 
 Old Red Sandstone of the Cheviot district, and these must 
 also have come from the north. 
 
 Mr. G-oodchild concludes, therefore, that the drift of the 
 pebbles was from the northward, and, as regards the sub- 
 mergence of the land, he holds that there was a ridge of 
 high ground extending across the Pennine and Lake Dis- 
 tricts, which formed an island at the time when the con- 
 glomerates and sandstones were being deposited, but that 
 it was rapidly submerged and entirely covered by the sea 
 before the epoch of the Yoredale Beds. The position of 
 the ridge can be determined by drawing a line round the 
 points where the Lower Carboniferous Beds are thinnest. 
 Thus the beds below the Toredale series, along the Pennine 
 range, are found to be thinnest in Teesdale (400 feet) and 
 
 G 
 
82 PALAEOZOIC TIME. [CHAP, VI. 
 
 near Milburn, where they are 700 feet ; northward they 
 rapidly thicken to over 2,000 feet, and southward they 
 increase to 1,800, and then to 2,500 at the head of the 
 Eden Valley. Along the border of the Lake District the 
 thickness of the same beds varies from 400 to 800 feet, 
 except at Mell Fell, where the basal conglomerates seem to 
 fill an old hollow ; north-west of Appleby they are about 
 900 feet, but south-eastward they gradually increase to 
 2,500 feet. 1 
 
 Another ridge which was gradually submerged in Lower 
 Carboniferous times seems to have lain under Ingleborough, 
 and probably extended thence to the north-east. The total 
 thickness of the sub-Yoredale Beds near Ingleborough is 
 about 650 feet, of which 150 may be assigned to the basal 
 conglomerate ; while, to the north, the thickness near Sed- 
 burgh is 2,400, and to the west and south-west it is over 
 3,000 feet. 
 
 With regard to the southern uplands of Scotland, it has 
 already been suggested that the western part of this region 
 was in connection with the Hiberno-Cambrian land, and we 
 have also seen that it probably supplied rock-fragments to 
 the conglomerates in the north of England ; but the great 
 valley through which the river Nith now runs seems to 
 have existed before the Carboniferous period, and to have 
 been occupied by a long gulf or inlet of the Carboniferous 
 Limestone sea, as testified by the fossils which occur in the 
 bands of limestone associated with the red sandstones and 
 shales of the Thornhill basin. The similarity of these 
 deposits to those of Ayrshire makes it probable that they 
 were continuous, and that the inlet was soon converted into 
 a strait which separated the upland region into two parts. 
 
 The central uplands then became an island, and the red 
 sandstones and conglomerates which form the base of the 
 
 1 For all these particulars I am indebted to Mr. Goodchild. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 83 
 
 Carboniferous system can be traced all round it. They 
 sweep over the high ground on the borders of Berwick and 
 Haddington, and seem to have covered the whole of the 
 Lammermuir Hills, but the central uplands of Lanark, 
 Peebles, and Selkirk may have remained above water 
 during the greater part of the period. There is, indeed, 
 no evidence that they were ever submerged. The Calci- 
 ferous sandstones are clearly shore-beds deposited on an un- 
 even and irregular surface, and it would be very unsafe to 
 assume that those at the higher levels must have been suc- 
 ceeded by the whole series of Carboniferous rocks which 
 are found to the north or south of such tracks. It is pro- 
 bable that the sandstones represent higher and higher parts 
 of the series as they near the higher ground, and that the 
 conglomerates which fringe the Carboniferous rocks were 
 formed on the slope of a sinking coast-line. There is, in- 
 deed, positive evidence in the south of Edinburgh that the 
 whole of the beds below the Limestone group have thinned 
 out, for south of Magbiebill an outlier of the limestone 
 rests directly on the Lower Old Red Sandstone. Here, 
 therefore, more than half the thickness of the Scotch Car- 
 boniferous system has died out against the slope of the 
 southern uplands, so that it becomes highly probable that 
 this hill region was above water till the close of the Lime- 
 stone epoch, and if the Millstone Grit was formed during 
 a slight upheaval, as many think, the land area would then 
 have been somewhat enlarged. 
 
 It may be advisable to point out that the existence of the 
 great boundary fault does not invalidate the above conclu- 
 sion. If this were a post-Carboniferous dislocation it might 
 be said that the ground on the upcast side was so much 
 lower in Carboniferous time that it might have been covered 
 by the limestones ; as a fact, however, the limestones and 
 coal-measures are not broken by the fault, and in the south 
 of Edinburgh it seems to have given rise to a steep bank 
 
84 PALAEOZOIC TIME. [CHAP. VI. 
 
 or cliff, against which the limestones and their associated 
 strata were laid down. 1 
 
 Lastly, can we gather any evidence regarding the northern 
 limits of the Carboniferous sea and the probability of con- 
 tinental land existing in that direction ? There is, in the 
 first place, good reason to believe that land existed outside 
 the north-west portion of Ireland : in Galway and Mayo 
 the Carboniferous limestones are everywhere bordered by 
 conglomerates, and it is stated that these are on the horizon 
 of the Upper Limestones ; that near Oughterard the conglo- 
 merates and sandstones graduate eastward through shales 
 into limestones along the line of strike, and that in other 
 localities the limestones themselves contain pebbles up to 
 the size of a bean. 
 
 The northern part of Donegal seems to have formed 
 part of this land, for the Carboniferous rocks occurring in 
 South Donegal and North Tyrone seem to pass northward 
 into shales and sandstones. 
 
 On the west coast of Scotland, in the district of Morvern 
 (Argyleshire), there is a small tract of Carboniferous 
 sandstone let down by faults among the older rocks. This 
 is believed to be of Coal-measure age, and was probably 
 laid down in a gulf which penetrated the northern mass 
 of land between Donegal and the Highlands of Scotland ; 
 we may suppose, therefore, that a similar gulf existed in 
 Lower Carboniferous times, but a smaller and less exten- 
 sive one. 2 
 
 There is every reason to suppose that the Highlands 
 were land throughout the Carboniferous period. I am in- 
 formed by Mr. H. M. Cadell that the oil-shales of the 
 Lothians are mostly replaced by grits and sandstones in 
 the north of Fife, and that everything indicates an approach 
 to land in that direction. Indeed, the persistent recurrence 
 
 1 "Mem. Geol. Surr. Scotland, Expl. of Sheet 24," p. 17. 
 
 a By mistake it has been carried too far north in the map, Plate IV, 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 85 
 
 of shallow and fresh-water conditions throughout the Scot- 
 tish Carboniferous series proves the neighbourhood of 
 land, and leads to the conclusion that the area of the 
 Devonian Lake Caledonia was converted at this period into 
 a land-locked gulf which stretched north-eastward into 
 continental land, and was only connected with the more 
 open sea by narrow channels between the mainland and the 
 islands above indicated. We may reasonably suppose that 
 many rivers emptied themselves into this gulf, especially 
 at its north-eastern end, and the nature of the deposits 
 indicates that the subsidence was at times more than 
 counterbalanced by the amount of material brought down 
 by the rivers, so that the eastern part of the gulf was some- 
 times silted up and converted into tracts of low swampy 
 land, enclosing large sheets of water, which were sometimes 
 fresh, sometimes brackish, and only occasionally invaded 
 by the sea. 
 
 2. Geographical Restoration. 
 
 The evidence for most of the coast-lines delineated on 
 Plate IV. has been amply discussed, and it only remains to 
 show reason for the lines to the east and south of England, 
 and to give some account of the conjectured extent of the 
 continent which lay to the north of the British Carboni- 
 ferous sea. 
 
 The entire absence of Carboniferous rocks over the whole 
 of the Scandinavian peninsula, except the extreme south of 
 Sweden, renders it highly probable that this area formed 
 part of the northern continent, and was united to the 
 Scottish Highlands; the southern border of this land 
 seems to have crossed the centre of Denmark, and a pro- 
 longation of this line would strike the coast of Yorkshire. 
 Professor Hull suggests that it trended south-westward 
 and joined that of the land which lay over the midland 
 
86 PALEOZOIC TIME. [CHAP. VI. 
 
 counties of England, but there is really no evidence for 
 this, and I think it is more likely to have had an outline 
 such as that shown on the map, broken into a series of 
 bays and estuaries, like that in which the Scotch measures 
 seem to have been formed. 
 
 As there was evidently land to the north-west both of 
 Scotland and Ireland, and as this was probably united to 
 the Scoto- Scandinavian land, it is evident that the greater 
 part of the North Atlantic must have been land at this 
 time. When, moreover, we remember that no rocks of 
 Carboniferous Limestone age have yet been found in any 
 part of Iceland or Greenland, nor in any part of northern 
 Canada, nor in the Arctic regions south of G-rinnell Land 
 (where it does occur), the facts seem to be greatly in favour 
 of Professor Hull's view that at this period a large conti- 
 nent occupied the whole area of the North Atlantic, and 
 extended from Finland on the east to the Rocky Mountains 
 on the west. We cannot attempt to define its southern 
 border across what is now the Atlantic Ocean ; this, of course, 
 must ever remain a matter of pure speculation, but it is 
 puerile to make this a ground of objection to Professor 
 Hull's hypothesis. 1 Those who have adopted the theory of 
 the permanence of continents and of oceans throughout all 
 geological time are naturally biassed against the existence 
 of an Atlantic continent at any period, but those who think 
 that continents may last long without being absolutely 
 permanent see no reason why large parts of the Atlantic 
 region should not have been land more than once in the 
 course of geological time. 
 
 Professor Green has published a representation of 
 Lower Carboniferous geography which differs in some im- 
 portant particulars from Professor Hull's, and from the 
 restoration I have attempted in Plate IV. There are two 
 
 1 Physical History of the British Isles," 1880, p. 37, and " Trans. 
 Roy. Dub. Sue.," ser. ii. vol. iii. p. 305. 
 
PLATE IV. GEOGRAPHY OF THE LOWER CARBONIFEROUS PERIOD 
 
 (LOWER SHALE AND LIMESTONE EPOCH). 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 87 
 
 features in his map 1 which do not seem to be in any way 
 warranted by the facts. In the first place he unites the 
 land which lay off the north-west of Ireland with that of 
 the southern uplands of Scotland, and makes the Scottish 
 Carboniferous basin open north - westwards into the 
 Atlantic. Probably he would now be inclined to alter 
 this part of his map, for there is certainly much more 
 reason for connecting the North Irish land with that of 
 the Scottish Highlands than with the southern uplands, 
 and the probability of such a connection stands altogether 
 apart from the question of continental land in the North 
 Atlantic. 
 
 In the second place he shows continuous land, not only 
 from the east across the centre of England, but from 
 Wales south-westward to join a mass of land between 
 Ireland and France, so that the sea which covered the 
 south of England is depicted as having no connection 
 whatever with that which covered Ireland and the north 
 of England. Now this is hardly probable ; that land may 
 have existed to the south of Ireland I am prepared to 
 admit, but there is no evidence for connecting it with the 
 central barrier, while the close correspondence between 
 the deposits of South Ireland and those of South Wales 
 and Devon is quite against such a view and in favour of 
 a continuous water-space between them. The prepon- 
 derance of mechanical deposits, and the absence of any 
 thick limestones in the Carboniferous series of Devonshire, 
 points to deposition in a muddy sea which received the 
 sediment brought down by large rivers draining con- 
 tinental land. This land could only have been to the west 
 or south-west, and the overlap of the Culm-measures on 
 to the Petherwyn Beds in Cornwall makes it probable that 
 the shores of this land were not far distant, and may even 
 have traversed part of Cornwall. More information, how- 
 1 " Coal, its History and Uses," 1878, p. 38. 
 
88 PALEOZOIC TIME. [CHAP. VI. 
 
 ever, is required before more than the general position of 
 this land can be indicated. Thus until recently it was 
 supposed that the Lower Carboniferous series was not 
 represented in Brittany. Dr. Ch. Barrois, 1 however, has 
 shown that certain slates and sandstones, which were 
 previously regarded as Devonian, are really of Carboni- 
 ferous age. They are based on conglomerates and volcanic 
 rocks, and are overlapped southward by the Coal-measures, 
 which rest on the Lower Devonian near Quimper. Land, 
 therefore, existed in the south of Brittany during Lower 
 Carboniferous time, but whether it was an island or a 
 promontory from a western Atlantic continent we can- 
 not yet decide. 
 
 The sea which lay over so large a part of what are now 
 the British Isles stretched eastward through the north-east 
 of France, Belgium, Germany, Poland, and Eussia, cover- 
 ing, therefore, a large part of the present continent of 
 Europe, and thence extending toward the North, Pole by 
 way of Bear Island and Spitzbergen, but it seems to have 
 been bounded on the south by a more or less continuous 
 belt of land through France, Switzerland, Bavaria, Bohemia, 
 and Hungary. 
 
 Thus it seems clear that the sea in which our Carboni- 
 ferous beds were deposited was not an open sea or ocean, 
 but a land-locked sea, comparable, to some extent, with the 
 Mediterranean of the present day ; it was studded with 
 islands of various sizes, its coast-line formed a series of 
 gulfs and promontories, and it communicated with other 
 seas by means of one or more narrow straits like the Straits 
 of Gibraltar. 
 
 1 " Bull. Soc. Geol. de France," ser. iii. t. xiv. pp. 661, 665. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 89 
 
 3. Physical Conditions indicated by the Successive 
 Deposits of the Period. 
 
 The Carboniferous rocks differ in certain respects from 
 those of the preceding and succeeding systems, and they 
 exhibit characters which can only have resulted from 
 a general uniformity of physical conditions having prevailed 
 over very large areas of the earth's surface. The same 
 general succession of deposits is met with, not only over the 
 whole of the British Islands, but over the greater part of 
 Northern Europe and of central North America. Further- 
 more, the fauna and flora of the Carboniferous rocks are 
 everywhere similar, and are everywhere persistent through- 
 out a great thickness of strata. Of the marine fossils a 
 few species are indeed confined to the lowermost beds, and 
 a few to the highest marine beds to beds, in fact, which 
 were formed when the physical conditions were undergoing 
 a change, and when the forms would necessarily be most 
 liable to variation; a few other species those, namely, 
 which were the chief contributors to the formation of the 
 limestones are naturally most abundant in those lime- 
 stone masses ; but by far the larger number of species have 
 a very great vertical range, many of them extending from 
 top to bottom of the marine series, and even appearing in 
 the essentially freshwater and estuarine strata above and 
 below, wherever the temporary prevalence of marine con- 
 ditions led to the formation of limestone. 
 
 As regards the process of sedimentation which went on 
 in the central sea which covered the northern part of 
 England, Professor Green has given an account, from which 
 I extract the following : l " This Mediterranean sea had a 
 fringe of shallow water around its margin, and deep depres- 
 sions in its central portion. Bound its edges deposits were 
 
 1 " The Yorkshire Coalfield," by Green and Russell, " Mem. Geol. 
 Survey," p. 24. 
 
90 PALAEOZOIC TIME. [CHAP. VI. 
 
 formed, mainly of mud and sand, though every now and then 
 calcareous animals established themselves in sufficient num- 
 bers to give rise to beds of limestone. At a certain distance 
 from the shore all the sediment sank down to the bottom, 
 and beyond this limit the water was bright and clear, and 
 the only deposit consisted of accumulations of the hard, 
 calcareous parts of marine animals which are now pure 
 limestone. 
 
 " In the deep hollows the deposits of limestone reached 
 a great thickness ; over the ridges which parted the hollows 
 it was not so thick. This will explain how it is that the 
 Carboniferous Limestone shows such great variations in 
 thickness at different spots. The growth of the limestone 
 gradually filled up the deeper parts of the sea, and at last 
 the area became as shallow throughout as it had been 
 originally only at its edges. The mixed deposits of sand- 
 stone, shale, and impure limestone, which had at first been 
 confined to the neighbourhood of the shore, now extended 
 themselves over nearly the whole marine tract, and the 
 deposition of the Toredale rocks began 
 
 " After a time a further important change took place. 
 Either by the outlets becoming blocked up, or by the 
 upheaval of a portion of the bottom, the land-locked area 
 in which the lower marine portion of the Carboniferous 
 rocks was deposited became cut off from communication 
 with the open ocean .... and converted into a fresh- 
 water lake or a large estuary which received the waters 
 of rivers flowing from the north, east, and south. 1 In 
 this freshwater, or brackish area, the Millstone Grit and 
 Coal-measures were deposited. When the water was at its 
 shallowest, currents piled up banks of sand, or drifted coarse 
 materials over the bottom, and shot them down into hollows, 
 
 1 It would be better described as an immense delta or fenland, in- 
 cluding many large lagoons and wide channels, surrounded by swamps 
 which were never much above the level of the sea. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 91 
 
 and thus formed lenticular beds of sandstone, or washed 
 down and spread out pre-existing sandbanks, and gave rise 
 to more regular sandstone beds. When the depth was 
 greater, only fine mud was brought into the water, which 
 settled down into more regularly bedded and uniform 
 deposits of shale. 
 
 " The subsidence which allowed of the growth of the 
 mechanically-formed deposits did not go on without inter- 
 ruption. Every now and then a pause occurred, and when- 
 ever this happened, the water became filled up, and there 
 was a tendency to the formation of low, swampy flats." 
 He proceeds to point out that wherever a land surface was 
 formed, vegetation quickly sprang up, and furnished the 
 material for beds of coal. When these swampy flats were 
 again submerged, fresh deposits of mud and sand covered 
 the rich, carbonaceous soil, and entombed the trees and 
 plants which grew in it. 
 
 Such, according to Professor Green, is a brief sketch of 
 the submarine changes attendant upon the gradual depo- 
 sition of the Carboniferous rocks of Yorkshire, and it is 
 applicable to all other regions where a similar series of 
 beds is found. As far as the earlier members of this 
 series are concerned, there is nothing very remarkable in 
 their mode of formation. They are simply masses of 
 limestone, shale, and sandstone which can be paralleled by 
 similar groups in other geological systems ; but the upper 
 members were accumulated under conditions which have 
 been much less frequently repeated during geological 
 time conditions, indeed, which have never prevailed again 
 in the European area to the same extent as they did in the 
 Carboniferous period. It will, therefore, be worth while 
 to describe these conditions a little more fully, and to 
 see what conclusions may be drawn from them as to the 
 general state of physical geography towards the close of 
 this long period. 
 
92 PALEOZOIC TIME. [CHAP. VI. 
 
 Professor Green elsewhere points out that the great 
 series of beds which compose the divisions of the Mill- 
 stone Grit, the Lower and the Middle Coal-measures, have 
 so many common characteristics " that it is impossible to 
 resist the conclusion that they were all three formed under 
 substantially the same conditions, and that these condi- 
 tions were altogether different from those which gave rise 
 to the Carboniferous Limestone and the Yoredale rocks." l 
 He thinks the change was caused by the blocking up of the 
 communications between the inner and the outer sea, so 
 that the former was converted into a large freshwater lake, 
 but though this might account for the succession in the 
 principal English and Scotch coalfields, it is far too local 
 an explanation to account for the Irish, French, Belgian, 
 and other European coal-measures. 
 
 In the first place let us consider the formation of the 
 Millstone Grit, which consists principally of coarse sand- 
 stones, the grains of which are mostly angular and very 
 little worn, and are sometimes of very large size. The 
 sandstones are in fact coarser than those which occur in 
 the Yoredale Beds below or in the Coal-measures above, 
 and Prof essorGreen remarks that the Upper Carboniferous 
 series exhibits a gradational change in the texture of its 
 sandstones from the Millstone Grit upwards. The Mill- 
 stone Grits are not only coarse and massive, but are re- 
 markably persistent over large areas. " In the Lower Coal- 
 measures sandstones still play an important part ; but as a 
 rule they are neither so coarse nor so strong as those of the 
 Millstone Grit, and they vary much more from place to 
 place both in thickness and texture. Throughout a large 
 portion of the Middle Coal-measures thick sandstone beds 
 are conspicuous by their absence, and when such beds do 
 occur, they are, with very few exceptions, fine in grain ; 
 they are also markedly local, and can seldom be traced 
 1 " Coal, its History and Uses," 1878, p. 50. 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 93 
 
 continuously for more than a few miles" (op. cit., p. 
 60). 
 
 Now the persistence of the coarse-grain sandstones and 
 the impersistence of the finer-grain beds is just the oppo- 
 site of what might be expected, and is indicative of some 
 special conditions during the formation of the Millstone 
 Grit. Such widely-distributed and coarse-grained sand- 
 stones can hardly have been deposited during a con- 
 tinuance of the subsidence which led to the formation of 
 the underlying shales and limestones ; moreover, the thick- 
 ness of the grits does not increase in the direction of the 
 mainland, but is greatest in the south-western part of 
 what may be called the central basin, where the Yoredale 
 group is also the thickest. 
 
 The distribution of the grits, indeed, is such as to 
 suggest that the materials were derived from the detrition 
 of the land which formed the southern shore of this central 
 basin, and the position of which has already been indicated. 
 Thick lenticular masses of Millstone Grit occur both on 
 the north and south sides of this land tract, the centre of 
 one great mass being in Lancashire and that of another in 
 the Bristol coalfield. From the Burnley coalfield, where 
 the sandstones alone are over 2,000 feet thick, the grits 
 thin away to the north-east through Yorkshire and Dur- 
 ham, and to the south-east through Derbyshire, but less 
 rapidly to the south, being still thick and coarse in North 
 Staffordshire, within thirty miles of the shore-line. More- 
 over, in the extreme north-east (Northumberland) their 
 texture is so fine that they are actually less coarse than 
 some of the Lower Carboniferous sandstones of that area ; 
 it is clear, therefore, that the material did not come from 
 that direction. In the Bristol coalfield the Millstone G-rit 
 is 950 feet thick, and though the group thins in all direc- 
 tions, yet the coarse grits are conspicuous along the north 
 side of the South Wales coalfield and in the Forest of 
 
94 PALAEOZOIC TIME. [CHAP. VI. 
 
 Dean, while in Grower and Devon they are represented by 
 shales and fine-grained sandstones. In Ireland the Mill- 
 stone Grit is seldom coarse-grained, but usually consists of 
 flagstones which are never more than 650 feet thick. Such 
 being the arrangement of these grits, it is difficult to see 
 from what quarter they could have been derived, except 
 from the central and eastern parts of the large island 
 shown on PI. IV., these parts being probably its highest 
 and steepest districts. 
 
 Even then, however, we cannot understand the super- 
 position of coarse sandstones upon a limestone and shale 
 series without assuming that great changes took place in 
 the physical geography of the area. During the formation 
 of the lower limestones the brooks which drained this part 
 of the land can hardly have carried any sediment to the 
 sea, their waters must have been clear, and the rainfall 
 must have been small; later on, however, they seem to 
 have carried both mud and sand, and eventually their 
 volume and velocity were so increased that they could 
 transport coarse sand to very great distances. I see only 
 one way in which such a change could be brought about, 
 and that is by a general and considerable elevation of the 
 area, raising the central parts of the island into those 
 atmospheric regions where rain, frost, and wind are most 
 vigorous and incessant in their action. The effects of up- 
 heaval in altering the character of the sediment deposited 
 round the land would be greater in the case of a rocky 
 island with steep slopes, which were prolonged beneath the 
 surrounding sea, than on the mainland, where the mountain 
 ranges would seldom be so close to the coast-line. In the 
 latter case much of the sand would be deposited before the 
 rivers reached the sea ; but in the former the streams and 
 torrents would not only be able to carry the sand to the 
 sea, but the issuing currents would sweep it to some dis- 
 tance from the shore. Further, not only would the velocity 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 95 
 
 of the streams be increased with the increase of the rain- 
 fall, but as the area of the land enlarged and the depth of 
 the sea became less, the sand would be carried farther and 
 farther out over the sea-bottom, and would be arranged in 
 sandbanks and shoals by the sea-currents. So far did this 
 filling-up process go on, that parts of the sea-floor actually 
 became shallow enough for the growth of terrestrial plants, 
 and seams of coal occur in the highest part of the Mill- 
 stone Grit of Lancashire. 
 
 There seems, therefore, good reason for supposing that 
 the Millstone Grit marks a general and rather rapid up- 
 heaval of the whole British region, but it is quite certain 
 that this movement exhausted itself before the commence- 
 ment of the true Coal-measures, for these were undoubtedly 
 formed during a gradual and general subsidence, and it is 
 interesting to note how this subsidence is attended by a 
 reverse change in the texture of the sandstones (see p. 92). 
 As Professor Green remarks, 1 " The gradual subsidence 
 and the ceaseless wear and tear of atmospheric denudation 
 gradually lowered the elevated tracts, so that they were 
 acted on less vigorously by subaerial agencies ; at the 
 same time the rivers, descending by gentler gradients, lost 
 by degrees the power of moving coarse heavy detritus. So, 
 with the lapse of years, the amount of sandy sediment 
 gradually grew less and less, and sandstones formed a 
 gradually decreasing item in the deposits in process of 
 formation." 
 
 In spite of the submergence, however, large tracts of the 
 sea-floor were repeatedly silted up and converted into 
 marshy flats, for the best authorities are agreed that coal- 
 seams are land-growths, though the tracts on which they 
 were accumulated were evidently never raised much above 
 the mean level of the sea. It is not improbable that the 
 coal-seams mark pauses in the progress of the subsidence, 
 1 Coal, its History and Uses," p. 61. 
 
96 PAL2EOZOIC TIME. [CHAP. VI. 
 
 while the occasional occurrence of a marine band indicates 
 a time when the downward movement was more rapid than 
 usual, causing the waters of the open sea to overflow the 
 wide alluvial levels. Lastly, from the overlap of the Coal- 
 measures, and from the wide extension which individual 
 coal-seams attain in the Middle Coal-measures, we may 
 infer that the area of the marshy flats on which the coal- 
 plants flourished was being continually increased at the 
 expense of the higher and drier inland districts which they 
 surrounded. 
 
 We know what a wide extension the Coal-measures had 
 over the British area, and that what are now separate 
 basins or coalfields were originally connected and con- 
 tinuous areas. But this great development of Coal-mea- 
 sures is by no means peculiar to Britain ; coalfields are 
 found in many parts of the Continent, notably in France, 
 Belgium, Germany, and Russia, everywhere presenting a 
 similar aspect and a similar succession of measures, making 
 it certain that they belonged to one natural province or 
 geographical area. 
 
 We must conclude, therefore, that over a large part of 
 what is now Europe there existed vast tracts of alluvial 
 land but little above the sea-level, the conterminous deltas, 
 in fact, of the rivers which drained the surrounding land, 
 just as Holland is the conterminous delta of the Rhine, 
 Meuse, and other rivers. It is as if an area as large, or 
 larger, than that covered by the Mediterranean Sea, were 
 slowly silted up and converted into one enormous swamp. 
 To bring about such a result there must have been many 
 rivers of large size emptying themselves into this sea, 
 rivers comparable to the largest which now exist in the 
 world, and for the supply of such rivers the surrounding 
 continents must have possessed mountain ranges compar- 
 able to those of America and Central Europe, and must 
 have been watered, by a copious rainfall. 
 

 CHAP. VI.] CARBONIFEROUS PERIOD. 97 
 
 Again, although the area of deposition was constantly 
 widened by subsidence, yet the detritus brought down from 
 the higher to the lower levels was always sufficient to 
 counterbalance this depression. Further, it would appear 
 that all this material must have been obtained from the 
 surface of the land, and transported by fluviatile agencies, 
 for there could have been very little coast-erosion round 
 the borders of this land-locked sea. 1 Rain and frost must 
 therefore have been constantly at work on the surface of 
 these continents, disintegrating and dislodging the rocks of 
 which they were composed, while the rivers would be 
 chiefly employed in carrying off the detritus so prepared, 
 for the continued depression would have diminished their 
 erosive capacity by lowering the slope of their channels. 
 
 It is a geological axiom that deposition is a measure of 
 detrition, and we may see, therefore, in this enormous mass 
 of sediments a measure of the detrition which took place, 
 and of the amount of material removed from those portions 
 of the great Carboniferous continent which drained into 
 that sea whose limits have been indicated above. 
 
 Now the time necessary for the progress and consumma- 
 tion of all these natural operations must have been enor- 
 mous, and yet the geographical changes must have been so 
 slight and so slowly accomplished throughout this great 
 length of time that they did not materially alter the rela- 
 tive positions of land and sea, or interrupt the process of 
 swamp formation ; this, then, is the peculiar and remark- 
 able point in Carboniferous history which I desire to im- 
 press upon the reader's mind, that it was a period of in- 
 ternal quiescence, a period in which terrestrial disturbances 
 were at a minimum, and consequently when the surface 
 agencies of change were able to continue their course of 
 action to a greater extent than usual. Now their course of 
 
 1 It is very probable that, as in the modern Mediterranean, the rise 
 and fall of the tide in this sea was very small. 
 
98 PALEOZOIC TIME. [CHAP. VI. 
 
 action is such, that if they were allowed full play, and were 
 not checked or balanced by uplifting movements, every 
 continent would gradually be reduced in height, and worn 
 down to a level but little above that of the sea, while the 
 surrounding waters would be choked and shallowed by the 
 materials poured into them from the wasting land. It 
 would appear, therefore, that the Carboniferous was a period 
 when this theoretical result was more nearly approached than 
 it ever has been before or since ; when the continents were 
 gradually lowered by the combined action of detrition and 
 depression, the area of high ground being continually dimi- 
 nished, but the area of low-lying, swampy ground at or about 
 the sea-level being continually increased, so that at the close 
 of the period similar physical conditions as to climate, rain- 
 fall, surface slopes, soil and vegetation, seem to have pre- 
 vailed throughout the greater part of the northern hemi- 
 sphere. 
 
 Such a condition of affairs will account for the remark- 
 able uniformity of life which prevailed throughout the 
 Carboniferous period, a fact to which attention was called 
 on p. 89. The geographical changes being so slight, and 
 during the earlier portion of the period consisting chiefly 
 in an extension of the marine areas at the expense of the 
 land, we may suppose that the seas retained their same 
 relative positions and connections throughout an enormous 
 lapse of time, and that the denizens of these seas spreading 
 far and wide through the broadening water-spaces found 
 everywhere a similarity of conditions that enabled them to 
 nourish and survive without change or variation. Later 
 on, when the seas were shallowed by the continued depo- 
 sition of material derived from the continents, and when 
 the higher land was everywhere encircled by a wide belt 
 of low-lying jungle and swampy ground, intersected by 
 sluggish water-ways and lagoons, the conditions would be 
 exactly those where nature would present a monotonous 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 99 
 
 and uniform aspect, and where the plants and animals 
 which had established themselves would be likely to main- 
 tain their existence unchanged so long as the same con- 
 ditions prevailed. 
 
 In this way it seems possible to explain the widespread 
 uniformity of Carboniferous deposits and the remarkable 
 persistence of Carboniferous forms of life, phenomena 
 which make this period a unique portion of geological time. 
 It is as if we were contemplating the close of one great 
 phase of the world's history, when the forces and causes 
 which had hitherto been operative were exhausted and 
 quiescent, when evolution was nearly at a standstill, and 
 the world was allowed a grand pause before entering on 
 the mighty changes which were to commence a new order 
 of things, and to give such a powerful impulse to the 
 development and differentiation of the earth's inhabitants. 
 
 There now remains for consideration only the epoch of 
 the Upper Coal-measures, which exhibit certain important 
 points of difference from the measures below. The shales 
 and sandstones are generally of red, purple, brown, or 
 green tints ; the clays are often red, or mottled red and 
 green ; the coal-seams are thin and less numerous ; the 
 fossil remains are entirely freshwater, and there are occa- 
 sional beds of limestone which are not made up of organic 
 remains, but are either compact and creamy -looking when 
 freshly broken, or are porous and spongy in texture. All 
 these circumstances are indices of an important change 
 in the conditions of deposit. 
 
 Red and mottled clays occur in other formations under 
 conditions which show them to be lacustrine deposits. 
 The colouring matter of the sandstones is ferric oxide, 
 every grain being coated with a thin pellicle of such 
 oxide, as if the colouring matter had been deposited upon 
 every grain as it came to rest at the bottom of a stagnant 
 body of water. Now such an amount of iron oxide is not 
 
100 PALEOZOIC TIME. [CHAP. VI, 
 
 likely to accumulate in waters which opened into the sea, 
 but might do so in lakes and swampy tracts which were 
 not traversed by any strong currents, and were never in- 
 vaded by the sea- waters. 
 
 Professor Green, indeed, thinks that these beds were 
 formed in lake's which had no outlet at all, and the waters 
 of which were gradually concentrated by evaporation. He 
 points to the limestones as having characters which re- 
 semble those of limestones formed by precipitation from 
 saturated solutions, and such saturation is certainly almost 
 an impossibility in a lake with an outlet. 
 
 There is another fact which tells greatly in favour of 
 this theory, namely, that the Upper Coal-measures are 
 frequently found to lie unconformably on those below, and 
 the Middle measures have sometimes suffered a considerable 
 amount of erosion before the upper group was deposited 
 on them. Such a relation implies terrestrial movement, 
 and probably an elevation of those districts in which it is 
 found, and when we consider the enormous extent of 
 nearly level ground which must have existed in the time of 
 the Middle Coal-measures, it is easy to see that very slight 
 uplifts would be sufficient to convert large areas into 
 shallow lake-basins. 
 
 Moreover, the known geographical distribution of these 
 red Coal-measures has considerable significance. They 
 occur in all the Midland coalfields, as well as in Lanca- 
 shire, Yorkshire, Cumberland, and Scotland ; but the so- 
 called Upper Coal-measures of South Wales and Gloucester- 
 shire are not red, neither is there any such group in 
 Ireland or in Devonshire. It may, of course, be said that 
 the true Upper Coal-measures are absent by denudation 
 in these last-mentioned districts, but in South Wales the 
 Coal-measure series is thicker than in any other district, if 
 the upper group is deducted ; and the fact remains that 
 the red measures are only known to occur in the country 
 
CHAP. VI.] CARBONIFEROUS PERIOD. 101 
 
 which lies to the north and east of the island barrier. 
 Now a reference to the map (Plate IV.) will show that this 
 area over which the red rocks occur is exactly that which 
 is most likely to have been converted into a lake or group 
 of lakes by a very slight geographical change. The sea 
 had probably always been shallow at the northern and 
 eastern ends of the central island, and a union of these to 
 the mainland would completely enclose the area in ques- 
 tion, isolating it from the other areas of deposition, and 
 converting it into such a shallow lacustrine basin as the 
 facts seem to indicate. Such appears to have been the 
 last stage in the Carboniferous geography of the British 
 area. 
 
CHAPTER VII. 
 
 DYASSIC OR PERMIAN PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 T7XCEPT in the north-east of England the Dyassic 
 IJ rocks occur only in fragmentary strips and patches 
 along the borders of the Coal-measure basins. This dis- 
 connected mode of occurrence is partly due to the over- 
 stepping of the Trias, under which many areas of Dyas are 
 buried and concealed, and partly of course to the removal 
 of large portions by erosion. Their limitation, however, to 
 certain districts and their entire absence in the south of 
 England are facts due to the conditions under which they 
 were originally deposited. The Dyassic beds exhibit two 
 distinct lithological f acies, which may be called the eastern 
 and western types; the latter being the more local and 
 abnormal, while the former is similar to that which pre- 
 vails in Germany. 
 
 A. The rocks of the eastern type are supposed to under- 
 lie the greater part of East Yorkshire, Lincoln, and Not- 
 tingham, and their outcrop forms a continuous strip of 
 ground, between the Carboniferous and Triassic strata, 
 from the coast of Durham, southward by Auckland, Ripon, 
 and Pontefract, to the neighbourhood of Nottingham. 
 
 The beds are thickest and most purely calcareous in 
 Durham, where they consist almost entirely of dolomite 
 or magnesian limestone. The basement beds are soft sand 
 and calcareous shale of variable thickness ; the limestones 
 
CHAP. VII.] DYASSIC PERIOD. 103 
 
 above are 450 feet thick, and the highest beds (proved in 
 the borings at Middlesbrough) include deposits of rock- 
 salt and gypsum. 
 
 In South Yorkshire the main mass of limestone is 270 
 feet thick, and there are marls and limestones above to a 
 thickness of 140 feet ; but in Notts all the beds are greatly 
 attenuated, the total thickness near Mansfield being pro- 
 bably about 200 feet, of which not more than 100 are 
 limestone, and parts of this are really calciferous sand- 
 stones. Near Nottingham it is still less, and seems to be 
 on the point of thinning out when it is overlapped by the 
 Trias. 
 
 A boring near Newark and about fifteen miles east of 
 the outcrop at Mansfield is important as throwing much 
 light on the lithological changes of the formation. This 
 section proves that while the limestones remain about the 
 same, the formation thickens eastward by an increase of 
 the marls and shales, the calcareous marls at the base 
 having a thickness of 118 feet, as compared with fifteen 
 or thirty feet in Notts. A boring through the Trias at Ow- 
 thorpe, in the south of Notts, proved the Dyas to be want- 
 ing there, and passed directly into Coal-measures. These 
 facts show that, in Notts at any rate, the Dyas thins 
 rapidly both southward and westward, whence we may 
 conclude that land lay in both these directions, an infe- 
 rence which is confirmed by the collection of pebbles found 
 in the basal breccia, which comprises not only pebbles of 
 Carboniferous limestone and fragments of sandstone and 
 shale from the underlying Coal-measures, but pebbles of 
 slate, quartz, and quartzite, which have probably been 
 derived from the rocks of Charnwood Forest. 
 
 B. Passing now to the western districts, we may select 
 that of the Cumberland Plain or Vale of Eden as the 
 most complete and important. Here and elsewhere on the 
 west side of the Pennine chain there is very little lime- 
 
104 PALAEOZOIC TIME. [CHAP. VII. 
 
 stone, and the rocks consist chiefly of red sandstones with 
 occasional beds of calcareous breccia. Between Carlisle 
 and Penrith there are two massive sandstones, the lower 
 about 1,000 feet, and the upper about 1,500 feet thick, 
 separated by a zone of red shales. Near Appleby the 
 lower sandstone contains thick beds of breccia (locally 
 called brockram), consisting of pebbles derived from the 
 Carboniferous limestone, and the red shales have at their 
 base bands of magnesian limestone and impure coal. 
 
 On the west side of the Lake District there is another 
 strip of Dyas, but the lower (Penrith) sandstone is not 
 present, and the basal beds at St. Bee's Head consist of 
 magnesian limestone with fossils (11 feet thick) resting on 
 a thin breccia of limestone fragments. 
 
 Northward, in Dumfries and Ayr, rocks similar to the 
 Cumberland sandstones are found occupying several basin- 
 like depressions, and resting partly on Carboniferous and 
 partly on the older rocks. In Nithsdale and the valley of 
 the Ayr sheets of porphyrite and volcanic ash are inter- 
 stratified with the sandstones, and even the stumps of the 
 volcanic vents from which these materials were ejected 
 can be identified. 
 
 Returning to England, small detached patches of Dyassic 
 deposits occur at intervals round the coalfields of Lan- 
 cashire, Denbighshire, Shropshire, Staffordshire, Warwick- 
 shire, and Worcestershire. The Lancashire beds resemble 
 those of Cumberland, consisting of a red sandstone over- 
 lain by red marls, shales, and limestones, with fossils of 
 the Magnesian Limestone type. 
 
 Denbigh and North Staffordshire exhibit rather a dif- 
 ferent type, the beds being similar in both districts, and 
 consisting of dark red and purple sandstones, with red 
 marls and bands of cornstone ; these beds are only slightly 
 unconformable to the Upper Coal-measures. 
 
 In the Shrewsbury, Bridgenorth, and South Stafford- 
 
CHAP. VII.] DYASSIC PERIOD. 105 
 
 shire districts there is a similar set of beds, divisible into 
 three stages, the middle one (from 200 to 400 feet thick) 
 consisting of breccia and conglomerate, sometimes cal- 
 careous, and sometimes chiefly composed of felspathic ma- 
 terials large blocks of felstone, syenite, and volcanic tuff 
 occurring with boulders of quartz rock, limestone, sand- 
 stone, and slate; all these have probably been derived 
 from the Archaean, Cambrian, and Silurian rocks that un- 
 derlie the Dyas and Trias of the Midland counties. 
 
 Further south still the Lower Sandstones disappear, and 
 at Church Hill, in Worcestershire, the breccia lies directly 
 on the Coal-measures, the fragments composing it being 
 very large and angular, and identifiable with rocks of 
 Cambrian and Silurian age lying to the north-west. Small 
 outliers of similar breccia rest against the Silurian of the 
 Abberley Hills, and the most southerly is that at Haffield, 
 at the southern end of the Malvern range. 
 
 This incoming of breccias southward with a thinning out 
 of the lower beds is unequivocal evidence of a close ap- 
 proach to the southerly limit of the area in which these 
 deposits were formed, and the breccias are also a proof 
 that the shores were steep and rocky. 
 
 The only other districts in England where rocks of this 
 age occur are, (1) Warwickshire, where they consist of red 
 sandstones and marls, with occasional beds of calcareous 
 breccia and conglomerate, the whole supposed to be nearly 
 2,000 feet thick, and (2) Anglesey, where similar beds to 
 a thickness of 400 feet overlie the Coal-measures. 
 
 In Ireland three small patches occur in Ulster, fossi- 
 liferous magnesian limestone existing at Cultra, on Belfast 
 Lough, and at Tullyconnel in Tyrone, and Boulder beds, 
 with a limestone breccia at the base, rest on the Carboni- 
 ferous Limestone of Armagh. The blocks in the Boulder 
 beds are chiefly grits and sandstones derived from the 
 Silurian and Old Red Sandstone districts that lie to the 
 north-west. 
 
106 PALAEOZOIC TIME. [CHAP. VII. 
 
 2. Geographical Restoration. 
 
 In Chapter VI. the Carboniferous period was described 
 as one of quiescence, during which the forces of terrestrial 
 disturbance were in abeyance ; but, as a calm precedes a 
 storm in the atmosphere around our earth, and a great 
 stillness often forebodes an earthquake, so in the earth's 
 history a period of quiet deposition and rock-making has 
 often been followed by a period of disruption and rock- 
 destruction. Certain it is that the calm of Carboniferous 
 times was followed by an epoch of great disturbance in the 
 European and Atlantic areas, causing movements which 
 produced very great geographical changes in the northern 
 hemisphere, and resulted in the breaking up of the Car- 
 boniferous continents, and in the upheaval of the ground 
 which had been covered by the Carboniferous seas. 
 
 At the close of the Carboniferous period there seem to 
 have been important upheavals of land on either side of 
 the great Atlantic continent. The Alleghany Mountains in 
 America date from this epoch, as do also the series of 
 domes, ridges, and faulted upheavals which make up the 
 Pennine chain or " backbone " of England. It appears 
 certain that the principal earth-throes, those which pro- 
 duced the more important disturbances of the Carboni- 
 ferous rocks in Britain, occurred during the unrepresented 
 period of time which intervened between the Coal-measures 
 and the Dyas. The stratigraphical relations of the latter 
 to the former make it clear that the disturbances, which 
 bent the Coal-measures into the basin- shaped forms they 
 now present, took place before any Dyas sic strata were 
 deposited. These movements resulted in the development 
 of a double system of anticlinal and synclinal axes, one 
 set running north and south, the other nearly east and 
 west. It is impossible to say whether this double system 
 of axes was formed simultaneously, or whether one set was 
 
PLATE V. GEOGRAPHY OF THE DYAS OR PERMIAN PERIOD. 
 
CHAP. VII.] DYASSIC PERIOD. 107 
 
 formed first and the second set by a separate and subse- 
 quent movement, but it is certain that the interference or 
 combination of these axes has produced the broad basins 
 in which the Coal-measures are now found. 
 
 The system of east and west flexures is particularly well 
 marked in Ireland, the pre-Dyassic movements acting most 
 forcibly over the northern and southern districts, and 
 raising the whole central mass of country between them. 
 In the south of England there is a set of ridges similar to 
 those in the south of Ireland, passing from Devon and 
 Somerset beneath the newer rocks of the southern counties 
 into Belgium and the north of France. It is also very 
 likely that the tract of Palaeozoic rocks which underlies 
 the east of England was elevated at this epoch. 
 
 Simultaneously with these upheavals it is very probable 
 that the ancient Atlantic continent was broken up, sub- 
 merged, and converted into an open ocean ; the depression 
 of this Atlantic area being in fact the proximate cause of 
 the upheavals on either side. Such, according to Professor 
 Hull, was the genesis of the North Atlantic Ocean, 1 and, 
 apparently, it has never ceased to be an ocean from that 
 time to the present day, though throughout the Mesozoic 
 periods there was a large continuous tract of land to the 
 west of England, of which Ireland, Wales, and Cornwall 
 are now the sole remnants. 
 
 It may, in fact, be said that the rock-masses out of which 
 Ireland, Scotland, and the greater part of England have 
 been hewn, were now, for the first time, brought into con- 
 nection as a compact mass of land. The greater part of 
 this land region lay to the south and west, spreading from 
 the north of France, through the south of England, to 
 Wales and Ireland, and thence, by way of the Hebrides, 
 to Scotland and the Border counties. It was not Britain, 
 
 1 " Physical History of the British Isles/' 1882, p. 44. 
 
108 PALAEOZOIC TIME. [CHAP. VII. 
 
 but a West-European continent, which presented a con- 
 tinuous front to the Atlantic, considerably to the west of 
 what are now the shores of France and Ireland. 
 
 It is now time to seek for the boundaries of the seas 
 and lakes in which the Dyassic sediments were deposited. 
 The open Mediterranean sea of the Carboniferous period 
 appears to have been converted into a large inland sea, 
 like the Caspian of the present day, surrounded by a 
 rocky and hilly continent, on which grew trees and plants 
 of various kinds. Many of these plants are closely allied 
 to those of the Carboniferous, but species belonging to the 
 Yew and Fir tribes, which nourish on dry ground, pre- 
 ponderate over the reeds, ferns, and gigantic lycopodia 
 which flourished in the Coal-measure swamps. 
 
 The western part of this inland sea stretched across the 
 centre of what is now the North Sea, and covered a portion 
 of north-eastern England, and its actual margin seems to 
 have lain only a little to the west of the outcrop which now 
 runs through the counties of York and Nottingham, curv- 
 ing round to the eastward beneath the south of Lincoln- 
 shire. If the Pennine range formed a continuous barrier 
 in Dyassic times, its eastern slope must naturally have 
 been the shore-line of the Magnesian Limestone sea, and 
 such is now the prevalent opinion ; but it is only fair to 
 state that the geologist who first studied the uplifts of the 
 Pennine range l came to the conclusion that they were post- 
 Dyassic. Strong arguments were, however, subsequently 
 adduced by other writers to show that he was mistaken, 
 and it is perhaps desirable that the reasons for the view 
 here adopted should be stated seriatim? 
 
 1. The flexures of the South Yorkshire and Derby coal- 
 fields are certainly pre-Dyassic, and as their major axes 
 
 1 Hull, in " Quart. Journ. Geol. Soc.," vol. xxv. p. 171. 
 
 2 See Wilson, " Geol. Mag.," ser. 2, vol. vi. p. 500, and Teall, vol. 
 vii. p. 349. 
 
CHAP. VII.] DTASSIC PERIOD. 109 
 
 are parallel to the central Pennine axis, we may safely 
 assume that they were both formed at the same time. 
 
 2. After crossing the Millstone Grit area of central 
 Yorkshire, the outcrop of the Dyas again passes on to 
 Coal-measures in the south of Durham, showing that 
 all the flexures between the two coal-basins were pre- 
 Dyassic. 
 
 3. No Dyassic outliers occur at any distance west of the 
 main escarpment, and no fragments of Magnesian Lime- 
 stone have been found in the Triassic rocks, as might 
 have been expected if that limestone had passed over the 
 Pennine axis, and had been subjected to erosion in Trias- 
 sic times. 
 
 4. On the other hand, fragments of Carboniferous Lime- 
 stone are said to have been found both in the Dyassic 
 breccias and in the Triassic sandstones, which would prove 
 that this limestone had already been bared along the 
 Pennine axis. 
 
 5. The Dyassic rocks on opposite sides of the Pennine 
 range are very dissimilar, the thin local beds of niagnesian 
 limestone on the western side bearing no comparison with 
 the massive dolomites of the eastern tract, while the red 
 sandstones are essentially a feature of the western dis- 
 tricts. 
 
 It might perhaps be doubted whether the range formed 
 a complete barrier, and whether there was not communica- 
 tion between the two areas of deposition by means of a 
 narrow strait across the centre of Yorkshire. The only 
 piece of evidence in favour of such a communication is the 
 occurrence of Magnesian Limestone fossils in the lime- 
 stones of Lancashire and Ireland, but as both the eastern 
 and western areas were uplifted portions of the Carboni- 
 ferous sea, the same forms of life are likely to have re- 
 mained in both, even if one was rapidly isolated by the 
 upheaval of a barrier. On the whole, therefore, the 
 
110 PALEOZOIC TIME. [CHAP. VII. 
 
 balance of evidence is against the existence of any con- 
 necting strait, and in favour of the view that the Pennine 
 range then formed a continuous and lofty chain of hiHs 
 reaching from Derbyshire to the Scottish border, so that 
 the western Dyassic lake was entirely isolated from the 
 waters of the inland sea to the east. 
 
 Neither can I see that there is any strong evidence for 
 the existence of the east and west barrier-ridge through 
 Cheshire, which is supposed by Professor Hull to have 
 divided the western area into two distinct lakes. The 
 differences between the Lancastrian and Salopian deposits 
 are really unimportant, and are quite compatible with 
 their having been formed in different parts of the same 
 lake. The width of the ridge, as shown on Professor 
 Hull's map, 1 is so small, that it is not likely to have been 
 a permanent barrier, but it may have been a subaqueous 
 ridge separating the lake into two basins, much as the 
 Mediterranean is divided into two basins by the ridge 
 between Sicily and Africa. 
 
 This lake then appears to have extended from Warwick- 
 shire and the Malvern Hills to the Firth of Clyde, a 
 distance of 280 miles, with an extreme width of 100 miles, 
 so that it was about the size of the modern Lake Huron. 
 It spread over the counties of Warwick, Worcester, Staf- 
 ford, Salop, Cheshire, and Lancashire, and over the eastern 
 part of the Irish Sea. It encircled the Lake District, 
 which must have risen as a rocky island out of its waters ; 
 it covered the valley of the Eden and Solway Firth, and 
 arms of it ran up the valleys of the Nith and Annan, and 
 probably for some distance up the Firth of Clyde, while 
 westward a gulf extended into Ireland as far as Armagh 
 and Dungannon in Tyrone. How far it reached westward 
 and southward beyond Anglesey we have no means of 
 
 1 Physical History of the British Isles," pi. riii. 
 
CHAP. VII.] DYASSIC PERIOD. Ill 
 
 knowing, but there is no reason to suppose it extended 
 far, for Wales and Ireland were doubtless connected by a 
 tract of high mountainous land. 
 
 The slopes surrounding this lake seem in most places to 
 have been steep, and the rivers running into it were conse- 
 quently rapid, carrying down quantities of sand, and in 
 some regions large stones and boulders, as in the breccias 
 of the Midland counties. The size of the transported 
 boulders in these breccias, their angularity, and the occa- 
 sional striation of their surfaces, suggested to Professor 
 Eamsay that they had been carried by floating ice. Many 
 of the fragments can be identified with Welsh rocks, and 
 it is highly probable that the Welsh mountains were then 
 much more lofty than at present, and that snow may have 
 accumulated on them in sufficient quantity to form glaciers. 
 Some of these may have reached the level of the lake, and 
 torrential streams bursting from others may have been 
 equally active in carrying down the rock-fragments quarried 
 from the frosty regions above. 
 
 On the northern borders of the lake volcanic forces came 
 into play, and lava-flows with beds of volcanic ash were 
 interbedded with the lacustrine sandstones (see p. 104). 
 
 From the thickness of the mechanical deposits in this 
 north-western lake, and the rarity of magnesian lime- 
 stones, we may infer that many streams and rivers ran 
 into it, bringing a constant supply of fresh water and pre- 
 venting the formation of chemical deposits. The north- 
 eastern lake, on the other hand, seems to have suffered 
 from evaporation and concentration ; possibly, also, the 
 waters poured into it contained a larger proportion of salts 
 in solution. At any rate, there are good reasons for re- 
 garding the Dyassic dolomites as direct chemical deposits, 
 although the process of precipitation cannot be imitated in 
 our laboratories. 
 
 The analogy between the conditions of the modern Gas- 
 
112 PALEOZOIC TIME. [CHAP. VII. 
 
 plan Sea and those which appear to have prevailed in the 
 sea of the Magnesian Limestone has been pointed out by 
 Sir A. Ramsay. Just as the Caspian is believed to have 
 been originally connected with the Arctic Ocean, and as its 
 fauna is really a marine assemblage, so also the inland 
 sea which in Dyassic times stretched from England into 
 Germany seems to have been isolated from the main 
 oceans of the period, the introduction of new species and 
 genera being thus prevented, so that the fauna was only a 
 dwarfed and modified remnant of Carboniferous life. 
 
 Mr. E. Wilson suggests the following as the probable 
 sequence of events in the north-eastern basin. 1 After 
 indicating the formation of the basement sands, he says 
 " After a time the waters would become sufficiently satu- 
 rated to cause dolomitic materials to be thrown down to 
 some extent, which, commingled with the sand and mud, as 
 also with the large supplies of ferrous carbonate likewise 
 brought down by the rivers, would give rise to the blue- 
 coloured plant-bearing dolomitic sandstones and shales of 
 the Marl Slate series. During this stage, mechanical de- 
 position predominated, on the whole, over chemical pre- 
 cipitation. . . . Somewhat suddenly (however) this state of 
 things came to an end. 2 Chemical precipitation now began 
 to predominate, and the formation of the white and yellow 
 Dolomites commenced." In the north this precipitation 
 continued uninterruptedly, but the intercalations of shale 
 and marl in the southern part of the area point to the in- 
 flowing of large rivers from the land which then existed 
 over the east of England. It was clearly these southern 
 
 1 " The Permian Formation of N.E. England, Midland Xat.," vol. iv. 
 
 2 The change, as Mr. Wilson suggests, was probably due to pro- 
 gressive subsidence, which, by diminishing the altitude of the surround- 
 ing land, while increasing the area of evaporation, would tend to promote 
 condensation of the lake-waters, and the consequent precipitation of 
 mineral matter in solution. 
 
CHAP. VII.] DYASSIC PERIOD. 113 
 
 rivers that brought down the argillaceous material of the 
 Marl Slates and Middle Marls, derived doubtless from a 
 wide surface of Coal-measures then undergoing destruc- 
 tion, while the streams from the west, being smaller but 
 more rapid, may be credited with the introduction of the 
 Yorkshire " quicksands." 
 
CHAPTEE VIII. 
 
 TRIASSIC PERIOD. 
 
 1. Stratigraphical Evidence. 
 
 THE lie of the Triassic rocks is different from that of 
 any of the Palaeozoic systems. In England their out- 
 crop is nearly continuous from the southern to the northern 
 coasts ; in Gloucestershire it is very narrow, but it broadens 
 out over the Midland counties, and stretches northward 
 over tracts of considerable width on either side of the 
 Pennine range. The one tract meets the sea in Durham, 
 the other in Lancashire, but both must originally have ex- 
 tended much farther north, for detached areas of Trias 
 occur in Cumberland and Dumfries, also in the north-east 
 of Ireland, in the Inner Hebrides, and in the north-east of 
 Scotland on the Moray Firth. 
 
 The Triassic strata are everywhere unconformable to the 
 rocks on which they rest ; they extend far and wide beyond 
 the edges of the Dyassic beds, and run up many of our 
 wider valleys as if the principal hill-ranges of England 
 were then already in existence, as indeed they doubtless 
 were. The Coal-measures and older Palaeozoic rocks had 
 been bent into troughs, basins, and ridges, and had suffered 
 enormously from erosion and detrition before the Triassic 
 beds were deposited upon them, so that in most parts of 
 the country these beds rest upon a surface of erosion which 
 had been previously formed across the tilted edges of the 
 Palaeozoic rocks. 
 
3 
 
 a rn 
 
 6 
 
 it 
 
 
116 NEOZOIC TIME. [CHAP. VIII. 
 
 The manner in which the Trias, with the succeeding 
 Jurassic and Cretaceous strata, rests upon a floor of Palaeo- 
 zoic rocks is shown in fig. 3. This is a section from the 
 valley of the Severn near Gloucester, through the counties 
 of Gloucester, Oxford, Buckingham, and Hertford, to the 
 valley of the Lea at Ware. It does not pretend to be an 
 accurate representation of the subterranean structure of 
 the country in respect to details, for the Palaeozoic rocks 
 have only been touched at two places along the line of 
 traverse, viz., at Burford and Ware. At the former place 
 Coal-measures were found at a depth of 1,080 feet from 
 the surface, the Trias being here only 424 feet thick, and 
 belonging wholly to the Upper, or Keuper division ; at 
 Ware, Silurian rocks were found below the G-ault, so that it 
 is clear that the Trias and all the Jurassic strata must thin 
 out against the slope of Palaeozoic rocks indicated in the 
 diagram, though how far eastward each division extends is 
 not yet known. It should also be stated that the flexuring 
 and faulting of the Palaeozoic rocks represented in the dia- 
 gram is quite theoretical, and is only intended to convey a 
 general idea of the way in which these rocks are supposed 
 to lie. 
 
 In Ireland the Trias occupies a similar position, resting 
 on an uneven floor of Ordovician and Carboniferous rocks, 
 and being covered conformably by Jurassic and Cretaceous 
 strata. In Scotland also its stratigraphical relations are 
 similar. 
 
 The British Trias is divisible into two series, the 
 lower being usually called the Bunter, and the upper the 
 Keuper, from their German correlatives. There is no re- 
 presentative of the marine member of the German Trias, 
 and the British Trias is certainly not a marine formation. 
 
 The Bunter Beds occupy three distinct areas of deposi- 
 tion : one in Devonshire, which probably extends some way 
 beneath Dorset and the English Channel ; a larger one in 
 
CHAP. VIII.] TRIASSIC PERIOD. 117 
 
 the Midland counties, and stretching thence through 
 Cheshire into Lancashire ; and a third on the eastern side 
 of the Pennine chain in Nottingham, Lincoln, and York, 
 but this seems to have been connected with the Midland 
 area by a narrow neck between Nottingham and Derby. 
 The Southern and Midland areas were separated by a broad 
 ridge of Palaeozoic rocks, which was not submerged till the 
 epoch of the Keuper, or Upper Trias. 
 
 In Devonshire the Bunter consists of coarse breccias and 
 sandstones, the blocks and stones in the former having 
 been derived from the neighbouring Devonian and Car- 
 boniferous rocks. They have evidently been accumulated 
 under the action of rapid currents, being obliquely and 
 irregularly bedded, so that though their thickness appears 
 to be about 1,000 feet, their real depth at any one place 
 may not be more than 500 feet. Over these coarse-grained 
 beds are some 400 feet of marls and sandstones, succeeded 
 by 80 feet of pebble beds, which are sometimes compacted 
 into a conglomerate. 1 In many places the pebbles consist 
 of Devonian limestone and sandstone, like those found in 
 the underlying breccias, but elsewhere, and especially at 
 Budleigh Salterton, there are pebbles of sandstone and 
 quartzite which are different from any Devonshire rocks, 
 but some of which are identical in character and fossil 
 contents with certain rocks occurring in Normandy and 
 Brittany, viz., the Gres Armoricain and the G-res du May. 
 
 It has, therefore, been surmised that these pebbles were 
 brought either from France or from land connecting France 
 with Cornwall, and since destroyed. This inference, how- 
 ever, has been somewhat weakened by the finding of similar 
 pebbles in the Trias of Staffordshire, and even if the 
 
 1 These are placed by Mr. Ussher in his upper division of the 
 Devonshire Trias ; but as the whole series is continuous, I prefer to 
 treat them with the lower beds, as being comparable to the Banter 
 pebble beds of the Midland counties. 
 
118 NEOZOIC TIME. [CHAP. VIII. 
 
 pebbles did originally come from the southward, it is by 
 no means certain that they were transported from their 
 original source in Triassic times. On this point Mr. H. B. 
 Woodward remarks : " Considering their hard nature, it 
 seems doubtful whether they were shaped in Triassic times. 
 Such smooth pebbles of grit or quartzite are rarely found 
 in the red conglomerates and breccias bordering the older 
 rocks ; hence the idea occurs that the Budleigh pebbles may 
 have been derived from some old (? Carboniferous) conglo- 
 merate." x 
 
 The Bunter of the Midland counties consists of bright 
 red and yellow sandstones with a central zone of pebble 
 beds, and it is a remarkable fact that these pebble beds 
 are more constant and have a wider extension than the 
 sandstones above and below. Each division varies much 
 in thickness, but the whole attains a maximum thickness 
 in Cheshire of 1,800 feet ; it is nearly the same in Shrop- 
 shire, but thins southward through Worcestershire, and 
 dies out on the east side of the Abberley Hills. Thence 
 the subterranean boundary of the Bunter probably passes 
 eastward through Warwick to the neighbourhood of Rugby, 
 and thence northward into Leicestershire. The lower 
 sandstones thin out in Staffordshire along a line from 
 Dallaston and Stafford to Wolverhampton ; the upper 
 sandstones die out a little further east and north-east, so 
 that in Leicestershire a,nd Derbyshire only the pebble beds 
 remain. In the Nottingham district the Bunter division 
 is never thick, the upper sandstones being absent, the 
 lower sandstones being from 25 to 100 feet, and the pebble 
 beds being about 300 feet thick near Nottingham ; they 
 can be traced as far as Doncaster, but the pebbles become 
 fewer and smaller toward the north, and the rock seems 
 to pass into an orange- coloured sandstone, which can be 
 traced as far as Ripon. 
 
 1 " Geology of England and Wales," second edition, p. 239. 
 
CHAP. VIII.] TBIASSIC PERIOD. 119 
 
 The same is the case with the pebble beds in Lancashire ; 
 near Liverpool they consist of reddish brown pebbly sand- 
 stones, and are more than 600 feet thick, but the pebbles 
 are small and scattered, and the group is said to die out 
 between Ormskirk and Preston. In Ireland (Antrim) 
 certain red and yellow sandstones are referred to the 
 Bunter division, but no beds of this age have been recog- 
 nized in Scotland. 
 
 Observations on the lithological characters of these sand- 
 stones and pebble beds have disclosed several important 
 facts. Certain beds of friable sandstone have been de- 
 scribed by Dr. Sorby and Mr. J. A. Phillips, under the 
 name of " Millet-seed beds," the grains of quartz and 
 felspar of which they consist being so completely worn 
 and rounded that the disintegrated sand flows through the 
 fingers as easily as seed or shot. Such sandstones are fre- 
 quent in the Lower Bunter, and occur also in the upper 
 division. Ordinary sandstones consist of more or less 
 angular grains (see p. 4), and Mr. Phillips, after having 
 examined a number of modern sands, states that " none of 
 them, excepting such as had long been subjected to the 
 wearing effects of wind action, were found to resemble 
 those of the Millet-seed sandstones in having all their 
 grains reduced to a pebble-like form. Among these the 
 grains of blown desert-sands most completely resemble 
 those of millet-seed sandstones." ] From these facts we 
 may infer that such sandstones are of seolian formation, 
 and that during the epoch of the Bunter Beds large desert 
 tracts, with their usual accompaniment of blowing sands, 
 existed in the British region. 
 
 The pebble beds have been studied by Professor Bonney 
 
 and Mr. W. J. Harrison. The majority of the pebbles 
 
 consist of vein-quartz or quartzite, and Professor Bonney 
 
 finds that the quartzites differ from any English rock that 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxxvii. p. 27. 
 
120 NEOZOIC TIME. [CHAP. VIII. 
 
 he is acquainted with, but that they closely resemble the 
 quartzites of the Highlands of Scotland, pebbles of which 
 are common in the Old Eed and Lower Carboniferous con- 
 glomerates of central and southern Scotland. He has also 
 found pebbles of a quartz-felspar grit, which can only be 
 compared with the harder parts of the Torridon sandstone, 
 so that he thinks the currents which carried the pebbles 
 came from the north. 
 
 Mr. Harrison, however, argues that the pebbles have 
 been derived from the Palaeozoic rocks which underlie the 
 Trias in the Midland and Eastern counties. He points to 
 the fact that the pebbles are largest in the Midlands, and 
 decrease in size as the beds are traced northward, and he 
 has also found quartzites which contain Devonian fossils 
 similar to those in the Budleigh Salterton pebbles. These 
 are undoubtedly strong arguments against the northern 
 derivation of the pebbles, at any rate against the idea of 
 their having all been transported from the north in 
 Triassic times. 
 
 It is possible, however, that both observers may be right, 
 and that the conflict of opinion may be more apparent 
 than real. Professor Bonney rests his opinion chiefly upon 
 the remarkable correspondence of the quartzites with certain 
 rocks which only occur in situ in Scotland, but he admits 
 that they are not likely to have been derived directly from 
 these rocks in Triassic times. In point of fact, they may 
 have had more than one resting-place before reaching their 
 present location ; some of them may have been primarily 
 embedded in the Lower Old Eed Sandstone, and may from 
 this have been washed into the Upper Old Eed and Car- 
 boniferous conglomerates. Now the latter are known to 
 contain rocks of Scotch origin as far south as the Isle of 
 Man, Westmoreland, and north-west Yorkshire. It is 
 quite possible, therefore, that such pebbles may have been 
 carried as far south as Derbyshire, and may, for ought we 
 
CHAP. VIII.] TEIASSIC PERIOD. 121 
 
 know, be exposed beneath the Trias in the south of Derby- 
 shire. 1 Quartz and quartzite are exactly the rocks which 
 would survive long transportation and repeated transference 
 from one formation to another, in which process the more 
 destructible Scotch rocks would be destroyed. 
 
 We must therefore confess that our present knowledge 
 does not enable us to arrive at any definite conclusion as 
 to the exact position of the strata from which the pebbles 
 of the Bunter conglomerates were derived. It is certain, 
 however, that, whether they came from the north or the 
 south, they can only have been distributed over the area 
 they now occupy by the action of strong currents. What 
 currents these can have been will be discussed in the 
 sequel. 
 
 Coming next to the Keuper, or Upper Triassic beds, we 
 find that these have a much wider extension than the 
 Bunter beds. There is generally a certain amount of un- 
 conformity between the two divisions, the surface of the 
 Bunter being often uneven and eroded, and the base of the 
 Keuper in the Midland counties being always a breccia, 
 pebble bed, or conglomerate. Over this base there are red, 
 yellow, and white sandstones, and these are succeeded by 
 flaggy sandstones and sandy marls passing up into red 
 marls with beds of rock-salt and gypsum. 
 
 The Lower Keuper sandstones are generally soft and 
 fine-grained, often micaceous and laminated, and frequently 
 current-bedded. There are, however, some beds of coarser 
 sandstone with worn and rounded grains, which may have 
 been wind-borne sands. The red and brown flaggy sand- 
 stones, which are generally known as " the waterstones," 
 exhibit clear signs of having been deposited in the shallow 
 
 1 It is more likely perhaps that the exposures of the Carboniferous 
 pebble beds lay more to the south-east, beneath Northampton and 
 Huntingdon, as 1x5 wer Carboniferous sandstones occur beneath the 
 Trias near Northampton. 
 
122 NEOZOIC TIME. [CHAP. VIII. 
 
 waters of a lake. Ripple-marks, sun-cracks, rain-prints, 
 worm-markings, and the footprints of reptiles are common 
 on their surfaces. 
 
 The red and mottled marls are such as would be formed 
 in the deeper parts of the lake, and they sometimes include 
 beds of sandstone, which contain remains of plants, fish, and 
 small Crustacea (Estheria). The thick beds of rock-salt 
 and gypsum which occur in the marls attest the saline 
 nature of the lacustrine waters. 
 
 The Keuper deposits, like those of the Bunter, are 
 thickest in Cheshire, where they are believed to be over 
 3,000 feet thick. Thence they seem to thin in every direc- 
 tion, but most rapidly to the south and south-east. In 
 Worcestershire the Keuper is only about 900 feet thick, in 
 Gloucester and North Somerset it is much less, and is in 
 some places only represented by shore-beds consisting of 
 sandstone and conglomerate, the pebbles and grains of 
 which are held together by a dolomitic cement, whence it 
 is known as the Dolomitic conglomerate. Elsewhere there 
 are sandstones and marls from 200 to 400 feet thick, the 
 latter containing bands of red and grey limestone, the 
 material of which has clearly been derived from the Car- 
 boniferous Limestone. In West Somerset and Devon the 
 marls and sandstones again thicken to nearly 1,500 feet. 
 
 If we proceed south-eastward from Cheshire, we find the 
 Keuper beds diminished to less than 1,000 feet in South 
 Staffordshire, and to about 700 feet in Warwickshire ; 
 while borings near Northampton disclose the very eastern 
 limits of the formation, its thickness there varying from 
 24 to 82 feet. The Gayton boring is especially interesting, 
 for beneath 60 feet of red Keuper marl and sandstone 
 12 j feet of breccia was found, consisting of large blocks of 
 carboniferous limestone and sandstone embedded in a 
 sandy matrix. Under it was 9J feet of marl and shale, 
 which rested on an eroded surface of a limestone belonging 
 
CHAP. VIII.] TEIASSIC PERIOD. 123 
 
 to the Lower Carboniferous series. Such a breccia can 
 only have been formed in close proximity to a shore-line, 
 and the blocks are probably the debris of a cliff that over- 
 hung the waters of the Keuper lake. 
 
 Southward the Keuper marls and sandstones are known 
 to pass beneath Oxfordshire, where their thickness is about 
 400 feet, and it is highly probable that they stretch con- 
 tinuously through Berks and Hants, and beneath the Eng- 
 lish Channel into Normandy, where there is a small area 
 of Trias, consisting of conglomerates, sandstones, and 
 marls. In Jersey also there is a small patch of conglo- 
 merate which is believed to be Triassic. 
 
 Whether Trias exists beneath the London Basin is a 
 moot point ; because it is not yet settled whether the red 
 sandstones and marls which have been found in the deep 
 borings at Richmond, Crossness, and Kentish Town belong 
 to this formation or to the Old Bed Sandstone. The red 
 and yellow sandstones of the Trias and the Upper Old Red 
 are certainly very similar to one another, but it may be 
 observed that no thick deposit of red marl, such as forms 
 the mass of the Keuper, has been met with in these 
 borings, although the red strata traversed at Richmond 
 were over 200 feet thick, and those at Kentish Town 188 
 feet. Further, the Keuper Sandstone group generally 
 maintains a uniform character over considerable areas, 
 whereas the characters of the strata below London vary 
 largely ; at Richmond they are soft variegated sandstones 
 and marls, at Crossness hard quartz sandstones with red 
 and grey shales, and at Kentish Town variously coloured 
 sandstones and clays, with a thin bed of conglomerate. 
 These variations might of course be due to the proximity 
 of a shore-line ; but, considering all the circumstances, 
 and especially the great distance of the sites south-east of 
 any place where Trias is known to exist, I incline to the 
 opinion of Professor Prestwich and others that these 
 
124 NEOZOIC TIME. [CHAP. Till. 
 
 strata belong to the Old Eed Sandstone, and not to the 
 Trias. 
 
 Northward the Keuper beds extend far beyond the 
 limits of the Bunter. In Cumberland and the north-east 
 of Ireland their characters are similar to those of the 
 Midland counties, but on the west coast of Scotland the 
 strata are rather different. Their thickness here varies 
 considerably, but in Mull, Mo'rvern, and parts of Ross it 
 is about 1,000 feet, and the whole probably belongs to the 
 Keuper. The lower part consists of coarse breccias, con- 
 glomerates, and sandstones, and the upper half exhibits a 
 variable succession of red marls, with bands of concre- 
 tionary limestone and of hard white or greenish sand- 
 stone. The breccias and conglomerates were doubtless 
 accumulated in the same manner as those of Devonshire, 
 and the higher beds seem to have been deposited in the 
 quiet waters of a lake. 
 
 2. Geographical Restoration. 
 
 The unconformity which exists between the Dyas and the 
 Trias, wherever the latter rests on the former, points to a 
 period of elevation and disturbance, which probably in- 
 volved the total desiccation of the Dyassic seas and lakes, 
 and the conversion of their floors into wide tracts of dry 
 desert land. The only beds in England which appear to 
 be of intermediate age are certain deposits of rock-salt, 
 gypsum, and limestone, which have been found below the 
 Trias in deep borings near Middlesbrough-on-Tees. The 
 limestones contain Dyassic fossils, but lie between beds of 
 rock-salt, the upper of which seems to be conformably over- 
 lain by Trias sic sandstones ; none of them appear along the 
 outcrop, and they must, therefore, occupy a limited area. 
 They may have "been formed in one of the restricted lake- 
 basins which doubtless existed during the gradual drying 
 
CHAP. VIII.] TEIASSIC PERIOD. 125 
 
 up of the Magnesian Limestone sea. It is certain that the 
 general elevation was accompanied by differential move- 
 ments producing areas of comparative depression and 
 elevation ; thus a further uplift of the Pennine range took 
 place, and the Dyassic beds on either side received a slight 
 tilt, so that the lower beds of the Trias were laid down 
 across their edges, and overstepped them on to the Car- 
 boniferous rocks. Consequently that beds of intermediate 
 age should exist beneath the Trias to the eastward is only 
 what might have been expected. 1 
 
 That the continued upheaval caused a great alteration 
 in the physical conditions of the European region is evident 
 from the great changes which took place in its inhabitants. 
 The Dyassic forms of life, which were mostly survivals of 
 Carboniferous forms, were completely exterminated and re- 
 placed by a different fauna and flora. Among plants new 
 genera of ferns and conifers appeared, Cycads began to 
 flourish, and Equisetum replaces the Carboniferous and 
 Permian Catamites. The fish and reptiles which inhabited 
 Triassic waters all, except Palceoniscus, belong to new and 
 distinct genera ; crocodiles and Dinosaurs now first appear, 
 and before the end of the period a marsupial mammal 
 made its way into the British area. 
 
 1 Professor A. H. Green's review of Lebour's " Geology of Northum- 
 berland and Durham " (in " Nature," July 28, 1887) came to hand after 
 this chapter was written. He takes exactly the same view of the 
 Middlesbrough beds, and observes "It seems likely that toward the 
 end of the Permian period unequal subsidence produced hereabouts a 
 depression in the bed of the water; that as now happens elsewhere 
 under similar conditions, the Permian lake became largely laid dry, so 
 that the water remained only in this and perhaps other similar basins ; 
 and that from the highly concentrated solutions which remained in 
 these lakelets local deposits of a strongly chemical character were pre- 
 cipitated." To this I will only add that the " Gypseous Shales " of the 
 Carlisle basin may belong to the same period of transition, and may 
 have been formed in a similarly limited basin, for some geologists class 
 them with the Trias and some with the Dyassic rocks. 
 
126 NEOZOIC TIME. [CHAP. VIII. 
 
 During the formation of the Bunter deposits it seems 
 probable that the whole European region, including the 
 North Sea and Baltic areas, formed one large continent, in 
 which there may have been both salt and freshwater lakes, 
 but that all such water- spaces were then reduced to a 
 minimum. We know, however, that there was a greater 
 amount of elevation in the northern than in the southern 
 part of the European region, and that in the Alpine area 
 it was soon followed by submergence ; a sea of considerable 
 depth covered this area which is now so mountainous, and 
 its waters at one time extended northward as far as Ger- 
 many and the eastern borders of France. The Muschel- 
 kalk limestones thin out in the Vosges country, and are 
 not found to the westward of a line between Luxembourg 
 and the Cote d'Or. The north-east of France and the 
 region of the Ardennes seem at this time to have con- 
 stituted a tract of high and mountainous ground, which 
 probably extended northward through Belgium l and the 
 east of England, and thus separated the British from the 
 Germanic area of deposit. 
 
 The formation of the Keuper deposits marks another 
 change, and we may suppose that the depression of the 
 Triassic continent, which is indicated by the extension of 
 the Muschelkalk sea, was continued in such a manner that, 
 though the sea was still excluded from the northern areas, 
 the courses of the principal rivers which had previously 
 
 1 Messrs. Cornet and Briart have attempted to estimate the height to 
 which this land rose above the sea-level of the period, and place it at 
 from 16,000 to 20,000 feet. They arrive at this result by a considera- 
 tion of the complicated system of fractures and flexures in the axis of 
 Artois (Belgium). They attribute these to a succession of movements, 
 and describe the several stages in the process by which the present 
 collocation of rock masses was in their opinion accomplished 5 but their 
 views are somewhat cataclysmic, and they do not seem to have allowed 
 sufficiently for the removal of material by detrition during the process 
 of faulting, flexure, and elevation. (" Ann. Soc. Geol. Belg.," iv. p. 71.) 
 
CHAP. VIII.] TRIASSIC PERIOD. 127 
 
 found their way into the southern sea were altered, and 
 their waters deflected into the depressed areas, forming large 
 inland seas or salt lakes. Professor Ramsay compares the 
 geographical conditions of northern Europe during Triassic 
 times to those of central Asia at the present time, where 
 from the Caspian Sea for 3,000 miles to the eastward and 
 far south toward the Himalayah there is a comparatively 
 rainless district in which all the lakes are salt, except those 
 which have an outlet to some lower lake. 
 
 Confining our view now to the area of the British Islands, 
 we find in early Triassic times three separate areas of de- 
 position (see p. 116) : one in the south, where the Devon 
 and Dorset Trias was formed ; one in the north-west over 
 the site of the western Dyas lake ; and one in the north- 
 east, which was probably a long and narrow tract bounded 
 on each side by a range of mountains. 
 
 Let us first consider the conditions which prevailed in 
 the southern area at this epoch. The deposits which form 
 the lower part of the Trias in this district are such as 
 might be accumulated in a lake that was bounded by high 
 and rocky land ; the succession of breccias, sandstones, and 
 marls is strongly suggestive of deposition in water, and 
 there can be little doubt that the lake-basin was bounded 
 on the west and south by land of a rocky and mountainous 
 character, which extended continuously from Devon and 
 Cornwall into the north of France. On the east and north 
 the lake was enclosed by a projecting mass of land which 
 stretched from France and Belgium through the south- 
 east of England, and was united to Wales by an extension 
 of the Mendip Hills ; but as the ground on the north was 
 subsequently covered by the Keuper marls, we may infer 
 that it was lower than that which lay to the west, south, 
 and east. 
 
 The western coasts of the lake seem to have been espe- 
 cially steep and rocky, the mountains probably coming 
 
128 NEOZOIC TIME. [CHAP. VIII. 
 
 close to its shore, just as the Maritime Alps border the 
 shores of the Biviera. It seems, indeed, as if the condi- 
 tions under which the lower breccias and pebbly sand- 
 stones of Devonshire were accumulated, must have been 
 very similar to those which have long existed in the Riviera. 
 Sir Charles Lyell describes some remarkable deposits near 
 Nice ; l there torrents from the Alps bring down vast 
 quantities of detritus, fine in summer, coarse in winter, 
 and this is poured into the Mediterranean, and deposited 
 in slanting layers immediately outside the mouths of the 
 torrents, the shore being so steep that depths of 2,000 and 
 3,000 feet are found within half a mile of the beach. An 
 elevated delta of this kind can be studied in the valley of 
 the Magnan (near Nice), where inclined beds of sand, marl, 
 gravel, and conglomerate succeed one another in cliffs 200 
 to 600 feet high for a distance of nine miles ; if their in- 
 clination were assumed to be a dip, this would give a thick- 
 ness of many thousand feet, whereas their real thickness 
 cannot be proved to be even one thousand. 
 
 Similar accumulations are probably frequent where the 
 conditions are similar, and the aspect of the coarse sand- 
 stones of Teignmouth and Dawlish, with their angular 
 fragments of local rocks, seem to be torrential deposits of 
 this kind. The overlying marls may indicate submergence, 
 or a rise in the level of the water from increased rainfall, 
 which carried the coast-line farther west, and so allowed 
 a finer sediment to rest upon the coarse shore-beds. 
 
 Whether the northern areas were at this time lake- 
 basins, or low-lying terrestrial surfaces on to which mate- 
 rial was swept by mountain torrents, is very uncertain. 
 Professor Ramsay suggests a lacustrine origin for the 
 whole of the British Trias, but Professor Bonney remarks 2 
 that " the number and size of the pebbles (in the Bunter) 
 
 1 " Students' Elements of Geology," fourth edition, 1885, p. 20. 
 
 2 " Geol. Mag.," Dec. 2, vol. vii. p. 407. 
 
CHAP. VIII.] TBIASSIC PERIOD. 
 
 seem to point to the action of strong currents, such as would 
 only occur in an open sea or in the delta of a large river. 
 The average Staffordshire pebbles would require a current 
 of about three miles an hour to sweep them along. Larger 
 pebbles, up to six or eight inches in diameter, are by no 
 means infrequent.'* 
 
 If we adopt the lake theory, we must suppose two long, 
 narrow, and shallow sheets of water, each receiving the 
 current of a rapid river at its northern end. To account 
 for the character and limited extent of the Lower Bunter 
 Sandstone, we must conclude that the rivers were at first 
 only of sufficient volume and velocity to carry sand into the 
 lakes, and that their sandy deltas gradually filled up the 
 spaces which were then covered by water. The wider ex- 
 tension of the Pebble Beds would indicate a rise in the level 
 of the lake-waters due to an increased winter rainfall ; an 
 increase which might be caused by continued elevation of 
 the country. We must assume that the rivers then became 
 equal to transporting pebbles over the same areas, and 
 that a pebbly delta was superimposed upon the sandy one, 
 gradually extending beyond the tracts covered by the lower 
 sandstones, and round the southern termination of the 
 Pennine range. The upper sandstones, if deposited in water, 
 would indicate a decrease in the velocity of the streams, 
 and a return to the former conditions, except that no such 
 deposit was formed in the eastern tract. 
 
 This view of the manner in which the Bunter series was 
 laid down is not altogether satisfactory. Professor Bonney 
 says l he has always felt it difficult to explain the great 
 length of these Triassic tracts on the " filled-lake " theory, 
 and to account for the entire absence of mud or shale. He 
 thinks that the idea of subaerial river deltas, such as are 
 found in some parts of India, Persia, and Abyssinia, offers 
 a simpler explanation of some of the facts. On this theory, 
 
 1 Address to Geol. Sect, of Brit. Assoc., 1886, p. 18. 
 K 
 
130 NEOZOIC TIME. [CHAP. VIII. 
 
 the tracts now covered by the Bunter were flat lands on to 
 which the torrents from the surrounding hills swept the 
 detritus which they carried, at first dropping the pebbles in 
 the mountain valleys, and only carrying sand on to the 
 plains. 
 
 The final arrangement of this sand seems frequently to 
 have been accomplished by the wind (see p. 119), and we 
 may therefore suppose that during the greater part of the 
 year the plains formed bare and arid deserts, over which 
 hot winds whirled clouds of sand, and on which no living 
 creature could find sustenance. Such conditions would 
 account for the total absence of organic remains in the 
 Lower Triassic sandstones of Britain. When the period of 
 increased rainfall came on the torrents would carry the 
 pebbles to greater distances, and there may have been a 
 time when the streams were strong enough to sweep out all 
 the detritus which had accumulated in the upper valleys, 
 and to spread it over the lowlands in the shape of the 
 pebble beds. Depression and decreasing rainfall would 
 bring back the former conditions, and a partial recurrence 
 of sandy deposits. 
 
 That the mountain torrents should only fill their chan- 
 nels in the winter or rainy season is not at all improbable, 
 for this is the case with many watercourses in eastern 
 Egypt and Abyssinia at the present day. In those coun- 
 tries immense quantities of debris are swept out of the 
 hill-valleys by the heavy rains which occasionally occur in 
 winter time, and are spread out over the plains and wider 
 valleys which occur at lower levels, and which in the dry 
 season form arid tracts of sandy and pebbly desert. It is 
 probably to such regions that we must look for a type of 
 the conditions which prevailed in Britain during the earlier 
 part of the Triassic period. 
 
 When the depression which ushered in the conditions of 
 the Keuper epoch took place, an inland sea of considerable 
 
PLATE VI. GEOGRAPHY OF THE TRIASSIC PERIOD (KEUPER). 
 
CHAP. VIII.] TEIASSIC PERIOD. 131 
 
 size and very irregular shape was formed. We cannot say 
 exactly how this was, in the first instance, filled with water ; 
 it does not seem to have had any previous connection with 
 the open sea as the Dyassic lakes had, and as the modern 
 Caspian has had ; it was probably a freshwater lake, which 
 gradually became salt by the concentration of its waters, 
 like the Salt lakes of North America. It may be that the 
 outlet of the lake which previously existed in the south- 
 west of England was blocked by volcanic disturbances and 
 local upheaval, so that its waters gradually rose and over- 
 flowed the low barrier of Palaeozoic rocks which separated 
 them from the northern tracts. However this may be, it 
 is certain that in Upper Triassic times there was a large 
 space of water occupying the whole of central England, but 
 divided by the Pennine chain into two long gulfs or arms, 
 one of which spread to some distance east of Lincolnshire 
 and Yorkshire (see Plate VI.), and the other extended into 
 Cumberland and the north-east of Ireland. How much of 
 the Irish Sea was covered by this arm it is very difficult 
 to say, and the geography of this portion of the lake can 
 only at present be guessed at. 
 
 Southward a gulf extended across what is now the Eng- 
 lish Channel, and terminated in Normandy, but the course 
 of that part of the shore-line which ran below the east of 
 England is uncertain, because of the doubt existing with 
 regard to the age of the red rocks beneath London (see 
 p. 123), but the line on the map (Plate VL) is drawn in 
 accordance with the more probable view. 
 
 We may feel confident that there was still a large tract 
 of land on the east side of the lake, comparable in many 
 respects to that which lay to the westward ; we know that 
 it was composed of Carboniferous, Devonian, and Silurian 
 rocks similar to those of North Devon, Wales, and Shrop- 
 shire, and we may reasonably assume that it was a hilly 
 and rocky region such as Wales is now, and presented a 
 
132 NEOZOIC TIME. [CHAP. VIII. 
 
 similarly irregular coast-line. Both the eastern and western 
 land- tracts had long been exposed to the action of rain and 
 rivers, and were doubtless sculptured into a network of 
 ravines and valleys, which opened into wider valleys and 
 plains at lower levels. That one such valley opened east- 
 ward along the site of the British Channel is evident from 
 the manner in which the Keuper marls trend westward 
 into that channel ; this old valley in and south of Glamor- 
 ganshire lay probably along the course of the Carboniferous 
 Limestone, and led westward into the heart of the hilly 
 region which then united Pembroke and Devonshire, and 
 of which Lundy Island is the sole remaining fragment. 
 Another smaller inlet, penetrating into the centre of Devon- 
 shire, seems to be indicated by the strip of Trias which ex- 
 tends westward from Crediton, and doubtless there were 
 many other such inlets, bays, and estuaries, along the 
 shores of the great Triassic lake. 
 
 Such was the lake in which the sandstones, marls, salt 
 and gypsum beds of the Upper Trias were deposited. The 
 climate of the country was probably warm and dry, and 
 the saline waters of the lake were doubtless clear, and 
 probably of that deep blue tint which such waters generally 
 present. The ripple-marks, sun-cracks, and reptile-tracks 
 so frequent on the surface of the sandstones, show that 
 the volume of the lake- waters was subject to variations, 
 and that there were times when tracts of sand were exposed 
 and dried in the sun, and on these the strange reptiles of 
 the period have left their footmarks. It was also princi- 
 pally during such times of partial desiccation that the beds 
 of rock-salt and gypsum were deposited by precipitation 
 from the saline waters. 
 
 That at least one island existed in the lake is proved by 
 the relations of the Rhsetic and Liassic beds to the Dolo- 
 mitic conglomerate in the Mendip district, the newer beds 
 overlapping the conglomerate along the flanks of these hills, 
 
CHAP. VIII.] TRIASSIC PERIOD. 133 
 
 which were doubtless much steeper and higher then than 
 they are now. 
 
 It will be seen from the map (Plate VI.) that I have 
 supposed the Scottish Triassic deposits to lie on the sites of 
 two smaller and separate lacustrine areas. It might, of 
 course, be argued that the western basin was only an arm 
 of the Anglo-Hibernian lake, and that it was also connected 
 with the north-eastern basin by a narrow channel along the 
 site of the Great Glen ; but the absence of rock-salt and 
 gypsum in the Scotch Trias, and the presence of bivalve 
 shells resembling Cyrena at Ardtornish, are facts which 
 make it probable that the water of the Scotch lakes was 
 fresh, and not salt, and consequently that the connection 
 between them and the salt lake was by means of a river 
 channel. 
 
 The absence of the Ehaetic beds and the estuarine cha- 
 racter of the Lower Lias in Sutherland are also facts which 
 confirm the view that the Scotch lakes were at a somewhat 
 higher level than the great salt lake ; and the contrast be- 
 tween the marine and estuarine character of the Lower 
 Lias of the two districts seems to indicate that the level of 
 the eastern was higher than that of the western. Hence 
 we seem justified in concluding that in Triassic times the 
 eastern discharged itself into the western, and that the 
 overflow of the latter was conducted by a river into the 
 western arm of the great salt lake. "We may, in fact, re- 
 gard the Scotch lakes as the mountain-fed reservoirs of the 
 Anglo-Hibernian lake. 
 
CHAPTER IX. 
 
 JURASSIC PERIOD. 
 
 THE Jurassic strata, comprising the Lias and the Oolitic 
 series, succeed the Triassic marls with complete con- 
 formity, the passage from one system to the other being 
 through a group of grey marls, shales, and limestones, 
 which are known as the Rhsetic or Penarth Beds. The 
 Jurassic system is divisible into three rock groups or 
 series. 
 
 The Lower or Liassic series is essentially a clay forma- 
 tion, with occasional bands of lime stone, sand, and ironstone 
 of variable thickness. 
 
 The Middle Jurassic series consists mainly of limestones, 
 with only subordinate bands of sand and clay. 
 
 The Upper Jurassic, again, is an argillaceous series, the 
 limestones being discontinuous, and sometimes absent or 
 replaced by clays. 
 
 The most persistent formations are the three great clays : 
 the Lower Lias, the Oxford, and the Kimeridge Clays. 
 These range all across England, and form broad tracts of 
 low-lying land ; while the intermediate limestones, where 
 they are well developed, form long ridges, with escarp- 
 ments facing the west or north-west, in consequence of the 
 prevalent easterly dip. 
 
 1. Stratigraphical Evidence. 
 
 Ehcetic and Lias. The Ehaetic Beds, though in Britain 
 they are quite a subordinate division, are of special interest, 
 
CHAP. IX.] JURASSIC PERIOD. 135 
 
 because they mark the epoch when the great Triassic lake 
 was first invaded by the sea. At, or near the base of the 
 Ehaetic shales, there is usually a layer of shaly sandstone, 
 which contains phosphatic nodules and is crowded with the 
 remains of fish and small reptiles, and sometimes there are 
 several such layers. It would appear as if the sudden 
 irruption of the sea- water was prejudicial to the inhabi- 
 tants of the Triassic lake, so that most of them died, and 
 their bones, scales, and teeth were drifted into layers on 
 the sea-floor. 
 
 The Ehsetic Beds have been found everywhere in Eng- 
 land where the junction of the Trias and Lias is exposed, 
 and they occur in the north-east of Ireland, but are not 
 known in Scotland. It is true that on the western Scot- 
 tish coasts the base of the Lias is nowhere clearly exposed, 
 but Professor Judd thinks that no representative of the 
 Rhaetic shales exists there. These beds, therefore, so far 
 as our present knowledge enables us to judge, were con- 
 fined to the area of the Anglo-Hibernian lake. On the 
 borders of this area, as on the Mendip Hills and in Gla- 
 morganshire, the shales and limestones are sometimes re- 
 placed by sands and sandstones. 
 
 The Lias has a wider extension ; its thickness is often 
 more than 1,000 feet, and it must have overlapped the 
 Trias more or less in every direction, though the actual 
 extent of the Lower Lias may not have been very much 
 greater than that of the Trias, because the western coast of 
 the Triassic lake was in many places very steep. The 
 broad outcrop of the Lias stretches across England from 
 Dorset to Yorkshire, and outlying tracts occur in Stafford- 
 shire, Shropshire, and Cumberland, and in the north-east 
 of Ireland. They occur also on both sides of the Scottish 
 Highlands. 
 
 The thick clays and shales of this series indicate a sea 
 into which many rivers discharged a constant supply of 
 
136 NEOZOIC TIME. [CHAP. IX. 
 
 muddy material derived from the waste of the surround- 
 ing land. The shaly layers, which are familiar to us under 
 the name of Lias, are evidently such as were formed in the 
 more central and deeper parts of the sea, and there are 
 only a few localities where littoral beds of this age have 
 been preserved ; but of these it is desirable to give some 
 special account. 
 
 Shore-beds of Lower Liassic age are known in four dis- 
 tricts, viz., the Men dip district, Glamorganshire, the Inner 
 Hebrides, and eastern Sutherland. In the Mendip district, 
 near Shepton-Mallet, the ordinary clays and thin lime- 
 stones pass into massive white limestones, associated with 
 conglomerates composed of Carboniferous Limestone and 
 chert. Again, on the northern flank of the hills near 
 Chewton-Mendip, and Harptree, there is a compact cherty 
 deposit, containing Lower Lias fossils, and resting indiffe- 
 rently on Old Red Sandstone, Carboniferous Limestone, and 
 Dolomitic Conglomerate. 1 
 
 Similar deposits occur in Glamorganshire, near Bridgend, 
 Sutton, Brocastle, and Cowbridge, the basal beds being 
 hard, cherty, conglomeratic limestones, and passing up 
 into massive limestones full of fossils. The Sutton stone 
 is a soft white limestone, and in it corals are particularly 
 abundant. 
 
 In the west of Scotland the lower part of the Lias re- 
 sembles that of South Wales, consisting of hard limestones 
 alternating with calcareous and conglomeratic sandstones. 
 Above these are shelly limestones and shales. On the east 
 coast these beds are represented by estuarine deposits. 
 At the base are coarse sandstones and conglomerates, with 
 pebbles derived from the Lias, and these pass up into a 
 series of sandstones and shales, with thin layers of clay 
 and coal, the whole attaining a thickness of between 400 
 and 500 feet. 
 
 1 Woodward, " Geology of England," second edition, p. 265. 
 
CHAP. IX.] JURASSIC PERIOD. 137 
 
 It is rather remarkable that in three of these districts 
 the shore-beds should be chiefly limestones, and we must 
 infer that in these places, at least, very little detritus of any 
 kind was carried in from the land at the beginning of the 
 Liassic period. That this should be the case round the 
 Mendip island is quite natural, but that limestones should 
 be formed on the margin of the western inlet between 
 Wales and Devon requires explanation ; possibly this is to 
 be found in the supposition that freshwater lakes existed 
 in the country to the west, and that these for a time 
 arrested and detained the mechanical detritus brought 
 down by the rivers, leaving only the calcareous matter in 
 solution to be carried on to the sea by the effluent stream. 
 This, when added to the lime derived from the waste of 
 the Carboniferous Limestone along the shore, was more 
 than the sea-water could hold in solution, and the forma- 
 tion of limestones was the result. In the Scotch case, we 
 may suppose that the Sutherland basin was the lake or 
 lagoon which received the detritus, and thus allowed the 
 formation of limestones in the western gulf. 
 
 The only shore-beds of Middle Liassic age preserved to 
 us are those on the Scottish coast, where the Scalpa beds 
 of Professor Judd, 1 in the islands of Scalpa, Skye, and 
 Eaasay, consist of calcareous sandstones, 200 feet thick, 
 containing the fossils of the English Marlstone. In Mull 
 they are represented by soft greenish sandstone with few 
 fossils ; and similar beds seem to have been formed in the 
 eastern basin, blocks of them occurring in the Boulder 
 clays of Elgin and Moray. 
 
 No marginal deposits of Upper Liassic age are known, 
 but it may be noticed that round the Mendip Hills the 
 water was very shallow throughout the Liassic period, the 
 whole series being in some places represented by only 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxxir. p. 710. 
 
138 NEOZOIC TIME. [CHAP. IX. 
 
 30 feet of strata, in which beds of Lower, Middle, and 
 Upper Lias can be distinguished. This is the case near 
 Badstock, and it is quite possible that the Mendip ridge 
 then extended much further eastward than it does now. 
 
 In Gloucestershire the total thickness of the Lias is little 
 short of 1,000 feet, but at Burford in Oxfordshire it is only 
 650, the difference being due to the thinning of the Middle 
 and Upper members. The formation probably continues 
 to become thinner toward the east, but its limits in that 
 direction are not yet known. 
 
 Middle Jurassic Series. Between the Upper Lias clays 
 and the limestones of the Inferior Oolite there are in the 
 south-west of England certain sands which are grouped by 
 some with the Lias and by others with the Oolite, but they 
 are, in fact, passage beds from one series to the other. 
 Above them come a variable series of limestones and marls, 
 the former generally oolitic, and containing an abundance 
 of fossils. These beds are divided into two groups the 
 Inferior Oolite and the Great Oolite and in the south-west 
 of England they are entirely of marine origin. 
 
 In Dorsetshire their combined thickness is over 700 feet, 
 but they thin northward toward the Mendips, and near 
 Erome they are not more than 100 feet thick. Here the 
 Inferior Oolite overlaps the Lias, and rests on the older 
 rocks, its base being sometimes conglomeratic. 
 
 North of the Mendips they thicken again, and reach a 
 total of 460 feet near Cheltenham; but when followed 
 eastward, they are found to thin very rapidly, the whole of 
 the Inferior Oolite being represented in the valley of the 
 Cherwell by 10 or 12 feet of brown sandstone, and the 
 Great Oolites above are not more than 150 feet thick. 
 There is at the same time evidence of the vicinity of land in 
 this direction, not only from the sandy character of the In- 
 ferior Oolite, but from a thin zone of estuarine beds at the 
 base of the Great Oolite. These are known as the Stones- 
 
CHAP. IX.] JURASSIC PERIOD. 139 
 
 field Beds, and contain the remains of many plants and 
 terrestrial animals. 
 
 In the continuation of the series to the north-east these 
 estuarine beds thicken at the expense of the Great Oolite 
 limestones, while other beds of a similar character replace 
 part of the Inferior Oolite. Moreover, in Northampton, 
 the two estuarine groups are separated by a plane of 
 erosion or unconformity, and the whole series is in some 
 places reduced to less than 100 feet, of which only 30 feet 
 are marine limestones. 
 
 In Lincolnshire there is a greater thickness of marine 
 limestones, a lenticular mass of limestone coming in 
 between the two estuarine groups, but this becomes very 
 thin in the north of that county, and in Yorkshire the 
 estuarine beds thicken, so that they eventually form a thick 
 series of deposits in which marine limestones are quite 
 subordinate features. As this Yorkshire series is such a 
 contrast to that of the south-western counties, a brief 
 account of its component members may be given. 
 
 At the base of the section are marine sandstones and 
 ironstones (about 50 feet thick). Above these is a group 
 of estuarine sandstones and shales, with much carbona- 
 ceous matter and thin seams of impure coal ; this group is 
 280 feet thick near Whitby, but thinner to the westward. 
 Then comes a band of calcareous sandstone, which contains 
 marine fossils, and appears to be the attenuated represen- 
 tative of the Lincolnshire Limestone; but above this is 
 another mass of estuarine deposits, from 50 to 100 feet 
 thick, containing several workable seams of coal. This 
 group is succeeded by the Scarborough Limestone, a len- 
 ticular mass, which is thin on the coast, but thickens to the 
 west and north-west. Above this limestone is a third set 
 of estuarine shales and sandstones, from 120 to 220 feet 
 thick, which are generally supposed to represent the Great 
 Oolite, as they are covered by the Cornbrash, and there is 
 
140 NEOZOIC TIME. [CHAP. IX. 
 
 no other bed containing the marine fossils of the Great 
 Oolite except the Cornbrash. Thus, out of a total thick- 
 ness of about 650 feet, no less than 550 are estuarine beds 
 a fact which proves the Yorkshire basin to have been in 
 close proximity to land of a continental character, and to 
 have received the deposits of a large river, the mouth of 
 which lay apparently to the north-east of the Yorkshire 
 coast. 
 
 Of the western extension of the Middle Jurassic strata 
 we have absolutely no evidence beyond the fact that all the 
 marine limestones thicken in that direction a fact which 
 may be held to prove that their present outcrops are far 
 removed from their original western limits ; and since the 
 series seems to have overlapped the Lias in other direc- 
 tions, we may assume that it did also to the west. Eegard- 
 ing their eastern extension, important evidence has recently 
 been obtained from a boring at Eichmond, in which sandy 
 clays and limestones with Great Oolite fossils (87 feet 
 thick) were found below the Cretaceous strata, and resting 
 directly on red (Devonian ?) rocks. At Meux's brewery in 
 London similar beds occurred in the same position, the 
 rocks below being undoubtedly Devonian. It is clear, 
 therefore, that between Oxford and Eichmond the Great 
 Oolite overlaps the Inferior Oolite and the whole of the 
 Liassic series, so as to lie directly on the surface of the old 
 rocks which formed the eastern land of the period. 
 
 These Oolites have not been proved to exist beneath any of 
 the south-eastern counties, but as they have a wide distri- 
 bution over northern and central France, there can be little 
 doubt that they are continuous beneath the Channel and 
 the southern part of England. 
 
 The northern extension of this series is proved by thick 
 deposits along the western coasts of Scotland, where the 
 succession of marine and estuarine beds is very instructive. 
 In Skye and Eaasay the Inferior Oolite is represented by 
 
CHAP. IX.] JURASSIC PERIOD. 141 
 
 shales, sandstones, and limestones of marine origin, and 
 380 feet thick, but including 60 feet of white sandstone, 
 with bands of shale containing plant remains. But of the 
 Great Oolite there is no marine representative, its place 
 being taken by a remarkable formation which is evidently 
 part of the delta of a large river ; the mass of this consists 
 of grey and white sandstones often current-bedded and 
 ripple-marked, but both above and below these are groups 
 of black shale and limestones, in which freshwater shells 
 are abundant, together with the remains of reptiles, turtles,, 
 and fish. Professor Judd remarks upon the striking re- 
 semblance which these beds present to the Purbeck series of 
 Dorset. Similar beds occur on the east coast of Sutherland, 
 where the highest member of the series is a coal-seam 
 3f feet thick, resting on black shales with plants and 
 crushed freshwater shells. From these facts it is clear that 
 at this epoch the Scottish gulf was entirely silted up, and 
 converted into swampy land, like that composing the delta 
 of any large modern river. 
 
 Upper Jurassic Series. Like the Lias this is essentially 
 an argillaceous series, but it includes large lenticular and 
 episodal developments of limestone and calcareous sand. 
 The succession is most complete in the south of England, 
 where it consists of the following members in descending 
 order : 
 
 5. Purbeck beds, estuarine and freshwater. 
 
 4. Portland limestone and sands. 
 
 3. Kimeridge clay. 
 
 2. Corallian limestone and sands. 
 
 1. Oxford clay. 
 
 The Oxford Clay is generally more or less sandy at its. 
 base, but the mass of the formation consists of dark grey 
 or blue clay with layers of calcareous nodules. In the south 
 of England it is from 300 to 600 feet thick, and it main- 
 tains the same character and average thickness to the north 
 
142 NEOZOIC TIME. [CHAP. IX. 
 
 of Lincolnshire, but then becomes thinner, and in York- 
 shire it is only from 100 to 150 feet thick, the lower part 
 (30 to 80 feet) consisting of sandstones and sandy lime- 
 stones (Kellaways Eock). 
 
 The beds known as Coral Eag and Calcareous Grit are a 
 variable set of oolitic and coralline limestones and calca- 
 reous sandstones, which are only developed in the southern 
 counties and in Yorkshire, being absent, or represented by 
 clays with thin layers of limestone, in the counties of 
 Bucks, Beds, Hunts, Cambridge, and Lincoln. At Upware 
 near Ely, however, there are the remains of a small isolated 
 coral-reef, part of the mass consisting of coral-rock, and 
 part of soft coral- sand limestone. 
 
 The Kimeridge Clay consists of dark clays and carbona- 
 ceous shales, which are continuous across England. Theyare 
 thickest in the southern counties, 700 to 800 feet in Dorset, 
 and over 1,000 in the sub-Wealden boring (Sussex). To- 
 ward the Midland counties they become thinner, being only 
 500 at Swindon, and apparently not more than 100 feet at 
 Headington, near Oxford. Northward, however, they 
 thicken again, but cannot be estimated, because of the 
 overlap of the Cretaceous rocks. In Lincolnshire the group 
 is at least 500 feet thick, and is about the same at Speeton 
 in Yorkshire. 
 
 The Portland Beds of Dorset consist in the lower part of 
 calcareous sands and marls (about 80 feet), and in the 
 upper of shelly, chalky, and oolitic limestones (80 to 90 
 feet). A similar succession is found in the Vale of War- 
 dour, but at Swindon the limestones are partly replaced by 
 sands, with large calcareous concretions, and are separated 
 into two stages by a surface of erosion, the uppermost beds 
 being partly marine and partly freshwater, with a Purbeck 
 facies. 1 The lower sands and marls are still 76 feet thick, 
 
 1 See J. F. Blake in " Quart. Journ. Geol. Soc.," vol. xxxvi. p. 203 , 
 and " Historical Gteology," Bohn's Series, p. 348. 
 
CHAP. IX.] JURASSIC PERIOD. 143 
 
 but it is clear from this remarkable section that the upper 
 beds here were formed in much shallower water, and that 
 the area was rapidly converted into an estuary, or fresh- 
 water lake. When next seen in Oxford and Bucks other 
 changes are found to take place ; the lower sands thin out 
 gradually from 70 feet at Shotover to 6 near Aylesbury, 
 and the upper beds consist of limestone and fine silty sand 
 in alternate layers (25 feet), passing up into a set of marly 
 shales and limestones of freshwater origin (15 feet) ; these 
 last, though homotaxially the equivalents of the Purbeck 
 beds, are probably, in reality, of Upper Portland age. Beds 
 of this character occur within a few miles of Leighton 
 Buzzard, and may originally have stretched a little further 
 north-east, as Portlandian fossils occur in the Cretaceous 
 sands of Bedfordshire; but no Portlandian strata are 
 again found till we reach Yorkshire, where black shales of 
 this age overlie the Kimeridge Clay at Speeton. 
 
 As regards their south-eastern extension, sands and sand- 
 stone (about 80 feet thick) occurred at this horizon in the 
 Sussex boring, and they are found in the north of France, 
 so that they are doubtless continuous beneath the Channel, 
 but they do not appear at the western outcrop of the series 
 in Normandy. 
 
 Before noticing the Purbeck Beds we may glance at the 
 correlatives of the marine Upper Jurassic series in Scotland. 
 On the west coast the Oxford Clay only is seen, but in 
 Sutherland a more complete series is found : the Oxford Clay 
 is over 300 feet thick, and is marine throughout ; it is suc- 
 ceeded by a zone of white cherty sandstone, with the fossils 
 of the Lower Calcareous Grit overlain by a mass of estua- 
 rine sandstones with layers of lignite ; these are 400 feet 
 thick, and are surmounted by marine beds with Coral Eag 
 fossils. The Kimeridge Clay is also represented by a thick 
 and variable series of beds, chiefly estuarine sandstones in 
 the lower part, with marine shales and limestones (500 feet 
 
144 NEOZOIC TIME. [CHAP. IX. 
 
 thick) in the upper part, the highest "beds being light- 
 coloured sandstones without any fossils. Near the Ord of 
 Caithness thick beds of breccia occur amongst the shales of 
 the Kimeridge Clay, and their formation is explained by 
 Professor Judd as follows : 1 " The alternation of the 
 brecciated beds with the finely laminated and quietly de- 
 posited strata and the confused arrangement of the blocks 
 in the former, their admixture with trunks of trees, stems 
 of cycads, and other plant remains, seem to indicate that 
 the quiet deposition of the semi-estuarine beds was inter- 
 rupted by the occasional occurrence, in the rivers just 
 alluded to, of floods of the most violent character. These 
 appear to have swept angular masses, just separated from 
 their parent rock by frosts or landslips, subangular masses 
 which had lain for a time in the course of the streams, and 
 the rounded pebbles of the river-beds, along with trunks of 
 trees torn from their banks, all in wild confusion out to sea, 
 where they were mingled with the sea-derived materials of 
 the shell-banks and shoals." 
 
 The Purbeck Beds exist only in the south of England ; 
 they consist of limestones, shales, marls, and black earths 
 in thin layers, which exhibit alternations of terrestrial, 
 freshwater, and marine conditions. Near Swanage, in 
 Dorset, they are 400 feet thick, but they thin rapidly both 
 to the west and north. In the Vale of Wardour only the 
 lower and middle portions remain, and these are only 70 
 feet thick as compared with 300 feet at Swanage ; at this 
 rate of thinning they would not extend more than ten or 
 twelve miles farther north beneath the Cretaceous rocks, 
 but there is great uncertainty with regard to their northern 
 limit. The freshwater beds of Swindon have been called 
 Purbeck, but it is very doubtful whether these were ever 
 actually continuous with those of the Yale of Wardour. 
 
 1 "Quart. Journ. Geol. Soc.," vol. xxix. p. 195. 
 
CHAP. IX.] JURASSIC PERIOD. 145 
 
 True Purbecks occur in Sussex near Battle, where their 
 thickness is estimated at 400 feet, so that we may suppose 
 them to be continuous from Dorset eastward through 
 Hants and Sussex, but they probably die out in Kent, and 
 are not known in the north of France. 
 
 In the Lower Purbecks of Dorset dirt-beds or carbona- 
 ceous soils are a conspicuous feature, and the presence of 
 rooted stumps of cycadean and coniferous trees proves 
 them to be actually terrestrial surfaces. At the base of the 
 Middle Purbecks is a carbonaceous shale from which twenty- 
 four species of small marsupial mammals, together with 
 the bones of several crocodiles and lizards have been ob- 
 tained. It has been pointed out by Professor E. Forbes l 
 and Mr. C. J. A. Meyer, 2 that the changes from freshwater 
 to marine deposits are abrupt, and that there is no real 
 intermingling of marine and freshwater fossils in the same 
 stratum, but a gradual return from brackish to freshwater 
 conditions ; these facts seeming to indicate lacustrine areas 
 which were subject to occasional and sudden inroads of the 
 sea, and, therefore, in all probability, lakes or lagoons in 
 a silted-up bay or gulf. There is little evidence of direct 
 fluviatile action ; drift wood or plant remains are rarely 
 found except in direct connection with terrestrial surfaces. 
 One of the limestones, containing freshwater shells and 
 nodules of chert, resembles those of the Tertiary lacustrine 
 strata of central France. Lastly, the limestones of the 
 Upper Purbecks being chiefly composed of the shells of the 
 freshwater mollusc Paludina, are such as would be formed 
 in quiet lacustrine waters. 
 
 The Purbecks of Sussex are a much less variable group, 
 and were apparently formed in somewhat deeper water ; 
 they do not include any dirt-beds, but consist chiefly of 
 shales, with two groups of hard grey thin-bedded lime- 
 
 1 "Brit. Assoc. Rep.," Sect. C. } 1850. 
 
 2 " Quart. Journ. Geol. Soc.," vol. xxviii. p. 245. 
 
 L 
 
146 NEOZOIC TIME. [CHAP. IX. 
 
 stones. Paludince are rare, and the principal fossils are 
 
 freshwater bivalves and cyprids in the shales; marine 
 shells are still less frequent. 
 
 2. Physical History and Geography. 
 
 1. Lower Jurassic Time. The physical geography of 
 the Ehaetic and Liassic epochs was a simple and direct 
 modification of that which prevailed during the preceding 
 Triassic period. No local elevations and subsidences took 
 place in the British area, for the Ehsetic and Liassic beds 
 occupy the same basins of deposit as those which hold the 
 Keuper marls ; the great lakes or inland seas in which the 
 latter were accumulated became by submergence the seas 
 and bays in which the shales and limestones of the Lias 
 were laid down. 
 
 This submergence set in doubtless toward the end of the 
 Triassic period, and affected the whole of the Triassic north- 
 European continent ; the epoch of the Avicula contorta 
 zone marks the time when the depression had proceeded so 
 far as to submerge the lowest tract of land which lay 
 between the great salt lakes and the wide-spreading southern 
 ocean. It is very probable that at this time the level of 
 the water in the salt lakes had been greatly reduced by 
 evaporation, and was perhaps several hundred feet below 
 that of the sea outside, and that when the dividing barrier 
 was submerged, the sea waters would rapidly invade the 
 lake basins and fill them up to a common level. 
 
 Let us consider the nearly parallel case of the Caspian 
 Sea at the present day; the level of this sea is 85 feet 
 below that of the Black Sea, and it is surrounded by exten- 
 sive low-lying areas which were formerly covered by its 
 waters before the sea shrank to its present dimensions ; if 
 therefore the waters of the Black Sea were admitted to the 
 Caspian through the depression of the present barriers, 
 
CHAP. IX.] JURASSIC PERIOD. 147 
 
 they would quickly spread over a large area in Central Asia 
 which is now for the most part a dry and sandy desert. I 
 do not mean to infer that anything like a cataclysmal in- 
 flux of water would take place; the first inroad would 
 doubtless occur during the prevalence of a strong west 
 wind, 1 and would be only a temporary invasion, but as 
 submergence went on, such invasions would be of frequent 
 occurrence, till at length a permanent connection was 
 established. 
 
 Two important results would follow from such a change : 
 
 (1) large numbers of the creatures living in the Caspian 
 would be immediately killed unless they could support the 
 changed conditions of water and food ; if destroyed, their 
 remains would doubtless be laid out, and stratified, as it 
 were, on the bottom of the sea, thus forming bone-beds. 
 
 (2) The climate and appearance of the surrounding country 
 would be gradually altered ; evaporation from the newly- 
 created sea would give rise to the formation of clouds ; these 
 would fall again as rain on the neighbouring hills ; rills and 
 rivers would come into existence, and the ordinary processes 
 would be set in action ; the country would be irrigated and 
 fertilized, and the products of erosion would be washed 
 into the widening sea. A scene of death and decay, desert 
 wastes and slowly shrinking lakes would be converted into 
 a sea full of active creatures, bordered by a region where 
 the plash of waters and the hum of insects were unceasing 
 sounds. 
 
 Such must have been the change which ensued when the 
 Bhaetic waters filled the basins of the Triassic lakes. The 
 bone-beds testify to the suddenness of the invasion and the 
 inability of the Triassic fish and reptiles to survive the 
 change. 
 
 The fauna of the succeeding shales and limestones suggests 
 
 1 If there were tides in the Black Sea, it would occur when there was 
 an unusually high tide. 
 
148 NEOZOIC TIME. [CHAP. IX. 
 
 the inference that the mixture of sea and salt-lake water 
 was not at first favourable to molluscan life ; the assem- 
 blage of species is a small one, and consists almost entirely 
 of bivalves, their shells having that dwarfed appearance 
 which is generally the case with those living in unfavour- 
 able habitats. No Cephalopoda, Gasteropoda, Brachiopoda, 
 Echinoderms, or Corals occur, but all these come in with 
 the Lower Lias, proving that the waters were at first 
 shallow and unfit to support these creatures, but that 
 further submergence opened up free communication with 
 the outside sea, bringing in a greater depth of water, and 
 all the conditions favourable to the increase of molluscan 
 life. The Liassic sea, indeed, with its large and active 
 reptiles, its numerous fishes, and other inhabitants, must 
 have presented a great contrast to the heavy and nearly 
 lifeless waters of the salt Triassic lakes. 
 
 The plants and insects of the Rhsetic and Lias also testify 
 to the alteration of the climate, the humidity of the air, 
 and the general fertility of the surrounding region. It is 
 remarkable, however, that the insects are chiefly of a 
 small size, and not such as might be expected to occur in 
 association with the semi-tropical assemblage of marine 
 creatures, but are rather such as would inhabit temperate 
 climes at the present day. On this point Sir A. Ramsay 
 has some interesting remarks. During the Triassic and 
 Liassic periods, he says, it is not improbable to suppose 
 that the mountains of Wales were at least double their 
 present height, and were, therefore, 5,000 to 6,000 feet 
 high, so that if a tropical or warm temperate fauna existed 
 along the coast, a cold temperate land-fauna might exist 
 among the hills. Now Professor Edward Forbes, while 
 dredging along the coast of Lycia (Asia Minor), " observed 
 that during the rainy season, the surface of the water was 
 often partially covered with quantities of dead insects, 
 washed into the sea from the neighbouring land. By far 
 
CHAP. IX.] JURASSIC PERIOD. 149 
 
 the greater number of these insects were not derived from 
 the hot low-coast territories, but were borne to the sea from 
 the more distant and lofty mountain lands (7,000 to 10,000 
 feet high), by sudden floods which are then of frequent 
 occurrence." They also, in accordance with the elevated 
 regions from whence they came, bore the characters of 
 temperate and cold climates ; and Sir A. Ramsay thinks it 
 probable " that the insect remains described by Mr. Brodie 
 were washed from the mountain country we have described 
 into the surrounding seas, and there entombed amid crea- 
 tures of a tropical character." ] 
 
 The geography of the British region, so far as concerned 
 the relative positions of land and water, was similar to that 
 of the Triassic period. The waters of the Liassic sea 
 covered the whole area of the Triassic lake, and extended 
 some little way beyond its margins. From the southerly 
 extension of the Lias through France it would seem that 
 the southern sea gained access to the British area through 
 that country, and if this were so we can understand how 
 the Jurassic fauna and flora came to have their semi- 
 tropical character. With continental land extending far 
 to the east and%est through the northern temperate zone, 
 but not reaching far into the Arctic Circle, 2 and with an 
 open sea spreading from tropical climes to its southern 
 shores, we have exactly the conditions which would carry 
 a high temperature and tropical productions far into the 
 temperate zone. 
 
 As to the western shore of the British sea we can only 
 say that it lay considerably to the westward of the present 
 boundary of the Trias, though probably not far beyond 
 
 1 " Mem. Geol. Survey," vol. i. p. 325. 
 
 2 There are Jurassic deposits in East Greenland, Spitzbergen, Northern 
 and Eastern Russia, and the fossils they contain make it improbable 
 that there was any accumulation of ice round the North Pole at this 
 time. 
 
150 NEOZOIC TIME. [CHAP. IX. 
 
 the original limits of the latter ; that on the sites of the 
 English and Bristol Channels there were gulfs which 
 narrowed westward, and that the Mendip Hills seem to 
 have formed an island, parts of which remained above the 
 level of the sea throughout the whole epoch, whence we 
 may conclude that the slopes of the hills were then very 
 steep, and that their higher parts rose to a height of 800 
 or 900 feet above the level of the Rhaetic waters. 
 
 From Swansea Bay the coast probably ran through 
 Glamorgan and Monmouth to the Malvern Hills, and 
 thence trended north-westward through Shropshire and 
 Denbighshire, and across the Irish sea to the west coast of 
 Ireland. As to the space now occupied by the Irish 
 Channel no evidence is forthcoming, but if a gulf then 
 existed on its site, it probably opened northward, and 
 narrowed southward. From Ireland the sea extended over 
 the site of the western Scottish lake, and thence probably 
 up the great glen to the north-eastern basin ; here the 
 estuarine beds of the Lower Lias mark the debouchure of 
 a large river, but the overlying marine beds show that as 
 the submergence proceeded the sea gained on the land, 
 while the sandy beds of the Middle Liasr prove that the 
 narrow water spaces were soon silted up. 
 
 With regard to the eastern limits of the Liassic sea we 
 know that it encroached considerably upon the eastern 
 land, for near Northampton, where the Trias is only from 
 50 to 100 feet thick, the Lias is over 700 feet, and this 
 thickness must carry it some 30 or 40 miles further east, 
 unless the slope of the eastern land became very steep. 
 Further south it probably thins out beneath the Chiltern 
 Hills (see fig. 3), and thence we may suppose that its 
 boundary curves round to the south-east below Berkshire, 
 Surrey, and Sussex, and crossing the English Channel 
 enters France a little to the north of Abbeville. 1 North - 
 
 1 De Lapparent, " Trait4 de la Geologie," second edition, p. 912. 
 
PLATE VII. GEOGRAPHY OF THE LIAS AND INFERIOR OOLITE. 
 
CHAP. IX.] JURASSIC PEEIOD. 151 
 
 eastward there was a broad gulf over the eastern arm of 
 the Trias sic lake, but there is no reason to suppose that 
 the land connecting Scotland and Scandinavia was sub- 
 merged at this time. 
 
 The view of Liassic geography above given differs from 
 what has been previously suggested l in the restriction of 
 the north-eastern part of the sea, and in connecting the 
 Sutherland basin with the western gulf instead of with the 
 eastern. Professor Hull in his restoration of Jurassic 
 geography 2 has depicted an extension of the sea round the 
 east of Scotland and entering the Sutherland basin from the 
 east, but he informs me that this map is intended to repre- 
 sent the epoch of the Oxford Clay, and, as we have no actual 
 evidence for any such continuous extension either of the 
 Keuper or the Lias, we can only consider the probabilities 
 which are suggested by the characters of the beds above and 
 below the Lias. Now there is nothing in the British Trias 
 to show that it was ever connected with that of Germany, and 
 I have adopted the view that even the Keuper was formed in 
 a restricted basin bordered on the east by a continuous 
 barrier of high ground (see Plate VI.), which rose from 
 beneath the eastern lip of the Northumberland coalfield, 
 just as the Pennine Range does from its western lip. If 
 this were so, then it is not likely that the Liassic sea en- 
 croached farther on to the land in a north-easterly direction 
 than it did eastward beneath England. Again, if we con- 
 sider the strata which overlie the Lias, we find estuarine 
 conditions prevailing in Yorkshire (see p. 139), and proving 
 the vicinity of land to the east and north-east at that time ; 
 hence it- is not likely that the land lay very much farther 
 off during the formation of the underlying Lias. 
 
 The deposition of so great a thickness of dark-coloured 
 clay and shale in Liassic times is another point that calls 
 
 1 " Historical Geology," p. 359. 
 
 2 " Physical History of the British Isles," pL x. 
 
152 NEOZOIC TIME. [CHAP. IX. 
 
 for explanation, and it may be fairly assumed that this 
 material was mainly supplied by the destruction of the 
 Coal-measure shales. Large tracts of Coal-measures must 
 have existed at this time both in Ireland and Scotland, and 
 the rivers flowing off these tracts would pour little else 
 than black mud into the surrounding sea, while the waves 
 would eat deep into such portions as came within their 
 reach during the gradual submergence. 
 
 Middle Jurassic Time. The change from Liassic shales 
 to Oolitic limestones and marls is a rapid one, and is ac- 
 companied by a great change in the fauna, for though 
 many Liassic species range into the passage beds (Midford 
 Sands), yet very few survived till the era of the Inferior 
 Oolite. These facts imply that a considerable and rapid 
 change took place in the physical conditions of the period, 
 but what this change was is not quite so easy to determine. 
 At first sight nothing seems easier to explain than such a 
 change ; a clay succeeded by a limestone seems to point to 
 a general depression, whereby the extent of the sea was 
 enlarged, and its depth increased ; but it is an error to 
 suppose that all limestones are deep-water formations, 1 and 
 oolitic limestones in particular are generally of shallow-water 
 origin. Moreover, the Stonesfield Beds, with their proofs of 
 shallow water and the vicinity of land, occur in the middle 
 of this Oolitic series, the whole of which becomes more and 
 more estuarine in its character as it is followed to the north- 
 east. These facts prove conclusively that the water was not 
 on the whole so deep as it had been in Liassic times. Lastly, 
 in Oxfordshire the Upper Lias and Inferior Oolite seem to 
 thin out beneath the Great Oolite, and there are also signs 
 of erosion between the Inferior Oolite and the Lias ; these 
 facts imply an elevation of the sea-floor and not subsidence, 
 for in the latter case the Inferior Oolite would overlap the 
 Lias. 
 
 1 See " Physical Geology," Part L, ch. xii. 
 
CHAP. IX.] JURASSIC PERIOD. 153 
 
 It by no means follows, however, that this elevation was 
 uniform and equable over the whole area. We notice, in 
 fact, a decided tendency to the formation of separate basins 
 of deposition, and to the upheaval of certain submarine 
 ridges having a general east and west direction across 
 England. Thus we can hardly understand the continuance 
 of shallow water over the Mendip district without suppos- 
 ing a local upheaval, and it is not unlikely that there is an 
 eastward extension of this axis in the form of a ridge sepa- 
 rating the southern basin from that of Gloucestershire. 
 A second ridge stretched across North Oxfordshire and 
 Northampton, the evidence given on p. 138 proving that 
 over these counties there was a broad space of shallow 
 water separating the deeper basin of the Cotteswold area 
 from the equally deep north-eastern basin. 
 
 This ridging up of the Liassic sea-floor, and the conse- 
 quent formation of three separate submarine basins like 
 jthose which exist in the modern Mediterranean, must have 
 produced very material changes in the physical conditions 
 of the Jurassic sea, and was probably one reason why the 
 waters of the southern basins became so rapidly clear 
 enough for the growth of reef-building corals ; the muddy 
 material would be all thrown down in the northern basins, 
 that of Yorkshire on the one hand and of the Irish sea on 
 the other, the submarine ridge preventing the currents from 
 carrying much of it over the central and southern counties. 
 
 It is clear, however, that this was not the only cause for 
 the cessation of the shaly and muddy sediment, and it is 
 probable that the supply of such sediment was diminished 
 by a slight elevation of the country from which it was 
 obtained. Assuming that the supply was chiefly derived 
 from the erosion of the Coal-measure shales (as previously 
 suggested), it is certain that the amount of such material 
 carried off a given area by one system of rivers must have 
 become less and less as the rivers cut their way through 
 
154 NEOZOIC TIME. [CHAP. IX. 
 
 the Coal-measures into the sandstones, limestones, and older 
 rocks beneath ; a slight elevation would quicken this process 
 of erosion, and the natural result would be that the rivers 
 would carry less mud, but more sand in suspension, and 
 more calcareous matter in solution. In the combined effect 
 of the two causes above indicated we seem to have a com- 
 plete explanation of the rapid change from the physical 
 conditions of the Lias to those of the Oolitic sea. 
 
 In the epoch of the Great Oolite there appears to have 
 been a certain amount of subsidence in the southern dis- 
 tricts, for we know that this stage overlapped the Lias in 
 the latitude of London (see p. 140), and also in the north- 
 east of France ; this overlap may, however, have been partly 
 due to erosion of the coast by the waves ; there is no proof 
 that the northern area was affected by the subsidence, and 
 it was evidently insufficient to cause any material altera- 
 tion of the geographical conditions. 
 
 Throughout this Oolitic epoch the clear water and warm 
 temperature of the southern sea were favourable to the 
 growth of coral-reefs, and it is well known that the Oolitic 
 limestones are to a large extent formed from the materials 
 derived from the waste of such reefs and from the shells of 
 the marine creatures which swarmed in their neighbour- 
 hood. As in similar situations at the present time, Echi- 
 noderms, Brachiopoda, Pelecypoda, and Gasteropoda were 
 especially abundant. 
 
 The fauna and flora of the land were in keeping with 
 those of the sea. Terns, Cycads, and Equisetums abounded 
 on the borders of the rivers, and were mingled with Coni- 
 ferous trees on the higher slopes ; huge Dinosaurian Rep- 
 tiles, that walked or hopped on their hind legs like kanga- 
 roos, and small insectivorous Marsupials were the chief 
 vertebrate inhabitants of the dry land, but Crocodiles 
 swarmed in the rivers, and bat-like Pterodactyles flitted 
 through the air. 
 
CHAP. IX.] JURASSIC PERIOD. 155 
 
 The nearest approach in modern times to such a scene 
 as Britain must have displayed in the Middle Jurassic 
 period is to be found in Australia and its neighbouring 
 islands. There many of the Jurassic types still survive. 
 The indigenous Mammalia are all Marsupials ; the plants 
 include Ferns, Cycads, and Araucarian pines. Coral-reefs 
 fringe the shore, and in the waters are Cestraciont Fish, 
 and many of the same Molluscan genera as are found in 
 the Oolites, viz., Phasianella, Stomatia, Trigonia, Corbis, 
 and Terebratula, with others that have a wider distribution. 
 There are, however, no survivors of the Jurassic Reptiles, 
 or of the Ammonites and Belemnites which swarmed in 
 the older seas. 
 
 Upper Jurassic Time. During this part of the Jurassic 
 period a considerable subsidence took place, and this was 
 followed by a still greater and more continued upheaval, 
 which eventually raised the greater portion of the British 
 area into dry land, and brought the Jurassic period to a, 
 close. 
 
 Once more we have a complete change in the character 
 of the sediment, and as the phenomena exhibited are exactly 
 in reverse order to those of the change from Lias to Oolites, 
 we may assume that they were caused by movements of 
 precisely an opposite kind, and that the epoch of the Oxford 
 Clay was produced by a general and equable subsidence of 
 the whole region from the very south of England to the 
 extreme north of Scotland. 
 
 In this case the sands and sand-rock of the Kellaways 
 Beds are the strata formed at the commencement of the 
 change, and constitute the zone of passage. The sandy 
 nature of the Kellaways rock precludes us from supposing 
 it to have been a deep-water deposit, but its fauna indicates 
 that deep water was not far off, for in these beds a large 
 number of new Ammonites suddenly make their appearance, 
 and most of them continue in the Oxford clav. If further 
 
156 NEOZOIC TIME. [CHAP. IX. 
 
 testimony to the shallowness of the Great Oolite waters 
 were needed, the scarcity of Ammonites in the rocks of 
 that group would supply it, only three species being known 
 to occur in the Forest Marble and Cornbrash. The change 
 from Cornbrash to Kellaways is particularly striking in 
 Yorkshire, where the latter contains no fewer than forty- 
 one species of Ammonites, and only one is common to the 
 two deposits ; twenty of these species pass up into the 
 Oxford clay. Mr. Hudleston, who has made such a careful 
 study of the Yorkshire Oolites, 1 remarks : " Probably this 
 great sandbank was deposited during a submergence of 
 this region far more continuous in time and extended in 
 space than those more partial depressions which during 
 the period of the Lower Oolites (Middle Jurassic) had in 
 this region intercalated the spoils of the sea with those of 
 the estuary and the marsh. This more continuous descent 
 seems at length to have removed or lowered barriers which 
 had hitherto kept out the waters of a sea swarming with 
 strange Cephalopoda." 
 
 One of these barriers was undoubtedly that tract or pro- 
 montory of land which occupied the North Sea, and stretched 
 from Belgium into the eastern part of the British area 
 throughout the Liassic and Middle Jurassic periods. The 
 southern part of this ridge began to be submerged during 
 the formation of the Great Oolite, and though the Oxford 
 clay is not found beneath London, it occurs below Chatham 
 in Kent, and its absence further north is doubtless due to 
 the great denudation which took place in Cretaceous times. 
 We may therefore assume that a large part of the eastern 
 land was completely submerged during the formation of 
 the Oxford clay, and that by the close of this epoch a con- 
 tinuous deposit of the clay was spread over the whole of 
 the eastern and midland portion of the British area, and 
 
 1 " Proc. Geol. Assoc.," vols. iv. and v., and " Quart. Journ. Geol. 
 Soc.," vol. xxxiii. p. 272. 
 
CHAP. IX.] JURASSIC PERIOD. 157 
 
 that even the Scottish coast-lines were carried back so far 
 that the same clay was spread over areas where only estua- 
 rine deposits had previously been laid down (see p. 143) ; 
 but whether there was continuous sea outside the east of 
 Scotland, as Professor Hull thinks, is quite uncertain. 
 In this great deposit of dark blue clay we seem to have a 
 repetition of Liassic conditions, and it is highly probable 
 that the source of supply was the same namely, the Coal- 
 measures which once covered so large a portion of Wales, 
 Ireland, and North Britain. 
 
 The episode of the Corallian Beds marks a time when 
 from some cause the deposition of mud ceased over certain 
 parts of the sea-bottom, and the water became clear enough 
 for the growth of coral-reefs with their accompaniments of 
 calcareous sands, marls, and oolitic limestones. This episode 
 may have been caused either by the temporary diversion 
 of the mud-bearing currents, or by the diminution of the 
 supply, in the manner already explained when treating of 
 the change from Lias to Oolites. The latter is, perhaps, 
 the most probable cause, and we may regard the Corallian 
 stage as indicating a pause in the movement of subsidence 
 during which less muddy material was carried down by the 
 rivers. The succession of beds in Sutherland lends some 
 confirmation to this view ; there as elsewhere the Oxf ordian 
 clays and shales tell of submergence, but the overlying 
 sandstones (see p. 143) show that the currents were able 
 to carry sand further out from the shore, and over the deep 
 sea mud, as they might do if the land was stationary for 
 a time, and just as an extension of sand over mud is be- 
 lieved to be now taking place in the English Channel. 1 
 In the succeeding series of alternating marine and estuarine 
 beds we trace the progress of a further subsidence. It 
 would appear, therefore, that the intercalation of white 
 sandstones in the shallow waters of the Scottish area, and 
 1 See Godwin-Austen, " Quart. Journ. Geol. Soc.," rol. Ti. p. 82. 
 
 
158 NEOZOIC TIME. [CHAP. IX. 
 
 of corallian limestones in the deeper water of the English 
 sea, were due to one and the same cause. 
 
 During the formation of the Kimeridge Clay the subsi- 
 dence reached its farthest extent, and eventually a reverse 
 movement set in, the supply of mud grew scantier, and 
 the bluish argillaceous sands which underlie the Portland 
 stone were doubtless formed during upheaval. Finally, a 
 large part of the sea-bottom was raised into dry land, and 
 the sea was contracted into two separate branches or gulfs, 
 the separation of which seems to have resulted from the 
 upheaval of a tract across the centre of England a tract 
 which had formed a submarine ridge ever since the time 
 of the Lias. The existence of this ridge was mentioned on 
 p. 139, and the influence it had on deposition can be seen 
 from the following table of thicknesses, which shows that 
 the amount of sediment laid down over it was about 1,000 
 feet less than the accumulation in the basin to the south, 
 and 450 feet less than that in the area to the northward : 
 
 Wiltshire. Oxford and Lincolnshire. 
 
 Bucks. 
 
 Portland Beds . .. 100 ... 50 . . absent? 
 
 Kimeridge Clay .. 500 ... 150 ... 500 
 
 Corallian .... 200 . . absent . . absent. 
 
 Oxford Clay ... 500 ... 300 ... 350 
 Lower Oolites . 350 .. 100 . 200 
 
 Feet 1,650 600 1,050 
 
 This central tract now became an isthmus, uniting the 
 eastern and western Palaeozoic areas to one another, and 
 probably also to the southern end of the Pennine chain. 
 The emergence of this isthmus began in Portland times, the 
 sea of the Portland Limestone lying wholly to the south of 
 the latitude of Bedford, and opening southward through 
 France, while a northern gulf extending from Germany 
 reached into Yorkshire and Lincolnshire (see Plate VIII.). 
 
CHAP. IX.] JURASSIC PERIOD. 159 
 
 Once more, therefore, we find limestone in the south of 
 England and shale in the north, and in this case it is clear 
 that the formation of limestone was possible because of the 
 intervening barrier which prevented the influx of the 
 northern mud-bearing currents. 
 
 We have now brought the history of the British Jurassic 
 sea to a close, and have arrived at the epoch of the great 
 Purbeck-Wealden continent ; but before we can with any 
 confidence restore the physical geography of the Purbeck 
 and Wealden times, we must pause to ask what systems of 
 river-drainage would be likely to come into existence under 
 the circumstances of the Portlandian upheaval. In the 
 first place, the uprise of the central barrier which caused 
 the restriction of the north-eastern part of the Jurassic sea, 
 must have similarly affected the north-western branch of 
 the sea, and if we consider that this had probably been a 
 land-locked gulf throughout the Jurassic period, we are in- 
 evitably led to conclude that the Portlandian upheaval 
 must have converted it into a large inland lake. 
 
 In the absence of any Jurassic deposits of later date than 
 the Oxford Clay over this area there is, of course, no posi- 
 tive evidence for the existence of such a lake, but the pro- 
 bability of its having existed may be increased by another 
 process of inductive reasoning. If there were no such 
 catchment basin on the site of the gulf, this must have 
 formed a wide valley traversed by a river which would 
 receive many large tributaries from the mountains on 
 either side, and, flowing southward across what is now the 
 Irish Sea, would necessarily be a very large and powerful 
 stream, carrying down a great quantity of detritus. If it 
 continued its course over the newly-emerged bed of the 
 Jurassic sea in spite of the local upheaval across England, 1 
 
 1 There is no reason to suppose that the Irish Channel was then in 
 existence any more than the English Channel was, nor is it probable 
 that there was any opening westward into the Atlantic. 
 
 
160 NEOZOIC TIME. [CHAP. IX, 
 
 it must have emptied itself into one of the two marine 
 gulfs, and must have formed a great delta, so that we 
 should have expected the occurrence of a thick mass of 
 estuarine Portland-Purbeck deposits either in one basin or 
 the other, but there is no sign of such a formation ever 
 having existed in either. 
 
 K , however, a large lake existed on the site of the Irish 
 Sea, as indicated in Plate VIII., the detritus brought down 
 by the mountain streams would find a resting place, and 
 the excurrent river would be as clear as the Rhone when 
 it leaves the Lake of Geneva. Such a river, flowing 
 southwards and not receiving any important affluents, 
 might enter the southern gulf without giving rise to 
 any extensive estuarine or deltaic deposits, or leaving 
 any larger record of its existence than such a channel 
 and break in the marine sequence as is found at Swindon. 
 The Swindon section seems to indicate the presence of 
 a river of some size, and if the north-western river did 
 have the course above suggested this may have been its 
 debouchure. 
 
 Besides this river the only other streams, so far as we 
 can see, that could enter the southern or Purbeck basin 
 would be those draining the country to the west and south. 
 Now in Portland times the influence of these rivers does 
 not seem to have been great, and possibly they then carried 
 more material in solution than in mechanical suspension. 
 Even the subsequently-formed Purbeck beds of Dorset 
 are less fluviatile than lacustrine in character, and Mr. 
 Meyer has indeed argued for their purely lacustrine origin. 
 He goes so far as to speak of the Purbeck basin being 
 " probably from its commencement rather that of a lake, a 
 series of lagoons, or even of an inland sea, than of an 
 estuary in the ordinary meaning of the word." ! This. 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxviii. p. 245. 
 
PLATE VIII. GEOGRAPHY OF THE PORTLANDIAN EPOCH. 
 The lake and river system are hypothetical. 
 

 CHAP. IX.] JURASSIC PERIOD. 161 
 
 perhaps is pushing the inference too far, and the conditions 
 of the Purbeck basin seem to me more correctly described 
 as those of a silted-up gulf or bay, portions of which be- 
 came freshwater lakes or meres, such as formerly existed 
 in the Fenland of Norfolk and Cambridge. It is true that 
 the conditions of sedimentation in the Purbeck bay were 
 evidently different from those in the great bay of the Fen- 
 land ; the latter has been filled up chiefly by tidal silt, and 
 the areas of freshwater deposits are very small, while in 
 the former the lacustrine areas were large, and silt-bearing 
 currents were absent, so that even the marine deposits 
 were calcareous. Still, there is much analogy between the 
 cases, and I therefore agree with the wording of Mr. 
 Meyer's conclusion that it was " by the co-existence within 
 a comparatively wide area of a fauna suited respectively 
 to freshwater and brackish-water conditions, and by the 
 interchange of such conditions over portions of the same 
 area, supplemented by the occasional intrusion of the 
 ocean, that I would account for the alternation of fresh- 
 water, marine, and brackish-water fossils in the Purbeck 
 strata ; for neither the conditions of their accumulation 
 nor the life-conditions of their fauna appear to be suffi- 
 ciently in accordance with an estuarine position " (loc. cit., 
 p. 246). 
 
 On this view, too, the stratigraphical relations of the so- 
 called Purbeck beds of Oxford and Bucks admit of easy 
 explanation ; for if our view of Portlandian geography is 
 correct, it is exactly in this Midland district where we 
 should expect to meet with evidence of the early prevalence 
 of such conditions, and to find freshwater strata of an 
 earlier date than that of the Dorsetshire Purbecks. There 
 we find beds with Portlandian fossils passing up into 
 purely lacustrine strata, which were evidently deposited 
 in the quiet waters of a lake that was never invaded by 
 strong currents either of fresh or salt water. We may 
 
 M 
 
162 NEOZOIC TIME. [CHAP. IX. 
 
 conclude, therefore, that it was a large lake or mere which 
 occupied an area of newly-emerged and low-lying ground, 
 and that its level was maintained by the local rainfall, not 
 by the influx of a large river. 
 
 My attention has been directed to an essay by Professor 
 Hebert, 1 in which he discusses the physical history of the 
 Jurassic period in France. He divides it into two portions 
 a period of depression and a period of upheaval. He 
 considers that the former only lasted till the time of the 
 Great Oolite, and that the Jurassic sea then attained its 
 greatest superficial extension. Instead of admitting a fur- 
 ther submergence at the time of the Oxford Clay, he attri- 
 butes its absence over the exposed Great Oolite area to 
 non-deposition, and thinks the Oxfordian sea was limited 
 to the Parisian gulf, the sea-space becoming smaller and 
 smaller during succeeding epochs, till it was finally upraised 
 in Purbeck times. 
 
 To most English geologists this must seem a very crude 
 and antiquated view, but I am surprised to find that Pro- 
 fessor Gosselet and other French geologists hold similar 
 opinions, and interpret the geologial record of other systems 
 on the same principles. (See Gosselet's " Esquisse Geol. 
 du Nord de la France.") 
 
 1 " Les Mers Anciennes et leur Kivages dans le Bassin de Paris. 
 Part I. Terrain Jurassique." 1857. 
 
CHAPTER X. 
 
 THE CRETACEOUS PERIOD. 
 
 IN the south of England, where the highest Jurassic beds 
 are fully developed, there is a complete sequence 
 through the freshwater Purbeck and Wealden groups to 
 marine deposits of Cretaceous age ; but elsewhere through- 
 out Britain and the north of France the marine deposits of 
 the two systems are separated by a marked break and un- 
 conformity, representing the interval during which the 
 older rocks were upheaved and remained in the condition 
 of dry land. 
 
 In the south of France this gap is filled by a complete 
 series of marine deposits, which are known as the Neocomien 
 and Urgonien groups, and these, therefore, are the marine 
 equivalents of our Wealden series. In Yorkshire and 
 Lincolnshire also the freshwater series is partially repre- 
 sented by marine deposits, some of which are probably as 
 old as the upper part of the French and Swiss Neocomian, 
 but there is still an unconformity at their base. The 
 following is a tabular view of the members of the Creta- 
 ceous system in the south and north of England respec- 
 tively, with the names of their French equivalents ; the two 
 lower stages of the English succession being grouped as the 
 Lower Cretaceous series, and the four upper constituting 
 the Upper Cretaceous series. 
 
 
164 
 
 NEOZOIC TIME. 
 
 [CHAP. x. 
 
 Isle of Wight. 
 6. Tipper Chalk. 
 5. Middle Chalk. 
 4. Lower Chalk. 
 3. Upper Greensand ) 
 
 and G-ault. j 
 
 2. Lower Greensand, I 
 
 or Vectian. / 
 
 1. Wealden. 
 
 Yorkshire. 
 
 Upper Chalk. 
 Middle Chalk. 
 Lower Chalk. 
 
 Eed Chalk. 
 
 Speeton Clay, ) 
 . j 
 
 France. 
 Senonien. 
 Turonien. 
 Cenomanien. 
 
 Albien. 
 Aptien. 
 
 upper 270 feet. 
 
 Speeton Clay, \ Urgonien. 
 
 lower 230 feet, j Neocomien. 
 
 1. Stratigraphical Evidence. 
 
 Lower Cretaceous. The Wealden Beds are restricted to 
 a comparatively small area in the south of England, and 
 do not extend far beyond the limits of the Purbeck Beds. 
 They occupy the country known as the Weald of Kent and 
 Sussex, and pass beneath the chalk hills which surround 
 this district, but they do not extend far to the north, for 
 the deep borings at Chatham, Erith, and Eichmond proved 
 their absence at those places. Eastward they reach below 
 the Straits of Dover into the Boulonnais, and westward 
 they spread beneath Hampshire and the Isle of Wight into 
 Dorsetshire, but have not been traced beyond Osmington 
 and Bidgeway. Southward they do not seem to have 
 reached so far as the present shores of France, for they 
 do not appear below the Aptien at the northern end of the 
 Pay du Bray inlier in Normandy. 
 
 The Wealden Beds consist of thick lenticular alternations 
 of sand and clay, the sands being thickest in the lower part 
 and the clays in the upper part, so that they are usually 
 divided into (1) the Hastings Sand, and (2) the Weald 
 Clay. In the lowest beds (Ashdown Sand) layers of lignite 
 are not unfrequent ; the Wadhurst clay also contains lig- 
 nite as well as nodules of clay ironstone. In the sands 
 

 CHAP. X.] CRETACEOUS PERIOD. 165 
 
 near Cuckfield and Lindfield there are thin layers of con- 
 glomerate, the pebbles in which are largely derived from 
 Palaeozoic rocks, and were probably brought down by 
 streams draining off the land to the north ; and this is in- 
 teresting as showing that streams had already cut down 
 through the Upper Jurassic clays to the Palaeozoic rocks of 
 that region. The Weald Clay consists of clays and shales 
 with local beds of sandstone and many layers of shelly 
 limestone, the latter consisting of Paludina shells, and re- 
 sembling the Upper Purbeck limestones. 
 
 The Wealden Beds are about 1,800 feet thick in the west 
 of Sussex, and they attain a still greater thickness near 
 Swanage in Dorset ; but when followed westward they are 
 found to thin out rapidly, being only 172 feet thick in Man- 
 of-War Cove. In Dorset, moreover, the series is not divi- 
 sible into a lower sandy and an upper clayey portion, the 
 sands and clays alternating throughout, but the highest 
 beds are always shales with limestone bands. 
 
 The fossils of the Wealden are entirely freshwater and 
 terrestrial, plant remains, minute Crustacea, freshwater 
 mollusca, fish and reptile bones occurring throughout ; and 
 there is no admixture of marine species, except at the very 
 top of the series in the Isle of Wight. 
 
 Wealden Beds occur in the Vale of Wardour, but are 
 not seen again in Wiltshire. In Oxfordshire there are 
 some freshwater deposits overlying the so-called Purbeck 
 Beds, but there is a decided unconformity between them, 
 and just as the one group in all probability antedated the 
 true Purbeck Beds, so it is thought that the newer group 
 is of posterior date to the true Wealden series. 
 
 In Yorkshire and Lincolnshire there are contemporary 
 beds of marine origin. In Yorkshire these are blue clays 
 with a basement bed containing rolled fossils derived from 
 Jurassic rocks ; in Lincolnshire they are partly clays and 
 partly sandstones, with a similar nodule-bed at the base ; 
 
166 NEOZOIC TIME. [CHAP. X. 
 
 and in Norfolk there are clays and soft sands which may 
 be of the same age ; but how far they may originally have 
 extended southwards we do not know. 
 
 The Vectian 1 group is most completely and clearly ex- 
 posed in the Isle of Wight, where it is divisible into three 
 portions : (1) Atherfield Beds, 150 feet, chiefly clays ; (2) 
 Walpen Sands, 400 feet ; (3) Shanklin Sands, 256 feet. 
 They are entirely marine, and the deposits of a shallow sea, 
 rather deep and muddy at first, but becoming shallower 
 afterwards. The basement bed of the Atherfield Clay is a 
 seam of coarse grit containing small pebbles, with the teeth 
 and bones of fishes ; of this Mr. Meyer remarks, " it is just 
 such an accumulation of sediment as would result from the 
 dispersion of shore deposits over the floor of a moderately 
 deep lake. The fish-bones are those possibly of inhabitants 
 of the Wealden waters, and their presence at the junction 
 of the two formations may be due to the suddenness of 
 their destruction by the change from fresh to salt water." : 
 
 The Atherfield Clay is the deposit of a deepish gulf or 
 estuary, but the Walpen Sands are current -formed beds in 
 shallower water, and this fluviatile action is very evident 
 
 1 Vectian. This group is usually known as the Lower Greensand, 
 although it has long been admitted that this is an awkward and incon- 
 venient appellation. So long ago as 1827 Fitton protested against its 
 use ; in 1845 he suggested the name Vectine in its stead, and in 1885 I 
 proposed that of Vectian, which is only Fitton's term in another form. 
 The fact that Phillips applied this name to the Upper Eocene Tertiaries 
 cannot be held as any objection, for Fitton has undoubtedly a prior 
 claim to it, and since the Fluviomarine series is now known as the 
 Oligocene, no one is likely to revive Phillips' use of Vectian. The term 
 Upper Greensand is equally indefensible, for the beds so designated are 
 not a separate group, and should be united with the Gault under a new 
 name. In the following pages I shall use the name Vectian for all 
 strata that are equivalent to the beds between the Wealden and the 
 Gault, such as the upper part of the Speeton Clay, which no one likes 
 to call Lower Greensand, and which it is incorrect to call Neocomian. 
 
 2 " Quart. Journ. Geol. Soc.," vol. xxviii. p. 248. 
 
CHAP. X.] CRETACEOUS PERIOD. 167 
 
 at Pimfield on the Dorset coast, where the beds include 
 layers of lignite and shales with Cyrena. In this direction, 
 too, the whole group thins out rapidly, and is not more 
 than 100 feet thick at Worbarrow Bay. 
 
 The Yectian beds seem, indeed, to have their maximum 
 thickness (800 feet) below Hampshire, for at the west end 
 of the Wealden area, near G-odalming and Petersfield, the 
 whole group is not more than 450 feet thick, and it con- 
 tinues to diminish eastward, being about 320 feet at Seven- 
 oaks, 250 at Sandgate and Folkestone, and only 31 be- 
 neath Dover. The same diminution can be traced along 
 the foot of the South Downs, its thickness at Eastbourne 
 being only 70 feet, and in each case it is the highest beds 
 which remain ; the same is the case at Chatham, where a 
 boring has proved 41 feet of the upper sands resting on 
 Oxford Clay. 
 
 It is clear, therefore, that the Vectian beds of the Weald 
 thin to north-east, east, and south-east ; that they should 
 thin east and north-east is not surprising, for we know 
 that land lay in that direction, but that they thin to the 
 south-east is important as showing that the water was 
 shallow near Eastbourne, and therefore that part of the 
 southern shore-line was probably not far off that place. 
 
 How far the Atherfield Clay and Walpen Sands extend 
 through the north of Hampshire has not yet been ascer- 
 tained, but they probably thin out northward and westward 
 in the same way as they do northward and eastward in 
 Kent, for when the Vectian emerges from beneath the 
 G-ault in Wiltshire only the representative of the Shanklin 
 Sands remains. In Wilts and Berks this upper member 
 consists of brown ferruginous sands, with occasional, beds 
 of conglomerate, which contain a curious mixture of pebbles 
 rounded pebbles of quartz, banded slate, and cherty lime- 
 stone, similar to those which occur in the Portland Beds, 
 and which may have been derived from the destruction of 
 
168 NEOZOIC TIME. [CHAP. X. 
 
 these beds, as the rest of the pebbles have come from the 
 neighbouring Jurassic rocks, namely, the Coral Rag and 
 Kimeridge Clay. It does not seem likely that the pebbles 
 of Palaeozoic rocks were derived directly from such rocks, 
 because the localities are so far distant from any outcrops 
 of Palaeozoic rock that are likely to have been exposed at 
 that time, unless they came from a buried continuation of 
 the Mendip range ; neither is it easy to see how they can 
 have been derived from the Trias, for the strata containing 
 them are shore-beds formed in close proximity to the 
 actual land margin. 
 
 These pebble beds extend as far as Baldon, south of 
 Oxford, but near G-arsington and Shotover a very different 
 set of beds come in, the characters of which more resemble 
 those of the Walpen Sands at Punfield ; they consist of 
 variously coloured sands and clays, with beds of iron-ochre 
 and fuller's earth, and they contain freshwater shells 
 (Gyrena, Unio, and Paludina), with pieces of coniferous 
 wood. These beds extend in outliers by Brill and Quain- 
 ton to Whitchurch ; and south of this line, near Thame 
 and Hartwell, there are other beds in which marine fossils 
 have been found. The actual relations of these two sets of 
 beds have not yet been ascertained, but it may be remarked 
 that no intercalation of beds with marine and freshwater 
 fossils has yet been observed, and that the marine beds are 
 generally in close proximity to the Grault. It is possible, 
 therefore, that the freshwater beds are lacustrine and 
 lagoon deposits of a slightly earlier date, and were formed 
 in a low-lying tract of land which was afterwards invaded 
 by the sea. This supposition finds some confirmation in 
 Professor Morris's observation, that at the base of the 
 marine sands near Hartwell there are derived blocks of 
 brown sandstone containing freshwater fossils. 1 
 
 1 See " Geol. Mag.," vol. iv. p. 458. 
 
CHAP. X.] CRETACEOUS PERIOD. 169 
 
 The Upper Vectian sands next appear near Leighton and 
 Woburn, where they are 200 feet thick, and consist chiefly 
 of yellow and white sands, but have near the base a re- 
 markable seam of phosphate nodules, with fossils and 
 pebbles derived chiefly from Upper Jurassic strata ; there 
 are pebbles of quartz and chert like those of the Berkshire 
 beds, as well as fragments of an older Cretaceous rock. 
 The sands above are current-bedded, and the inclination 
 of the layers is generally south or south-eastward, showing 
 that the prevalent currents came from the north. Similar 
 beds with layers of nodules stretch through Bedford and 
 Cambridge as far as Ely. 
 
 With regard to the subterranean extension of these 
 sands, it is known that they do not stretch far to the east- 
 ward. In Cambridgeshire they are present at Shelford 
 and Sawston, but appear to be absent at Saffron Walden in 
 the north of Essex. 1 In Hertfordshire they occur below 
 Hitchin, but are absent at Cheshunt and Ware. At Eich- 
 mond there are ten feet of calcareous sandstone, with a 
 pebble bed at its base, which consists of material derived 
 from Palaeozoic and Jurassic rocks; this is probably of 
 Vectian age, but no such beds occur under London. It is 
 clear, therefore, that the sands thin out against the slope 
 of the Palaeozoic rocks which underlie the east of England, 
 see fig. 3, p. 115. 
 
 In Norfolk other beds begin to set in, the descending 
 succession being (3) ferruginous sandstone or Carstone, (2) 
 blue clay, (1) soft yellow and white sand. In Lincolnshire 
 the clay is thicker, and in Yorkshire the whole is repre- 
 sented by clays, which rest on still older Cretaceous clays 
 (see p. 164). The Lower Vectian consists of clays with 
 Pecten cinctus and Meyeria ornata (120 feet), and the Upper 
 
 1 A boring here was carried through blue clays below the Chalk for 
 about 550 feet without any record of sand, and without finding any 
 water. (See " Mem. Geol. Survey," Expl. Sheet 47, p. 79.) 
 
170 NEOZOIC TIME. [CHAP. X. 
 
 of blue and black clays (150 feet). These were formed in 
 much deeper water, and include representatives of the 
 lowest Vectian beds, as well as the higher, many of the 
 fossils being similar to those found in the Atherfield Clay. 
 The Yorkshire succession, however, has much more re- 
 semblance to that of Hanover than to that of southern 
 England or France, and there can be little doubt but that 
 they were formed in a Germanic sea or gulf, which con- 
 stituted a separate marine province. 
 
 Upper Cretaceous. The lowest stage of this series con- 
 sists of a variable group of clays, marls, sands, and sili- 
 ceous rocks which are known as the G-ault and Upper 
 G-reensand. It used to be thought that the argillaceous de- 
 posits were always older than the arenaceous, but it is pro- 
 bable that they are to a large extent replacive and coeval. 
 
 As a matter of fact, in East Kent the formation consists 
 entirely of clay, more or less marly at the top, and including 
 a thin bed of dark glauconitic sand. To the westward 
 other beds of sand and siliceous stone come in, and in the 
 Isle of Wight it is lithologically divisible into three por- 
 tions, the lowest being blue clay (100 feet), the central 
 consisting of sandy micaceous marl (55 feet), and the upper 
 of yellow and grey sands, with layers of cherty stone (100 
 feet). Still further west the clays entirely disappear, being 
 probably overlapped by the higher beds, which consist of 
 grey and yellow sands, argillaceous below and glauconitic 
 near the top, with a total thickness of 150 to 130 feet. 
 These form the mass of the Blackdown Hills, and cap the 
 Trias of Haldon Hill south of Exeter. 
 
 A similar group of beds doubtless swept northwards 
 across the centre of England, but only the eastern part re- 
 mains, all the western part between the Welsh hills and 
 the Cretaceous escarpment having been removed by the 
 erosion of subsequent periods ; we cannot, therefore, trace 
 the passage from G-ault to G-reensand across the Midland 
 
CHAP. X.] CRETACEOUS PERIOD. 171 
 
 counties, but the oblique section along the line of the out- 
 crop reveals a still more remarkable lithological change. 
 The Gault in the south of Bedfordshire consists of clay 
 and micaceous marl, and is about 230 feet thick; thence to 
 the north-east it gradually diminishes in thickness, the 
 whole formation at Stoke Ferry in Norfolk being only 
 60 feet thick, and consisting of marly clay. Farther north, 
 at Roydon, it is only 20 feet, and includes layers of chalky 
 limestone and of red marl. At Dersingham there is only 
 
 7 feet of grey, yellow, and red marl, and this appears to 
 pass into the red limestone of Hunstanton. 1 
 
 In Lincolnshire and South Yorkshire there is a similar 
 red rock at the base of the Chalk, but as it is followed 
 through Yorkshire considerable changes take place ; at 
 the north-west extremity of the Wolds it is very thin, but 
 is still an essentially calcareous rock ; to the east and 
 north-east it thickens rapidly, becoming at the same time 
 much more argillaceous, till at Speeton it is 30 feet thick, 
 and Mr. W. Hill informs me that the material of the lower 
 
 8 or 10 feet contains nearly equal quantities of insoluble 
 siliceous matter and carbonate of lime. 
 
 The clays of the Lower G-ault seem to have been de- 
 posited in a shallow sea of 50 to 70 fathoms deep, which is 
 about the depth of the sea between England and Ireland, 
 while the fossils of the Upper Gault indicate a depth of 
 100 fathoms and upward. 2 The Gault and Greensand of 
 the Isle of Wight and the Midland counties was probably 
 all deposited in a sea of less than 100 fathoms, and the 
 depth of the water became less toward the west, where the 
 deposits exhibit abundant evidence of current action and 
 the vicinity of land. In the sands of Haldon Hill Dr. 
 Sorby found that only a proportion of one-tenth of the 
 
 1 See " Quart. Journ. Geol. Soc.," vol. xliii. p. 550 et seq. 
 
 2 See Price on the "Depth of the Gault Sea^ Proc. Geol. Assoc.,"" 
 vol. ir. p. 269. 
 
172 NEOZOIC TIME. [CHAP. X. 
 
 quartz grains were well rounded and worn, while in those 
 of the Isle of Wight the proportion is probably greater. 
 
 The G-ault of Norfolk is a deposit formed in deeper 
 water than that of Folkestone, and has a greater resem- 
 blance to the Chalk Marl than to the G-ault clays of the 
 southern counties ; that it was formed at a distance from 
 any land whence detritus was carried seaward is proved 
 by the microscopical investigations of Mr. W. Hill. He 
 has shown that the amount of inorganic matter, such 
 as recognizable particles of quartz felspar and mica, de- 
 creases as the gault is traced northward, while in the 
 Norfolk marls the proportion of organic material (Forami- 
 nifera and shell fragments) becomes very large ; and it is 
 doubtless to this gradual elimination of the transported 
 sediment, and the consequent concentration of the calca- 
 reous matter, that the thinning out of the Gault is due. 1 
 
 Just as the upward succession at Folkestone, from the 
 blue pyritous clay of the Lower Gault to the grey marly 
 clays of the Upper Gault, indicates the deepening of the 
 sea in which they were deposited, so the lateral passage 
 from the argillaceous Gault of Bedford and Cambridge to 
 the marls and limestones of West Norfolk points to an 
 increasing depth of water and distance from land. 
 
 Borings in the east of England prove that the Gault 
 underlies the whole of it, and rests on the surface of 
 Palaeozoic rock which was left uncovered by the Veetian 
 Sands. It thins, however, to the north and north-east, and 
 at Holkham in Norfolk there is only 10 feet of clay over- 
 lain by 8 feet of red marly chalk, a section which may be 
 compared with that of Eoydon. 
 
 Nothing comparable to the Gault occurs either in Ireland 
 or Scotland, the basement bed being a glauconitic sand 
 containing Pecten asper and Ammonites varians, fossils 
 
 1 Quart Journ. Geol. Soc.," vol. xliii. p. 580. 
 
CHAP. X.] CRETACEOUS PERIOD. 173 
 
 which only occur together in the Chloritic Marl and in the 
 sands just beneath it in Dorset. We may conclude, there- 
 fore, that the sea did not reach Ireland till this horizon 
 was reached, and it is possible that the Irish Pecten asper 
 zone is really the time equivalent of part of our Chalk 
 Marl, the fauna of this zone being a shore-fauna which 
 advanced as the shore receded. Consequently it may have 
 prevailed at a western locality after the sediments contain- 
 ing it to the eastward had been covered by a considerable 
 depth of the succeeding Chalk Marl. 
 
 In this connection the Cenomanien deposits of Sarthe in 
 Brittany are instructive, for here the Chalk Marl (Craie de 
 Rouen) passes westward into a sandstone containing some 
 of the same fossils, but mixed with a shallow- water fauna 
 which includes Pecten asper. 1 
 
 From the G-reensand to the Chalk Marl of England the 
 transition is always rapid and sometimes sudden. There 
 is evidence of strong current action at this epoch, conse- 
 quent probably on the submergence of certain barriers, 
 and these currents seem to have swept away portions of 
 the deposits which then formed the sea-bottom, sifting the 
 soft marls and sands, washing out such fossils as were 
 hardened by the deposition of phosphate of lime, and in- 
 corporating them in the basement bed of the new forma- 
 tion. This bed is generally known as the Chloritic Marl, 
 and it frequently lies on a plane of contemporaneous 
 erosion. In the south of England it contains fossils 
 derived from the Pecten asper zone, but in Bedford and 
 Cambridge the derived fossils have been obtained from 
 the G-ault, and the bed is sometimes called the Cambridge 
 G-reensand. 
 
 The Cambridge G-reensand has also yielded a number of 
 rock-fragments which have evidently been brought from 
 
 1 A. Guillier, Geologie de la Sarthe," PaJis, 1886, p. 213. 
 
174 NEOZOIC TIME. [CHAP. X. 
 
 distant sources. These include blocks of granite, hyperite, 
 basalt, porphyrite, and felsite, with fragments of hard 
 Palaeozoic rocks and of quartzite schists and gneiss. Some 
 of them resemble Scotch and Norwegian rocks, but are 
 just as likely to have come from the north of Ireland. 
 From their number and general angularity it is believed 
 that these fragments were transported by floating ice 
 in the same way as similar blocks are now carried south- 
 ward by floating icebergs, and dropped on to the bottom 
 of the Atlantic at the present day. Their presence may at 
 any rate be regarded as indicating the influx of cold cur- 
 rents from more northern shores. 
 
 The Chalk Marl is an impure chalk, containing in the 
 southern counties from 16 to 24 per cent, of fine sand and 
 silt, with small particles of glauconite. It was formed in 
 deeper water than the G-ault, and attains its greatest thick- 
 ness in and east of Berkshire, thinning both to the north 
 and to the south-west ; but as in the case of the Grault, the 
 thinning to the south-west is accompanied by an increase 
 in the proportion and size of the quartz grains, while 
 toward the north-east there is a diminution in the number 
 of recognizable quartz particles and of other inorganic 
 materials, with an increase of minute shell-fragments, and 
 of other calcareous materials. 1 
 
 The outcrop of the Chalk Marl along the base of the 
 main escarpment from Dorset to Norfolk presents us with 
 a transverse section of a large lenticular mass of slowly 
 accumulated material, having its maximum thickness over 
 a tract which lay at some distance from the land, and yet 
 was not beyond the reach of currents bearing a certain 
 amount of finely-divided inorganic detritus, and from this 
 region of maximum development we can trace it into the 
 purely calcareous deposit of a deeper sea on the one hand, 
 
 1 See W. Hill in " Quart. Journ. Geol. Soc.," vol. xliii. p. 582. 
 
CHAP. X.] CRETACEOUS PERIOD. 175 
 
 and into shallow-water beds, with a minimum of calcareous 
 matter, on the other. 
 
 The Totternhoe Stone seems to indicate a temporary 
 increase in the strength of the prevalent currents, enabling 
 them to carry coarser particles to a greater distance. This 
 bed attains its maximum thickness in the counties of 
 Bedford and Cambridge, thinning out to the north and 
 south. 
 
 Upward through the Lower Chalk there is the same 
 transition to a more purely calcareous deposit that we 
 found taking place horizontally in the case of the Chalk 
 Marl. Deposition was now more uniform, the thickness 
 of the beds above the Totternhoe Stone varying less than 
 those below. At the summit of the Lower Chalk, how- 
 ever, there is evidence of another physical change in the 
 occurrence of one or two layers of grey shaly marl. This 
 horizon is continuous from the Isle of Wight to Suffolk ; it 
 is obscure in Norfolk, but occurs again throughout Lin- 
 colnshire and Yorkshire. There is nothing more remark- 
 able in the stratigraphy of the Chalk than the wide 
 extension of these shaly marls, but they contain little 
 that throws light on the circumstances which led to their 
 formation. 
 
 We might suppose that the shale was due to elevation 
 of the sea-floor and a consequent shallowing of the water, 
 but if this were so we should expect the incoming of a 
 shallow- water fauna, whereas the fauna of the marls is a 
 very small assemblage, and is similar to that of the Chalk 
 below. It seems more probable that the sea was at this 
 time invaded by a flow of cold water from the north in a 
 broad and steady current, which was strong enough to 
 prevent the deposition of much chalky matter, but too far 
 from land to carry much sediment with it. This hypo- 
 thesis of a northern under-current will also account for the 
 sudden disappearance of the creatures which lived in the 
 
176 NEOZOIC TIME. [CHAP. X. 
 
 Lower Chalk sea. They may have been driven away by 
 the coldness of the water, for few of the Mollusca or 
 Echinoderms range up into the Middle Chalk above. 
 
 In Ireland the Pecten asper sand is succeeded by yellowish 
 calcareous sandstones with nodules of chert, and varying 
 from five to thirty feet in thickness. These sandstones 
 are probably of the age of our Grey Chalk, the beds below 
 being the equivalent of our Chalk Marl (see ante, p. 173). 
 
 The Middle Chalk has at its base a hard nodular rock, 
 which passes up into firm rocky chalk that consists largely 
 of broken and triturated fragments of Inoceramus shells, 
 with many cells of Foraminifera. Higher up the chalk is 
 softer and whiter, and microscopical examination shows 
 that the shell-fragments become fewer, and the Foramini- 
 fera become less robust, having smaller and thinner shells ; 
 the mass of the rock consisting of a fine amorphous cal- 
 careous sediment. Toward the top of this division there 
 is something like a reverse change, the Foraminifera be- 
 coming more abundant, and at the same time rather more 
 robust. 1 
 
 This soft white chalk is evidently the deposit of a deep 
 sea at a considerable distance from land, but it contains 
 thin interstratified seams of marly shale, and it is impor- 
 tant to observe that the argillaceous element in these seams 
 increases northwards, till in Lincolnshire and Yorkshire 
 they are veritable clays, dark grey or black, and yet only a 
 few inches thick. Again, therefore, we seem to have evi- 
 dence of the occasional influx of currents from the north. 
 
 The Middle Chalk is surmounted throughout the greater 
 part of England by one or more beds of hard cream-coloured 
 limestone, which is known as the Chalk Rock, and has every 
 
 1 For these particulars I am indebted to my friend, W. Hill, F.G.S., 
 whose microscopical studies have greatly added to our knowledge of 
 the minute structure of the Chalk, and who has found that the successive 
 zones exhibit constant lithological differences. 
 
CHAP. X.] CRETACEOUS PERIOD. 177 
 
 appearance of having been formed in much shallower water. 
 Fossils are often abundant, G-asteropoda are not uncom- 
 mon, and include such genera as Turbo, Cerithium, Avellana, 
 Aporrhais, Natica, Crepidula, and Emarginula, the modern 
 representatives of which do not live in deep water, some 
 not ranging below 100 fathoms, and none lower than 150 
 fathoms. Moreover, some of the species are indistinguish- 
 able from those of the Chalk Marl nearly 400 feet below. 
 The rock also contains numerous grains of glauconite, and 
 includes layers of large green-coated nodules. 
 
 This sudden recurrence of peculiarities which charac- 
 terize the Chalk Marl and Totternhoe Stone, associated 
 with a fauna of similar character, compels us to conclude 
 that the sea had again become shallower by the rise of a par^ 
 of its floor ; there is, however, no sign of strong current- 
 action or of the' proximity of land. The compact rock and 
 its contents seem to have accumulated slowly in very quiet 
 water under conditions which permitted a large number of 
 marine animals to migrate eastwards, and repopulate the 
 bed of the sea. 
 
 This rock continues with little change as far westward 
 as the Chalk extends in England, but in Ireland there is 
 nothing which exactly corresponds to it, or to any part of 
 the Middle Chalk. Some of the fossils of this division 
 occur, however, in certain glauconitic sands and marls 
 which lie between the Cenomanien sandstones and base of 
 the Upper Chalk ; they vary from six to sixteen feet thick, 
 they contain large grains and occasionally pebbles of quartz, 
 and have evidently been formed in shallow water not far 
 from land. 
 
 The Scotch deposits are still more abnormal, for the beds 
 corresponding to the Irish Cenomanien are succeeded by 
 white sandstones from 30 to 100 feet thick, without fossils, 
 but including a seam of coal, and thus evidently formed in 
 close proximity to land. 
 
178 NEOZOIC TIME. [CHAP. X. 
 
 Above the Chalk rock of England there are a set of 
 rough nodular and shelly beds of a yellowish tint, in which 
 Echinoderms of the genus Micraster are extraordinarily 
 abundant, and these pass up into soft white chalk with 
 numerous layers of flints. Still higher is a considerable 
 thickness of chalk without flints, surmounted by other 
 beds in which they abound. The thickness of this Upper 
 Chalk increases from west to east, its total thickness near 
 Dorchester being estimated by Dr. Barrois at 500 feet, while 
 in the Isle of Wight it is about 700, and in Norfolk pro- 
 bably 900 feet ; even here, however, the actual summit is 
 not reached, the very highest or Maestricht chalk not 
 occurring in England. 
 
 t In Ireland the base of the Upper Chalk is a hard lime- 
 stone full of green grains and quartz pebbles, but holding 
 Echinoderms of Upper Chalk species. It appears, in fact, 
 to be the condensed equivalent of the two lowest zones of 
 the English Senonien, which are 250 feet thick in the south 
 of England, whereas the Irish bed is less than three feet. 
 Above there is hard white chalk which, however, is less 
 than 100 feet thick, though it must represent some 600 
 feet of the English Chalk. The same hard white limestone 
 is found at a few places on the west coast of Scotland, in 
 Mull and Argyleshire. 
 
 2. Geographical Restoration. 
 
 Lower Cretaceous Time. We have seen that at the close 
 of the Jurassic period the area of deposition was limited 
 to a region south of the latitude of Devizes and Chatham. 
 Everywhere to the north of this line there is a gap and un- 
 conformity between the Jurassic and Cretaceous rocks ; and 
 we may conclude that the greater part of the British area 
 was then in the condition of dry land. The areas occupied 
 by the Palaeozoic rocks formed hilly and mountainous 
 
CHAP. X.] CBETACEOFS PERIOD. 179 
 
 ground as they do now, and between these districts over 
 the Midland counties of England, and over the space now 
 occupied b j the Irish Sea, and thence by the North Channel 
 round the west of Scotland, spread a fertile lowland dis- 
 trict formed of the newly emerged Jurassic strata. 
 
 In the Wealden area an extensive series of freshwater 
 deposits was in process of formation, a series which is 
 generally spoken of as the delta of a great river, and is 
 usually compared with the deltas of rivers like the Nile 
 and Mississippi, which empty themselves into the sea. It 
 does not seem likely, however, that the area occupied by the 
 Wealden beds was the head of a marine gulf or bay, for it 
 is difficult to see in which direction it could have commu- 
 nicated with the open sea ; the absence of Neocomian de- 
 posits over Belgium and the north of France points to the 
 existence of land on the east, and there is no reason to sup- 
 pose that the Palaeozoic areas of Devon and Cornwall were 
 then separated from those of north-western France by 
 anything deeper than the valley of a river. Moreover, 
 the delta of a large river entering the sea is generally, if 
 not invariably, composed of alternating estuarine and 
 freshwater beds, whereas the Wealden series is entirely of 
 freshwater origin ; hence many have regarded the formation 
 as a purely lacustrine one. 
 
 Such a fluvio-lacustrine origin has especially been advo- 
 cated by Mr. C. J. A. Meyer, who remarks, 1 that although 
 there is considerable variation in the characters of the 
 Wealden deposits, "yet one might venture to say that 
 nine-tenths of the whole was quietly accumulated. The 
 fine-grained sandstones and quartzose grits of the lower 
 beds, the stiff red clays of the middle, and thinly foliated 
 ' marls with Cypris ' of the Upper Wealden might all be of 
 lacustrine origin, and yet include both tree stems and the 
 bones of reptiles. There is indeed in these again, as in 
 1 " Quart. Journ. Geol. Soc.," vol. xxviii., p. 247. 
 
180 NEOZOIC TIME. [CHAP. X. 
 
 some portions of the Purbeck series, a strong resemblance 
 to the Tertiary lacustrine beds of central France." 
 
 From the nature and fossil contents of the lower and 
 middle beds, he infers that the waters were at first shallow 
 and frequently disturbed by the currents of inflowing rivers ; 
 " the finely laminated strata of the Upper Wealden, on the 
 contrary, are such as belong to deeper waters, and rarely, if 
 ever, show traces of disturbance." These considerations 
 lead us to conclude that during the earlier part of the 
 Wealden epoch the country was still rising, and that the 
 Wealden rivers then attained their maximum velocity and 
 carrying power ; for a time perhaps the land was stationary, 
 but subsidence quickly ensued, diminishing the river- 
 action, increasing the area of the Wealden lake, and adding 
 depth to its central waters. 
 
 The history of the Purbeck- Wealden episode may there- 
 fore be summed up as follows : The Purbeck series was 
 formed during upheaval in lagoons that were gradually 
 cut off from the retreating sea ; the Lower Wealden beds 
 were formed in a freshwater lake on the site of the old 
 lagoons, and the level of its waters was maintained by the 
 influx of one or more powerful rivers ; the Upper Wealden 
 was formed during a subsidence which widened the area of 
 the lake, and eventually depressed it beneath the waters of 
 the returning sea. 
 
 The next point which calls for consideration is the 
 drainage system of the Wealden land, and whether it is 
 possible to ascertain the direction from which the principal 
 river or rivers ran into the lake. It must be remembered 
 that in passing from the Purbeck to the Wealden we find 
 evidence of rapidly increasing fluviatile action, as if some 
 large river had suddenly invaded the lake, or as if rivers 
 which had previously carried little but matter in solution 
 now became loaded with a quantity of detritus in suspen- 
 sion. Possibly both operations really took place. It has 
 
CHAP. X.] CRETACEOUS PERIOD. 181 
 
 been pointed out (p. 160) that in Purbeck times the valleys 
 of the English and Bristol Channels were in all probability 
 occupied by rivers of considerable size, but that on the first 
 emergence of the land the amount of mechanically-trans- 
 ported detritus which they carried seaward seems to have 
 been very small. Not only was the land at a comparatively 
 low elevation, for we must remember that during the 
 Jurassic period the height of the Welsh hills must have 
 been diminished by the accumulation of at least 2,000 feet 
 of strata round their flanks ; but it is also very likely that 
 small lakes existed in their upper reaches, which would in- 
 tercept and retain the detritus carried by the stream, just 
 as the mud of the Rhone is deposited in the Lake of G-eneva. 
 As, however, elevation proceeded and the land rose higher 
 above the sea, rainfall would be increased, erosion would 
 be accelerated, the load carried by the streams would be 
 larger, and the volume and velocity of the currents would 
 be greater, any lakes that existed would be rapidly filled up ; 
 under such conditions a large quantity of detritus would be 
 carried to the mouth of the rivers and poured into the Weal- 
 den basin. This will sufficiently account for the differences 
 observable in passing from the Purbeck to the Wealden 
 beds. 
 
 If, however, these western rivers were the only streams 
 that ran into the lake, we should expect the sandstones to 
 diminish eastward, but this is not the case, the Lower 
 Wealden of Sussex being more sandy than that of Dorset ; 
 and these Sussex sands must, I think, have been brought 
 by minor streams which drained the land on the north side 
 of the lake a supposition which finds confirmation in the 
 pebble bed of Lindfield (p. 165). It is also possible that a 
 stream may have entered the eastern end of the lake, for, as 
 we shall presently see, its outlet is not likely to have been 
 in that direction. 
 
 We must not forget the possibility of a great river 
 
182 NEOZOIC TIME. [CHA.P. X. 
 
 coming in from the north-west, as Dr. A. G-eikie briefly sug- 
 gests ; 1 that such a river must have traversed the north- 
 western plains on their upheaval from the Jurassic sea was 
 pointed out in the last chapter, and it was supposed that a 
 lake then existed on the site of the Irish Sea, and received 
 the detritus brought down by this stream. It was sug- 
 gested that it continued a south-easterly course over the 
 Jurassic clays, and discharged a large volume of water, but 
 a small amount of sediment, into the Purbeck gulf. In 
 Wealden time it may have carried a larger quantity of 
 sediment, though we can hardly attribute the sands of the 
 Lower Wealden to the influx of such a river, for after so 
 long a course over a low-lying clayey country its current 
 would not be likely to carry anything coarser than mud, 
 unless it was joined by powerful tributaries from Wales. 
 
 We may therefore conclude that the principal rivers 
 flowing into the Wealden lake came from the west and 
 north-west, draining the large tract of country which then 
 connected Brittany and Cornwall with Ireland. Other 
 streams of smaller volume, but carrying much detritus, 
 flowed in on the north and north-east. To the position of 
 the outlet we are guided chiefly by the disposition of the 
 overlying beds, and the tract over which they are most 
 deeply accumulated being on a line from the Isle of Wight 
 through the Paris basin, we may consequently assume that 
 the excurrent river ran from a south-eastern prolongation 
 of the lake, and, passing across France, fell into a gulf of 
 the Neocomian sea that stretched northward as far as 
 Vassy-sur-Marne. 
 
 Next let us endeavour to estimate the area over which 
 the Wealden deposits originally extended, which is of 
 course nearly the same thing as estimating the size of the 
 lake itself. We know that these strata extend from the 
 centre of Dorset to the Boulonnais, a distance of nearly 
 1 " Textbook of Geology," first edition, p. 817. 
 
CHAP. X.] CBETACEOUS PEBIOD. 183 
 
 200 miles. The rapid thinning out of the beds in Dorset 
 shows that they did not reach much farther due east, but 
 it is very likely that the lake was prolonged some distance 
 to the south-east along the axis of the Channel valley, and 
 there can be little doubt that its waters covered a large 
 part of the area which now lies between England and 
 France. It is not assuming much, therefore, if we sup- 
 pose that the Wealden beds spread as far south of our 
 present coast-line as they do to the north of that line. 
 Now from the coast of Dorset they are known to reach 
 inland for thirty miles, and in Hampshire a line joining the 
 Vale of Wardour with the North Downs is forty miles 
 north of the south coast of the Isle of Wight. If, then, we 
 assign the beds an original length of 200 miles and an 
 average breadth of seventy miles, we obtain an area of 
 14,000 square miles for their original superficial extent. 
 The area may have been somewhat larger, because we do 
 not yet know anything of their extreme southern or 
 northern limits, but, on the other hand, there is reason to 
 think that the eastern end of the lake was not so wide as 
 the western. See map, fig. 4. 
 
 The Wealden Beds have often been spoken of as if they 
 were one massive and continuous delta, and as if a calcula- 
 tion of the area over which they were spread out would 
 give us the superficial area of this delta a misconception 
 which has probably arisen from the idea that the beds 
 were formed in the estuary of a great river. If, however, 
 as is most probable, they were formed in a lake, it is 
 obvious that a massive formation might be accumulated 
 in the lake-basin while only small portions of that basin 
 were filled up by the deltas of the inflowing rivers, so as 
 to be raised above the level of the waters, and it is clear 
 that we can form no idea of the size of these deltas from a 
 calculation of the area of the lake-basin itself. Nay, 
 further, would not the size of these deltas be mainly 
 
CHAP. X.] CRETACEOUS PERIOD. 185 
 
 dependent on the movements of the land as influencing 
 rainfall, erosion, and transportation of material ? 
 
 From the considerations already stated, it is probable 
 that the actual deltas would attain their maximum develop- 
 ment in early Wealden times, while the land was rising or 
 stationary, and it is even possible that at one time a large 
 portion of the lacustrine area may have been silted up, and 
 the whole made very shallow ; but when the land began to 
 subside erosion and transportation would be checked, 
 though the volume of water filling the river-channels 
 might still . be large ; the level of the lake-waters would 
 probably rise, and the surface extent of the deltas would 
 be greatly reduced, if they were not submerged altogether. 
 Toward the close of the lake's existence this seems to have 
 been the case, the shaly clays of the Upper Wealden indi- 
 cating quiet deposition in the still waters of a lake that 
 was being gradually lowered toward the level of the sea. 
 
 As already stated, the deposition of the Wealden Beds 
 was contemporaneous with the formation of the marine 
 Neocomian strata of France and Germany. The Germanic 
 sea was extending itself eastward, and a gulf connected 
 with it lay over the east of Yorkshire and Lincolnshire. 
 At the same time the southern sea was gradually creeping 
 up the valley of the river which ran from the Wealden 
 lake, and the distance between the lake and the sea was 
 gradually lessened, till at length the last barrier was 
 broken through, and the Wealden lake became the Vectian 
 gulf or estuary. The change from the lacustrine shales of 
 the Wealden to the marine clay of the Lower Vectian is a 
 sudden one, and in this respect is like the change from the 
 Triassic marls to the Ehaetic beds ; but the actual condi- 
 tions of the two cases were very different, the area of the 
 Wealden lake was very much smaller, and its conversion 
 into a gulf was not accompanied by the tremendous cliinatal 
 change which took place in the earlier time, when the 
 
186 NEOZOIC TIME. [CHAP. X. 
 
 Triassic deserts were converted into fertile and forest-clad 
 districts. The land of Vectian time was doubtless similar 
 in climate and aspect to that of Wealden time, and the 
 plants and creatures which inhabited the country were the 
 direct descendants of those that lived in the Purbeck and 
 Wealden periods. 
 
 The geography of the British area had now become 
 similar to what it was at the close of the Portlandian epoch. 
 There were two gulfs, one on the south, in which the Ather- 
 field Clay and Walpen Sands were accumulated, and one to 
 the north-east, in which the middle part of the Speeton 
 Clay was contemporaneously deposited. For a certain time 
 after the first invasion of the Wealden lake the land seems 
 to have been nearly stationary, so that this basin was 
 gradually silted up, and shallow- water conditions prevailed 
 till further subsidence took place. Thus in Oxfordshire 
 and in Normandy (Pay du Bray), outside the limits of the 
 marine Lower Vectian Beds, we find freshwater deposits 
 similar to those of the Wealden, but probably of Vectian 
 age. 
 
 Marine erosion, however, was active, and, aided by further 
 subsidence, the sea spread farther and farther over the 
 ground which separated the two gulfs, till at length the 
 waves effected a junction across the lowest part of the 
 intervening isthmus and invaded the lacustrine area, which 
 seems at this time to have existed on the isthmus, and in 
 which the Shotover Sands were formed. The communica- 
 tion thus established became a narrow strait or channel, 
 through which a strong current ran from the northern to 
 the southern sea (see p. 169). This channel doubtless in- 
 creased in width, but there is no evidence that the sea had 
 encroached very far either on the eastern or western land 
 before the formation of the G-ault, which overlaps the Vec- 
 tian sands in both directions. Its western coast evidently 
 consisted of Upper Jurassic rocks, and it is probable that 
 
PLATE IX. GEOGRAPHY OF THE LATER PART OF THE VECTIAN EPOCH 
 (APTIEN STAGE). 
 
CHAP. X.] CRETACEOUS PEEIOD. 187 
 
 the actual shore did not lie very far beyond the present 
 limits of the Vectian sands, but ran in a N.N.E. direction 
 from near the position of Oxford through Northampton, 
 Eutland, and Lincoln. This phase of Cretaceous geography 
 is represented in Plate VIII. 
 
 Upper Cretaceous Time. We have now to chronicle 
 the phases of the great subsidence which commenced at 
 the epoch of the G-ault, and continued throughout the 
 remainder of the Cretaceous period, until a thickness of 
 some 1,300 feet of sediment had been accumulated over 
 the Lower G-reensand. The thickness of the Upper Cretaceous 
 sediments, however, as compared with those of the lower 
 division, is no criterion of the relative duration of the two 
 eras, for the coarser sediments of the earlier portion of the 
 period must have been deposited far more rapidly than the 
 fine materials of the later era. Some idea of the time 
 occupied in the formation of the Chalk may be gained if 
 we remember that the accumulation of the Atlantic ooze 
 the modern analogue of the Chalk is a process so slow, 
 that it is doubtful whether a foot's thickness of it is de- 
 posited in a century ; at this rate 1,000 feet of chalk would 
 require 100,000 years for its formation, and if we assume 
 that chalk was accumulated twice as rapidly as the Atlantic 
 ooze is supposed to be, the figures (50,000 years) still re- 
 present an enormous length of time. 
 
 Considering the depth of Gault clay which overlies the 
 eastern Palaeozoic area, and the manner in which the Gault 
 and Greensand overstep the members of the Jurassic system 
 westward, it is evident that the eastern part of the British 
 region subsided much more rapidly than the western, so 
 that the Jurassic strata were bent down, as it were, beneath 
 the advancing Cretaceous sediments. The waves of the 
 Cretaceous sea cut obliquely across the older strata, form- 
 ing a plane of marine denudation which was carried rapidly 
 westward, and had a gentle slope or inclination eastward. 
 
188 NEOZOIC TIME. [CHAP. X. 
 
 The first result of the great subsidence was the sub- 
 mergence of the promontory which existed on the site of 
 our eastern counties, and the outspread of the Gault muds 
 over the whole of south-eastern England ; at the same 
 time the western shore of the Cretaceous sea was carried 
 back to Devonshire, and doubtless also to the borders of 
 Wales, though subsequent detrition has destroyed all 
 evidence of the shore-line north of Devon. From the 
 present disposition of the Cretaceous strata, however, we 
 can hardly avoid the conclusion that the whole of central 
 England was once more converted into a sea-bottom, 
 on which sandy and glauconitic deposits were laid down, 
 just as such deposits are now formed along the bor- 
 ders of our great oceans at a certain depth and distance 
 from shore. Such deposits everywhere underlie the Chalk, 
 but we cannot regard them all as of the same absolute age, 
 because they were formed in a sea which was continually 
 spreading further and further to the west and the north, 
 so that the conditions which prevailed in England at the 
 epoch of the Gault and Upper G-reensand did not reach 
 Ireland till the time of the Lower Chalk, and no true 
 chalk was formed in that area till the time of our Upper 
 Chalk. 
 
 At the close of the English Greensand stage, when the 
 Warminster beds were being deposited, the whole of south- 
 eastern and central England was covered by a shallow 
 sea, nowhere apparently more than 100 or 150 fathoms 
 deep, and gradually shallowing westward. In the south- 
 west it stretched to the borders of Dartmoor, and it washed 
 the foot of the North Devon and Quantock Hills ; the 
 valley of the Bristol Channel was a deep inlet, and thence 
 the shore-line swept northward below the hills of Glamor- 
 gan, Monmouth, and Hereford. The height attained by 
 the Greensand in the Blackdown Hills is not more than 
 600 feet, and these are on the same line of longitude as the 
 
CHAP. X.] CRETACEOUS PERIOD. 189 
 
 eastern escarpment of the South Welsh coal-basin. It may 
 be that the south of England has been affected by subse- 
 quent subsidence to a greater extent than Wales, but the 
 difference can hardly be more than 300 feet, so that we 
 might guess the level to which Greensand formerly reached 
 in Monmouthshire to be about 900 feet. 
 
 But in speculating on the possible course of this coast- 
 line further north, and on the probable limits of the sea in 
 which the Upper Greensand was formed, we must remember 
 that the Lower Greensand or Vectian sea seems to have 
 extended much farther west in the south of England than 
 it did over the Midland counties (see p. 186), that its 
 shore-line had a general north-easterly direction, and that, 
 consequently, for a certain length of time, the shore of the 
 Upper Cretaceous sea would have a parallel direction. We 
 may assume that the recession of this coast-line proceeded 
 at nearly the same rate so long as it lay along the strike of 
 the Jurassic strata, but the superficial extent of these strata 
 being so much greater in the Midlands than in Dorset or 
 Somerset, it is probable that when the sea reached the 
 borders of Devon its shore between latitude 52 and 53 
 did not lie farther west than the line of the Warwick and 
 Leicester coalfields ; and again, when the south-western 
 shore was carried back to the Palaeozoic rocks, the waves 
 may still have been attacking the mass of Triassic marls 
 and sandstones which must then have enveloped the coal- 
 fields of Stafford and Shropshire. 
 
 These Triassic beds would form a tract of land uniting 
 the Longmynd district to the Carboniferous region of 
 Derbyshire, and constituting a barrier that would for some 
 time resist the advance of the Cretaceous sea. We have 
 some reason, therefore, for supposing that from the hills 
 of Monmouth the shore of the Upper Greensand sea 
 trended north-eastward to Derbyshire, and passed up the 
 eastern side of the Pennine range, without gaining access to 
 
190 NEOZOIC TIME. [CHAP. X. 
 
 the basin of the Irish Sea. If the prevalent current set 
 from the south-west, this curve of the shore would tend to 
 give it an easterly course, so that it may have passed sea- 
 ward and eastward from over the north of Warwick, which 
 will account for the great eastward extension of the G-ault, 
 and also for its absence north of latitude 52 50 7 . 
 
 The geography above suggested and represented in the 
 map, Plate IX., assumes that the Pennine hills were not 
 submerged, and, as this is an important point, we may 
 consider it a little more closely. We know that the relations 
 of the Jurassic and Cretaceous strata in the north-east of 
 England are similar to those of their south-western equi- 
 valents ; it is clear that the Upper Cretaceous sea, aided by 
 subsidence, marched across the Jurassic ground and formed 
 a plane of erosion that sloped gradually up to the Palaeozoic 
 hills. Now at Grarraby, which is nearly the most westerly 
 point of the Yorkshire Wolds, the Red Chalk, or horno- 
 taxial equivalent of the G-ault, rests directly on the Lias at 
 an elevation of about 600 feet ; a few miles further west 
 it must have lain on the Trias, and thence the sea-floor 
 probably passed with a gentle slope to the foot of the 
 Pennine hills. How far the Red Chalk extended in a 
 westerly direction we cannot say, but sooner or later it 
 probably passed into a more littoral deposit ; comparatively 
 deep water (100 to 150 fathoms) may, however, have 
 continued to within a short distance of the shore-line, and 
 the Pennine hills probably rose up from the sea with a 
 steep slope, as the Riviera does from the G-ulf of Grenoa. 
 Thus, if the base of the Chalk reached to what would now 
 be a level of 900 feet over the edge of the Trias sic boun- 
 dary, and we suppose the water there to have been 600 
 feet deep, it would not have overtopped the Pennine hills, 
 which even now rise in many places to heights of over 
 2,000 feet, and in the Cretaceous period the watershed 
 must have been much higher than it is now. Hence I do 
 
PLATE X. CRETACEOUS GEOGRAPHY (SHOWING THE PROBABLE COAST-UN E 
 DURING THE FORMATION OF THE UPPER GREENSAND). 
 
CHAP. X.] CRETACEOUS PEEIOD. 191 
 
 not think that this range was submerged till the time of 
 the Middle or Upper Chalk. 
 
 The remarkable change, however, which takes place in 
 the character of the Eed Chalk when followed along the 
 northern face of the Yorkshire Wolds, and its partially 
 argillaceous condition at Speeton (see p. 171), are facts 
 which suggest that currents carrying fine silt came from a 
 north-easterly direction, and that their influence was felt 
 as far south as the north-east of Yorkshire. This conside- 
 ration leads us to infer that continental land existed at 
 some distance north and north-east of the present outcrop 
 a land which doubtless included Scotland and Scandinavia, 
 and would effectually shut out the Arctic currents ; it is at 
 the same time quite possible that its highest mountains 
 were snow- clad, and they may even have nourished glaciers 
 which reached far down the valleys toward the shores of 
 the great European Ocean. 
 
 There would at length come a time when the barriers 
 which limited the Greensand sea were breached and over- 
 topped, when Wales was nearly isolated, and the hills of 
 Devon and Cornwall converted into islands ; the sea then 
 spread to the north-west, over the areas of the older 
 Mesozoic rocks, to the north of Ireland and the west coast 
 of Scotland. The facts observed in connection with the 
 Chloritic Marl and Cambridge Greensand seem to tally 
 with what we might expect to be the results of such a 
 change. The currents would be altered, and it is probable 
 that strong currents would set either toward or out of the 
 straits between Wales and Derbyshire, and to the scour of 
 such currents the evidences of erosion at this epoch may 
 be due. 
 
 It is very difficult to say how far west this subsidence 
 carried the Cretaceous sea, or to what extent Ireland and 
 the north of England were submerged during the formation 
 of the Lower and Middle Chalk in southern England ; for 
 
192 NEOZOIC TIME. [CHAP. X. 
 
 though a thickness of over 400 feet of chalk was accu- 
 mulated in the south and east of England during this 
 time, it is probable that these were the areas of greatest 
 depression, and that the western and northern portions of 
 the British region did not sink to the same vertical extent. 
 We cannot judge of the levels reached by the Cretaceous 
 sea from the present relative levels of the Cretaceous strata 
 in Antrim and Mull, because these areas have undergone 
 an extensive local depression in Tertiary times, after the 
 outpouring of the great lava-streams under which the 
 Mesozoic strata are buried. We may be sure that in Pre- 
 Tertiary times the relative level of these districts was many 
 hundred feet higher than that at which they now lie, while 
 the height attained by the base of the G-reensand in Morvern 
 (Argyleshire) shows that the Cretaceous sea must have 
 covered considerable areas in western Scotland, and makes 
 it probable that all the lowland district was submerged so 
 as to form a strait or channel between the Highlands and 
 the southern uplands. The latter, with the Cheviot Hills 
 and the higher parts of Cumberland, Westmoreland, and 
 Yorkshire, must have formed a group of islands ; and it is 
 not unlikely that Ireland presented a similar appearance, 
 glauconitic deposits like those of Antrim being deposited 
 in the comparatively shallow waters between the islands 
 of the Irish archipelago. On this point we shall never 
 obtain definite information, but the very existence of such 
 deposits in Ireland and of chalk over so large a part of 
 England, makes it certain that no large areas of land then 
 existed, that the Cretaceous sea became more and more 
 oceanic, and that the British region had never been so 
 deeply submerged since the commencement of Neozoic 
 time. 
 
 The subsidence had, however, by no means attained its 
 maximum extent, for at the epoch of the Chalk Rock the 
 downward movement seems to have been arrested ; and if 
 
CHAP. X.] CRETACEOUS PERIOD. 193 
 
 the inferences drawn from the facts previously recorded 
 (p. 177) are correct, there was actually an uplift raising 
 the sea-floor in England till the water above it was not 
 more than 100 or 150 fathoms deep. There is no clear 
 evidence of any such oscillation in the Irish succession, 
 but the white sandstones of Morvern (see p. 177) do lend 
 some support to the view that the formation of the Upper 
 Chalk was preceded by a movement of elevation, so that 
 beds of estuarine origin, with the remains of something 
 like a terrestrial surface, are here intercalated between 
 marine deposits. 
 
 The subsequent subsidence must have been more rapid 
 and still more extensive than that which had previously 
 taken place, but we still find deposition prevailing more 
 in the east than the west, and it was not until 250 feet 
 of chalk had been accumulated over the Chalk Rock in the 
 east of England that true chalk began to be formed in 
 Ireland, and even then it was deposited so slowly that only 
 90 feet seem to have been accumulated in the time that 
 600 or 700 feet were formed in England ; we may, there- 
 fore, conclude that the western region was never so deeply 
 submerged as the eastern. 
 
 During the formation of this chalk it would seem that 
 little of England or Wales could have remained above the 
 level of the sea, for we must remember that such chalk i& 
 a deep-sea deposit, and is not now formed in water of less- 
 than 400 or 500 fathoms. If we suppose that at the epoch 
 of the Chalk Marl central Wales was already so submerged 
 that the sea-level stood at the 1,000 feet contour, that 
 during the subsequent subsidence 500 feet of chalk were 
 deposited around it, and that the highest bed of this chalk 
 had 400 fathoms (2,400 feet) of water over it, it is clear 
 that all the present surface of Wales would be under 
 water ; and even if we allow for subsequent detrition by 
 supposing that from 800 to 1,000 feet of rock has been 
 
 o 
 
194 NEOZOIC TIME. [CHAP. X. 
 
 removed since the Cretaceous period, there is very little of 
 the territory which, with the addition of this thickness 
 (viz., 1,000 feet on the mountains), would overtop a line 
 drawn 3,900 feet above the present sea-level. From this 
 rough calculation, therefore, we may infer that if any land 
 rose above the waves of the Upper Chalk sea on the site of 
 modern Wales, it merely consisted of a small area overlying 
 the present Snowdonian range. 
 
 The islands of the Irish archipelago were reduced to 
 smaller and smaller dimensions, and it is probable that 
 chalk once covered the greater part of the country, but 
 whether the whole of it was ever submerged we have no 
 means of ascertaining ; and the same may be said of the 
 south of Scotland. With regard to the Highlands, from 
 the position of the Chalk in Morvern, and from the beds of 
 flints associated with the Tertiary lavas, we may infer that 
 it originally covered all the lower parts of Argyle and 
 Inverness. Flints abound, and fragments of chalk are 
 not uncommon in the Glacial deposits of the eastern coast, 
 proving that " the Chalk must once have been in place at 
 no great distance, if, indeed, it did not actually cover part 
 of Aberdeenshire and the neighbouring counties." ] We 
 shall not, therefore, be assuming more than the facts war- 
 rant if we conclude that the central Highlands formed an 
 island in the sea of the Upper Chalk. 
 
 How far this sea extended northward it is hard to 
 guess, but some speculations have been hazarded even on 
 this point. It is certain that the greater part of western 
 and southern Europe was covered by an ocean which 
 seems to have had a wide latitudinal extension, and may 
 have been continuous from the southern part of North 
 America, across the Atlantic, and through Europe into 
 Asia. If this was the general trend and extent of the 
 Cretaceous ocean, we may reasonably suppose the larger 
 1 A. Geikie, l: Scenery of Scotland," 1887, p. 125. 
 
CHAP. X.] CRETACEOUS PERIOD. 195 
 
 land areas of that period to have had a similar trend, at 
 any rate in the northern hemisphere, and to have spread 
 from east to west rather than from north to south like our 
 present continents. It is probable, therefore, as Professor 
 Prestwich suggested, 1 that a great northern continent 
 stretched across what is now the shallower part of the 
 North Atlantic Ocean, between Norway and Greenland, 
 forming a barrier which excluded the colder waters of the 
 Arctic seas, and allowed the Cretaceous ocean to have the 
 full benefit of the warmer currents from the south. 
 
 1 Pres. Address to the Geol. Soc., 1871 ; " Quart. Journ. Geol. Soc.," 
 vol. xxvii. p. Ixviii. 
 
CHAPTER XI. 
 
 HANTONIAN PERIOD. 
 
 HAYING- elsewhere stated my conviction that the 
 Lyellian divisions of Tertiary time cannot be re- 
 garded as systems or groups of equivalent geological value 
 to those which are recognized as divisions of Secondary 
 time, 1 1 need only here explain that no more than two such 
 Tertiary systems can be admitted ; for the first of them, in- 
 cluding the Eocene and Oligocene series, the name Han- 
 Ionian has been proposed, and for the second, which in- 
 cludes the Miocene, Pliocene, and Pleistocene series, the 
 name Icenian has been suggested. The same nomencla- 
 ture will be used in the present volume ; and it may be ob- 
 served that the importance of the break between the Oli- 
 gocene and the Miocene has recently been recognized by 
 M. de Lapparent. 2 
 
 The simplest division of the British Eocene series into 
 groups of fairly equivalent value is as follows 3 : 
 
 jy ( Hordwell Sands and Barton Clay. 
 
 \ Bracklesham and Bournemouth Beds. 
 j f j Lower Bagshot Sands and London Clay. 
 
 ( Reading Beds and Thanet Sands. 
 
 1 Geol. Mag.," 1885, p. 293, and " Historical Geology," 1886, p. 36. 
 
 2 "Manual of Geology," 1886, second edition, pp. 1120, 1164. 
 
 3 This chapter was written before Professor Prestwich read his paper 
 " On the Correlation of the Eocene Strata " (" Geol. Soc. Proc./' Dec. 
 21, 1887), in which he proposes the same division of the Eocene series. 
 
CHAP. XI.] HA.NTONIAN PERIOD. 197 
 
 The Oligocene series may also be simply divided into : 
 
 Uroer<! HempsteadB6ds ' 
 1 Bembridge Beds. 
 
 Lower Headon Beds. 
 
 The Hantonian strata of north-western Europe occur in 
 several broad basins or trough- shaped areas separated by 
 parallel anticlines or regions of elevation. The most 
 northern of these is that which we know as the " London 
 basin," but which is really only part of a large trough- 
 shaped area extending from Belgium across the North Sea, 
 and terminating in Wiltshire ; the second is known as the 
 Hampshire basin, and a third as the Paris basin. 
 
 A study of all these areas is necessary for a proper com- 
 prehension of the geographical changes which took place 
 during the period, and the stratigraphy of the Paris basin 
 is especially important from the fact of that area lying 
 nearer to the southern shore of the Hantonian sea. 
 
 1. Stratigraphical Evidence. 
 
 Eocene. The gap between the Chalk and the Tertiaries 
 is not bridged over by beds of passage in any part of 
 England, but in Belgium and Denmark there are deposits 
 which show that the Cretaceous period was brought to a 
 close by a general upheaval of western Europe a change 
 which led to the expulsion of the Cretaceous fauna from 
 the European area, and the introduction of a very different 
 shallow-water assemblage, which we call the Eocene fauna 
 because it contains the ancestors of our modern shallow- 
 water European species. 
 
 In England, therefore, there is a considerable break 
 between the Cretaceous and Hantonian systems, but tl.e 
 upheaval which caused this break seems to have been such 
 a gradual and uniform movement that it did not lead to 
 
198 NEOZOIC TIME. [CHAP. XI. 
 
 any widespread unconformity, producing rather what may 
 be called a physical and palseontological hiatus, which is 
 intensified by the contrast between the characters of the 
 Chalk and the London Tertiaries. There is, however, a 
 certain amount of unconformity, arising probably from 
 unequal uplift and erosion during the unrepresented time, 
 for, as Dr. Ch. Barrois has pointed out, 1 " the centre of the 
 Tertiary basin of London does not correspond with the 
 centre of the Cretaceous basin of London. Norfolk, the 
 deepest part of the Cretaceous sea, would still have been a 
 depressed region after the Cretaceous if an upheaval of 
 this area or a greater depression of the southern part of 
 the basin had not modified this state of things before the 
 deposition of the Thanet Beds." 
 
 A consideration of the variations in the thickness of the 
 Chalk, as proved by deep borings in the London basin, 
 shows that the Chalk is thinnest beneath or near London, 
 and that it thickens in every direction from that centre, as 
 if the original uplift had produced a low and broad dome 
 which had its centre on the Surrey side of the Thames, 
 and was quite independent of the subsequent upheaval 
 which produced the axis of the Weald. Thus the Chalk 
 is thinnest at Streatham (623 feet) ; beneath London, and 
 thence northward as far as Loughton, it varies between 645 
 and 656 feet ; further north it thickens to 680 at Cheshunt, 
 and north-eastward to over 700 feet at Wickham Bishop 
 and to 890 at Harwich ; from London eastward it thickens 
 to 682 at Chatham, and is over 734 at Chartham, near 
 Canterbury ; westward it is rather thicker at Richmond 
 (671 feet) than below London, and at Bushey, to the north- 
 west, it is about 700 feet. 2 South-west, at East Horsley, be- 
 tween Leatherhead and G-uildford, it is 817 feet, and on the 
 
 1 " Recherches sur le Terr. Cret. Sup.," 1876, p. 179. 
 
 2 This thickness is obtained by adding the difference between the 
 level of the ground at the well and the height of the Tertiary outcrop 
 
CHAP. XI.] HANTONIAN PERIOD. 199 
 
 south of the Weald, near Brighton, it is as much as 958 
 feet. 
 
 I agree with Dr. Barrois in thinking that the highest 
 zones of the Chalk do not exist beneath the London area, 
 but entirely differ from his view that their absence is due 
 to original non-deposition. I see no reason to doubt that 
 such an oceanic deposit as the uppermost Chalk extended 
 continuously from Kent to Norfolk, and that its present 
 absence near London is the result of pre-Tertiary erosion. 
 
 The lowest Eocene group, the Lower London Tertiaries, 
 as they are sometimes called, is a somewhat complex one. 
 The lowest member (Thanet Beds) is in East Kent about 
 80 feet thick, and consists chiefly of sandy marl or 
 clay passing up into grey sand, with layers of calcareous 
 sandstone ; westward these beds are replaced by sharp 
 grey or buff sand, which is 40 feet thick near Woolwich, 
 but thins westward through Surrey, and has not been 
 traced continuously further than Leatherhead. Beneath 
 the London Clay they extend as far as Chertsey, and thence 
 the boundary appears to run north-east along a line by 
 Hampstead, Enfield, Epping, and Braintree, to beyond 
 Sudbury. The Thanet Sands are therefore limited to the 
 eastern part of the London basin. 
 
 The next subdivision is known as the Woolwich and 
 Reading Beds, and is a very variable set of deposits, but 
 has a much wider extension, for it occurs throughout the 
 London and Hampshire basins, and seems to have been 
 continuous originally across the intervening chalk ridges of 
 Hampshire. These beds exhibit three distinct types or 
 facies, and the geographical position and extent of these 
 types is of course an important consideration. 
 
 1. The first and most widely distributed type is that of 
 the Reading Beds, which prevail throughout the central 
 
 to the thickness of chalk pierced by the boring. For this and other 
 information on these borings I am indebted to Mr. VVliitaker. 
 
200 NEOZOIC TIME. [CHAP. XI. 
 
 and western parts of the Hampshire basin, and through the 
 western and northern parts of the London basin. They 
 consist of clays and sands, which are generally bright- 
 coloured and sometimes contain marine fossils at the base, 
 but in the higher beds plant-remains are the only fossils ; 
 layers of pebbly sand, often compacted into conglomerate, 
 are of frequent occurrence, the pebbles being always of 
 flint. 
 
 2. The second type is that of the Woolwich Beds, which 
 consist of dull or dark-coloured sands and clays, con- 
 taining estuarine and freshwater fossils ; pebble beds of 
 variable thickness also occur in them. This type only 
 occurs over a certain area from Guildf ord in Surrey to 
 Milton in Kent, and again at Newhaven on the southern 
 side of the Wealden anticline ; but it would be rash to 
 assume that it originally extended completely across the 
 Wealden district. 
 
 3. The third type is purely marine, and consists of light 
 grey and greenish sands, with very few pebbles ; it is only 
 fossiliferous in East Kent, but probably passes westward 
 beneath the Woolwich type. 
 
 The first type can be traced into the second along the 
 southern edge of the London basin, and the change con- 
 sists chiefly in the thinning-out of the mottled plastic 
 clays, and the setting-in above them of a bluish-grey 
 laminated clay, which contains freshwater and estuarine 
 mollusca as well as plant remains. Mr. G-ardner has 
 pointed out that the floras of these two clays differ 
 that of the upper clay resembling the London Clay flora 
 more than that of the lower clays and in his opinion 
 the Reading Beds are a distinct group, older than the Wool- 
 wich Beds, and formed in an independent area of de- 
 position. Mr. Whitaker and Professor Prestwich, how- 
 ever, do not agree with this view, and believe the two 
 groups dove-tail into each other. 
 
CHAP. XI.] HANTONIAN PERIOD. 201 
 
 The pebble beds which form such a marked feature in 
 the district to the south-east of London lie principally 
 above the main mass of the Woolwich clays and sands. 
 Eastward they appear to pass into marine sands with a 
 pebbly base, and they have been described by Mr. Whitaker 
 under the name of the Oldhaven and Blackheath Beds. 
 He has also shown that during their formation erosion 
 took place on an extensive scale, and that these pebble 
 beds sometimes cut through the whole of the underlying 
 Woolwich Beds, so as to rest upon the Thanet Sands. 
 Moreover, it seems probable that they extended beyond the 
 limits of these sands to the southward, overlapping them 
 and resting directly on the Chalk, just as the Woolwich 
 Beds do to the westward. 1 
 
 The very existence of such accumulations of flint pebbles 
 to a thickness of 40 or 50 feet in some places would lead 
 us to infer that they have been derived directly from the 
 Chalk, and consequently that part of the Chalk area lying 
 to the south of the London basin was then exposed to 
 erosion. 
 
 The London Clay and the so-called Lower Bagshot Beds 
 may be considered together, for there is much reason to 
 think that they are parallel formations, and that the sands 
 replace the clays towards the west and south-west. The 
 London Clay is a marine deposit, formed during subsidence 
 in the deeper part of a shallow sea. Its basement bed is 
 always sandy and pebbly, but the mass of the overlying 
 deposit in the eastern districts is clay. It would appear, 
 however, that the lower and middle parts of this clay 
 were formed in deeper water than the upper, or Sheppey 
 Beds, which only yield fossils of terrestrial origin, trans- 
 ported by rivers, namely, the fruits, seeds, and leaves of 
 plants in great abundance, together with occasional bones 
 of snakes, birds, and other terrestrial animals. The Lower 
 
 1 See " Quart. Journ. Geol. Soc.," vol. xxii. p. 419. 
 
202 NEOZOIC TIME. [CHAP. XI. 
 
 Bagshot Beds are chiefly sands with intercalated layers of 
 clay. There is generally a complete passage by gradually 
 increasing sandiness, or by such alternations from one 
 formation to the other. In these beds plant remains are 
 the only fossils found. 
 
 The London Clay attains its greatest thickness (480 feet) 
 in Essex and Kent, where the Lower Bagshots are thin, 
 and it must have spread over a large area to the north as 
 well as to the south of its present limits, for a boring so 
 far north as Yarmouth passed through 310 feet of it; 
 originally, therefore, it must have covered the greater 
 part, if not the whole, of Norfolk, and doubtless extended 
 far beyond the present line of the chalk escarpment 
 in Suffolk, Herts, .Bucks, and Oxford. When traced 
 westward through the London basin the clay becomes 
 gradually thinner. Thus, in the Bagshot and Aldershot 
 country it is only about 330 feet thick, but the beds 
 grouped as Lower Bagshot are here from 120 to 150 feet 
 thick, so that the total still reaches 480 feet. Moreover, at 
 Kamsdell, near Basingstoke, there is a mass of brown clay 
 30 feet thick in what are called Lower Bagshot Beds, but 
 the only reason for not calling this London Clay is the 
 presence of sand below it. 
 
 When traced westward from the longitude of Eeading 
 and Basingstoke, the whole of the Lower Eocene under- 
 goes such a rapid change and thinning out that we seem to 
 be approaching a shore-line in that direction, and we cer- 
 tainly find the limit of the area in which the London Clay 
 was formed. 
 
 Writing on the " Western End of the London Basin " in 
 1862, l Mr. Whitaker showed that near Marlborough the 
 London Clay is reduced to a thickness of 15 feet, but is 
 covered by a certain thickness perhaps 40 or 50 feet of 
 " Lower Bagshot " Beds ; still further west the basement 
 1 "Quart. Journ. Geol. Soc.," vol. xviii. p. 259. 
 
.'! 
 
 PQ o 
 c ns 
 
 
 3 
 
 11 
 
 u 
 
 P 
 
 I-&- 
 
204 NEOZOIC TIME. [CHAP. XI. 
 
 bed only of the London Clay remains, and this is directly 
 covered by sands and pipeclays of the Bagshot type. The 
 only conclusion Mr. Whitaker draws from this is that the 
 London Clay has thinned out ; but it seems to me that the 
 persistence of the basement bed of the London Clay below 
 the Bagshot Beds means something more, and proves that 
 sands replace the brown clays in other words, that the 
 Lower Bagshot Beds belong to the London Clay group, and 
 not to that of the Bracklesham Beds. 
 
 Fig. 5, which is reproduced from Mr. Whitaker' s dia- 
 gram, shows the rapid thinning out of the London Clay 
 west of Reading, and the superposition of the " Lower 
 Bagshot " on the Beading Beds. As the latter are also 
 very thin here, he thinks that the Lower Bagshot Beds 
 eventually overlapped them to the westward, so as to rest 
 directly on the Chalk a conclusion which is confirmed by 
 the abundance of " greywethers " on the Chalk Downs in 
 that direction, and by the presence of large rounded flints 
 as well as small pebbles in the " basement bed," which is 
 common to the sands and the London Clay. 
 
 With regard to the southern extension of the London 
 Clay group, there is every reason to suppose that it spread 
 completely through Hampshire into the southern basin. 
 At Southampton and at Whitecliff Bay the London Clay is 
 just over 300 feet, and the " Lower Bagshot " is about 50 
 or 60 feet ; but at Alum Bay the former is only 200, and 
 the latter increases to 248. Noting this replacement, and 
 the fact that the plant remains of the Lower Bagshot Beds 
 are more nearly related to those of the London Clay than 
 to the flora of the overlying Bournemouth Beds, Mr. J. S. 
 Gardner suggested in 1882 that the Lower Bagshots 
 should be separated from the latter, and grouped with the 
 London Clay. 1 In Dorset the London Clay is very thin, 
 
 1 " Geol. Mag.," 1882, p. 470. Professor Prestwich has adopted a 
 similar line of argument in his recent communication to the Geological 
 
CHAP. XI.] HANTONIAN PEBIOD. 205 
 
 but beds of the Bagshot type are in great force at Stud- 
 land Bay and Corfe. 
 
 Layers of pipeclay containing plant remains are present 
 in the Lower Bagshot Beds, but are thicker in Dorset than 
 they are in the London basin. As such clays have generally 
 originated from the decomposition of granitic rocks, and 
 as such rocks occur to the westward, in Devon and Corn- 
 wall, we may take it as very probable that the materials 
 both of the clays and sands came from the south-west. 
 
 The geographical changes which seem to have taken 
 place during the Eocene period cannot be properly under- 
 stood without a study of the deposits in the Paris basin. 
 In this area the Lower Eocenes are but feebly developed. 
 The Sands of St. Omer and Douai, which correspond to our 
 Thanet Sands, do not extend into the Paris basin, and as 
 there is no equivalent of our London Clay, the whole series 
 is represented near Paris by beds which are similar to our 
 Woolwich and Eeading group. For the following details 
 of the succession at Yaugirard, I am indebted to Mr. J. S. 
 G-ardner : 
 
 Feet. 
 
 Base of Calcaire Grossier . . . . . 
 
 Lower f ~^ ue c ^ avs and san( l s > ^h lignite . . 20 
 
 Eocene. ) Mottled P lastic cla 7 . . 13 
 
 I White marl with freshwater fossils . .16 
 
 Calcaire pisolitique (Cretaceous) . . . .10 
 
 Here the lignitic group is directly succeeded by the 
 representative of the Bracklesham, but elsewhere there are 
 sands (Sables de Cuise) which contain marine fossils, and 
 are probably about the age of the Lower Bagshot Beds. 
 Moreover, an outlier of London Clay occurs at Dieppe, so 
 
 Society, and has proposed that the Lower Bagshot should henceforth be 
 called the Londou Sands, but it may be questioned whether it would 
 not be better to retain the name of Bagshot for the lower, and to change 
 the designation of the middle and upper beds. 
 
206 NEOZOIC TIME. [CHAP. XI. 
 
 that we may assume this clay extended across the Channel 
 and into northern France. 
 
 The Bracklesham and Bournemouth Beds form a well- 
 marked group, which is most fully developed in the Hamp- 
 shire basin. At Bracklesham in Sussex they are wholly 
 marine, consisting chiefly of clays and green glauconitic 
 sands, which yield a large rnolluscan fauna of a much 
 more tropical aspect than that of the London Clay. Num- 
 mulites appear for the first time, and are very abundant in 
 some of the beds, while Alveolina and other Foraminifera 
 enter largely into the composition of certain layers of cal- 
 careous sandstone. At Whitecliff Bay the lower part has 
 a more estuarine aspect, and at Alum Bay nearly the 
 whole is estuarine and lignitic. At Bournemouth the 
 greater part is fluviatile and freshwater, the lower beds 
 containing a large and varied assemblage of plant remains. 
 
 Still further east, in Devon, there is a tract of lacustrine 
 beds which appears to be of the same age (Bovey Beds). 
 
 This series is represented in the London basin by the 
 Middle and Upper Bagshot Beds, which both contain 
 marine fossils of the Bracklesham type, but are lithologi- 
 cally more like the upper part of the Bournemouth series. 
 They only occur over small areas, and their combined 
 thickness is seldom over 200 feet, which is small as com- 
 pared with that of the group in Hampshire, where the 
 total thickness is over 600 feet. 
 
 Moreover, it is clear that this northerly attenuation is 
 due to the vicinity of a shore-line. In the middle group the 
 fossils only occur at certain horizons, and at certain localities 
 they are by no means abundant or general ; the green earths 
 are not always glauconitic, the colouring matter being fre- 
 quently carbonaceous, and removable by combustion or 
 elutriation. 1 Freshwater diatoms have been recently found 
 
 1 Kev. A. Irving, " Geol. Mag.," 1883, p. 404, and " Quart. Journ. 
 Geol. Soc.," vol. xliii. p. 379. 
 
CHAP. XI.] HANTONIAN PERIOD. 207 
 
 by Mr. Irving both in the Lower and Middle Bagshots, 
 as well as ferruginous concretions that retain impressions 
 of vegetable structures, as in the case of bog-iron ores of 
 the present day. 1 Lastly, pebbles in thin layers, and in 
 the form of pebbly sands, are frequent throughout the 
 Bagshot series, but especially in the middle and in the 
 lower part of the upper group. 
 
 All these facts afford strong evidence that considerable 
 changes in the relative levels of land and sea were going 
 on in the London basin. Mr. Irving believes that the 
 Lower Bagshots thin out to the north and north-west, 
 allowing the middle group to rest on an eroded surface of 
 the London Clay. 2 
 
 In Hampshire the Bracklesham Beds are succeeded by 
 the Barton Clay, which is nearly 300 feet thick, and is 
 rich in marine fossils. The fauna, however, differs con- 
 siderably from that of the Bracklesham, and recalls that 
 of the London Clay, many of the species being closely 
 allied to those of the Lower Eocene, as if they had been 
 perpetuated in some neighbouring province, and their 
 slightly modified descendants had returned to the British 
 Sea as soon as conditions had again become favourable ; 
 this immigration of new species, taken together with the dis- 
 appearance of the larger and more tropical-looking members 
 of the Bracklesham fauna, is a certain indication of some 
 important physical or geographical change. 
 
 The succeeding Hordwell Sands seem to have been 
 formed in gradually shallowing water, for they contain a 
 mixture of marine and estuarine species at the top, and 
 
 1 " Quart. Journ. Geol. Soc.," vol. xliii. pp. 378, 381. 
 
 2 This opinion is now apparently shared by Professor Prestwich, 
 whose paper on the correlation of the Eocene strata was read as this 
 volume was passing through the press. He includes the Lower Bag- 
 shot Beds in the Lower Eocene, and remarks that this series both in 
 England and Belgium is separated from the overlying beds by a well- 
 marked line of erosion. (See " Proc. Geol. Soc.," Dec. 21, 1887.) 
 
208 NEOZOIC TIME. [CHAP. XI. 
 
 pass up into the brackish and freshwater beds of the 
 overlying Oligocene series. 
 
 Whether the Barton Beds ever reached northward into 
 the area of the London basin we cannot tell, because of 
 the uncertainty that hangs over the correlation of the 
 Bagshot Beds ; it seems probable, however, that the Barton 
 Clay was a formation of much more limited extent than 
 the London Clay. 
 
 In the Paris basin the Bracklesham Beds are represented 
 by the Calcaire G-rossier, a limestone group about 100 
 feet thick, and containing numerous fossils. At the base 
 there is a layer of pebbles overlain by glauconitic sands 
 and limestones, and these by shelly and foraminiferal 
 limestones, which must have formed in clear water at a 
 considerable distance from land. The thickness of the 
 group is only about 100 feet, but they evidently correspond 
 to the whole of the Bracklesham and Bournemouth Beds, 
 for such limestones would be accumulated much more 
 slowly than deposits near the mouth of a large river. The 
 Calcaire G-rossier is succeeded by sands and sandstones, 
 with marine fossils of Bartonian type. 
 
 The French series, therefore, differs from ours chiefly 
 in the absence of the two great clay formations, the London 
 and Barton Clays, which are such conspicuous members of 
 our series. The former is consequently much thinner 
 than ours, and all the beds, except the Calcaire Grossier, 
 would seem to have been formed near a shore-line. The 
 Calcaire Grossier stands out among these shallow-water 
 beds, and marks the occurrence of an extensive subsidence, 
 while its fauna proves that this subsidence opened the- 
 way for the immigration of a new and more tropical or 
 southern fauna. 
 
 The only other region it is necessary to notice is that of 
 northern Ireland and western Scotland, where a very 
 different set of rocks was being accumulated. These dis- 
 
CHAP. XI.] HANTONIAN PERIOD. 209 
 
 tricts were the scene of tremendous volcanic eruptions, at 
 first from lofty volcanic cones, and subsequently, in all 
 probability, from huge gaping fissures, which now appear 
 as lava-filled dykes. The lavas ejected from these sources 
 form extensive sheets, which are spread out one over the 
 other, till in some places they still form a pile over 3,000 
 feet in depth. 
 
 At certain localities, in Antrim and in Mull, fl uviatile 
 deposits are intercalated between some of these lava-flows, 
 and consist of gravels, sandstones, and carbonaceous shales ; 
 the shales containing leaves of plants which prove to be of 
 Lower Eocene age, according to Mr. J. S. Gardner. 1 The 
 gravels consist chiefly of rolled flints and fragments of lava, 
 with some pebbles of grey quartzite. In Mull the river- 
 bed containing these deposits can be traced for a distance 
 of nine miles, and the width of its valley seems to have 
 been between a mile and a mile and a half when it was 
 invaded and filled with the lava-flow which now covers it. 
 This stream seems to have come from the north-west, and 
 " a restoration of the contours about the river- gravels 
 shows high ground to the south and east, coinciding with 
 the boundaries of the traps, with the river channel roughly 
 following the present outcrop of the Palaeozoic rocks in 
 the Ross. A spur of gneiss from Benmore, represented 
 by the gneiss of Gribun, Erisgeir, and Inch Kenneth, 
 directed its course westward, and there is but slight trace 
 of it along the shore of Torosay." 2 
 
 Another buried valley lies below the Scuir of Eigg, the 
 dark pitchstone of the Scuir resting upon a thick bed of 
 gravel, which fills a hollow or trench excavated in the 
 underlying basalts, and amongst the gravel are frag- 
 ments and branches of coniferous trees. This interesting 
 relic of an Eocene river was first described by Dr. A. 
 
 1 " Quart. Journ. Geol. Soc.," vol. xliii. p. 270. 
 
 2 Gardner, loc. cit., p. 286. 
 
 P 
 
210 NEOZOIC TIME. [CHAP. XI. 
 
 Geikie, 1 and in his words, " the hollow in which the shingle 
 lies is evidently the channel of an ancient stream which had 
 eroded the older basalts. At the time when this stream 
 was flowing the island of Eigg must have been joined to 
 some higher land, probably to the west or north-west, for 
 the stream brought down with it blocks of hard Cambrian 
 sandstone a rock not found in Eigg, but abundant on the 
 opposite island of Rum." Dr. G-eikie has also shown that 
 the thickness of rock removed from some of the Highland 
 valleys since the volcanic eruptions has been more than 
 3,000 feet, and that the valley in which Loch Lomond is 
 situated could not then have existed. From this we may 
 judge how much the general surface of the country has 
 been lowered since Eocene times ; and the large quantity 
 of flints in the gravels proves that large tracts of the sur- 
 rounding country consisted of chalk. It is, in fact, probable 
 (as stated in the last chapter, p. 194) that at this time 
 the whole of the central Highland region was fringed with 
 a broad, undulating mantle of chalk, and that the valleys 
 which now trench the gneissic rocks of this region were first 
 marked out by the Eocene streams which coursed over the 
 surface of these chalk plains. 
 
 Oligocene. Deposits of this age occur only in one part 
 of England, namely, Hampshire and the Isle of Wight, and 
 only the central portion of this series now remains, so that 
 no discussion of comparative stratigraphy is required except 
 in connection with the French and Belgian series. The 
 English deposits were evidently formed in the delta of a 
 large river which drained a western continent, and they are 
 often called the Fluvio-marine series. 
 
 The Headon group is truly fluvio-marine, having at the 
 base freshwater clays and limestones, in the middle estua- 
 rine and marine beds, and at the top estuarine and fresh- 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxvii. p. 309, and " Scenery of 
 Scotland," second edition, p. 152. 
 
CHAP. XI.] HANTONIAN PEBIOD. 211 
 
 water beds. The total thickness at each end of the Isle of 
 Wight is nearly the same (180 feet), but the central marine 
 beds thicken eastward at the expense of the others, and 
 are about 100 feet thick in Whitecliff Bay. The marine 
 band is also largely developed, and still more fossiliferous, 
 near Brockenhurst in Hampshire, so that the deepest part 
 of the estuary seems to have lain to the north and east of 
 the Isle of Wight. 
 
 The succeeding Osborne and Bembridge Beds are a vari- 
 able series of freshwater deposits with one or more layers 
 of estuarine oyster-beds. The Lower Bembridge or Osborne 
 Beds appear to be of lacustrine origin ; at Headon Hill 
 they have at the base a limestone full of siliceous concre- 
 tions, and a similar limestone, associated with calcareous 
 sandstones and ragstones full of freshwater shells, occurs 
 at the eastern end of the island ; the upper beds are red, 
 blue, and green clays, with intercalations of yellow and 
 white sands in the eastern area. These beds were formerly 
 estimated at 60 to 80 feet thick, but have recently been 
 proved to be double that thickness. 
 
 The Bembridge Limestone is a remarkable horizon. At 
 the west end of the island it is a single band of tufa- 
 ceous and concretionary limestone about 15 feet thick, the 
 lower part of which contains freshwater shells, while in the 
 upper part land shells and eggs of the larger snails are 
 found. Toward the east it is split up into several layers 
 of compact creamy limestone, which contain a mixture of 
 land and freshwater shells, and at Whitecliff Bay it is 
 immediately overlain by a marl which is full of oyster- 
 shells. These facts indicate the existence of a large shallow 
 freshwater lake or " broad " on the borders of the estuary, 
 and the gradual deposition in this lake of so much cal- 
 careous matter that parts of it were completely dried up. 
 Moreover, the number of the large tropical land snails is so 
 great that, as Mr. Gardner observes, their presence in such 
 
212 NEOZOIC TIME. [CHAP. XI. 
 
 quantity necessarily implies that there was a large and 
 varied flora in the jungles surrounding the lacustrine area. 
 Eventually, however, a submergence took place which 
 brought in the brackish waters of the adjacent estuary and 
 converted the greater part of the area into an oyster-bed, 
 for in Whitecliff Bay such a bed overlies the limestone. 
 The higher Bembridge beds are marls containing Cyrence, 
 Melanice, and other shells which lived in fresh and brackish 
 water ; and these marls are thicker in the eastern part of 
 the island. 
 
 The base of the Hempstead group is taken at a band of 
 black carbonaceous clay, which contains freshwater fossils 
 and plant remains and seems' to be the relic of an actual 
 terrestrial surface. At Hempstead it is succeeded by about 
 140 feet of variously coloured clays and shales, with fresh- 
 water and estuarine fossils, passing up into green and 
 brown clays with some purely marine fossils. 
 
 Mr. Clement Reid has recently discovered that the 
 Hempstead Beds have a much wider extension in the cen- 
 tral and eastern parts of the island than was previously 
 supposed, and moreover that they are thicker to the east of 
 the Medina river than they are at Hempstead. Thus the 
 lower beds, which at Hempstead are only 140 feet thick, 
 are at Wooton 180, and include a group of soft sands 
 about 50 feet thick. 1 
 
 Passing over to France, a somewhat similar series is 
 found in the Paris basin. A lower group answering to our 
 Headon Beds commences with a freshwater limestone (Cal- 
 caire de St. Ouen), above which are marine sands and 
 marls succeeded by gypsum with freshwater marls. The 
 next group consists of greenish marls with marine fossils 
 succeeded by thick sands and sandstones (Gres de Fon- 
 tainebleau), and these correspond to our Bembridge and 
 Hempstead Beds. The highest member is a freshwater 
 1 " Geol. Mag.," 1887, p. 510. 
 
CHAP. XI.] HANTONIAN PERIOD. 213 
 
 limestone (Calcaire de la Beauce), which is believed to be 
 newer than our highest Hempstead clays ; it appears to be 
 of lacustrine origin, and it covers a large area between the 
 basins of the Seine and the Loire. The whole series 
 extends westward into Normandy, and it is interesting to 
 find an outlier of them in the Cotentin, due south of the 
 Isle of Wight ; the Oligocene beds are here only 36 feet 
 thick, but are believed by M. Dollfuss to include represen- 
 tatives of the whole Parisian series. 
 
 In Belgium there appears to be a break and unconfor- 
 mity between the Eocene and Oligocene series, and the 
 latter present quite a different facies from the contempo- 
 raneous sediments of the Anglo-Parisian basin. They are 
 divisible into two groups only the Tongrien and the 
 Eupelien. The lower is about 100 feet thick, consisting 
 chiefly of sands with marine fossils, but including some 
 fluviatile beds. The higher (Rupelien) group is said to 
 overlap the lower beds and to contain fossils derived from 
 their erosion ; it consists of marine sands and clays, the 
 highest of which (Argile de Boom) is nearly 200 feet thick 
 at Eupel and somewhat resembles the London Clay. 
 
 2. Geographical Restoration. 
 
 Eocene Time. The gradual upheaval of the British 
 area, which took place at the close of the Cretaceous epoch, 
 continued until the greater part of our islands were raised 
 above the level of the sea, and they once more became part 
 of a continent which stretched far westward and south- 
 ward of their present limits. In imagining the aspect of 
 this land we must remember that a large part of it was the 
 upraised bottom of the Cretaceous ocean, and though, 
 doubtless, portions of the Chalk were removed by erosion 
 during upheaval, especially those which bordered the rising 
 
214 NEOZOIC TIME. [CHAP. XI. 
 
 coast-lines of Wales and other hilly districts, yet we must 
 suppose that the great sheets of Chalk which occupied the 
 intervening tracts suffered but little, and formed broad 
 plains uniting Wales to the Pennine range and Ireland to 
 England and Scotland. 
 
 The materials of which the Eocene and Oligocene strata, 
 consist are such as are derivable from the Chalk and from 
 the granitic and Palaeozoic rocks of the western districts. 
 It would seem, indeed, that they were derived from these 
 sources only, for not a chip or pebble of any Jurassic rock 
 has been found in them ; and there is therefore every 
 reason to suppose that the Jurassic, and probably the 
 Lower Cretaceous strata also, were deeply buried through- 
 out the duration of the Hantonian period. 
 
 As regards the general elevation of the country above 
 the sea at this epoch, if we bear in mind that the deepest 
 part of the Cretaceous sea lay over eastern England, and 
 the probability that Ireland was never so deeply sub- 
 merged as England, we may conclude that the elevation 
 which raised the eastern part of England into land must 
 have carried Ireland and West Scotland to a much higher 
 level above the sea than that at which they now stand. It 
 is quite possible that there was a difference of 500 fathoms 
 in the depth of the Cretaceous sea along the eastern and 
 western parallels of the British area, and if the subsequent 
 upheaval was approximately uniform, the upper surface of 
 the Irish Chalk would on these assumptions have been 
 raised to a level of 3,000 feet above the sea when the 
 Chalk of eastern England was raised to the sea-leveL 
 Moreover, it is a remarkable fact that our islands are 
 shown by the Admiralty charts to stand upon a submarine 
 plateau, the border of which runs outside the coasts of 
 France, Ireland, and the Hebrides; on this plateau the 
 soundings are everywhere under 100 fathoms (600 feet), 
 but from its surface the sea-bottom slopes steeply down 
 
CHAP. XI.] HANTONIAN PERIOD. 215 
 
 to depths of 1,300 and 1,500 fathoms (9,000 feet), as if its 
 edge had for a long time formed the coast-line of western 
 Europe. 
 
 Whether the west-European plateau was first upraised 
 in Eocene or in Trias sic time must remain doubtful, but 
 it is highly probable that the coast-line of the Eocene 
 land lay along the slope of this plateau, and that the 
 land then stood at a much higher relative level than it 
 does now; that is to say, the horizon of the Eocene 
 Atlantic cut the Eocene land at a level which is now 
 at least six hundred, and possibly several thousand feet 
 below the present sea-level. This high relative level 
 seems to have been maintained throughout the whole 
 period, and it is possible that the western and north- 
 western districts hardly participated in the oscillatory 
 movements which took place in the eastern areas of sedi- 
 mentation, but, being continuously exposed to detrition, 
 underwent more or less continuous elevation throughout 
 the whole period. There is no doubt that these districts 
 were at this time subjected to an immense amount of 
 erosion and detrition, and though denudation can hardly 
 be the primary cause of elevation, it is certainly calcu- 
 lated to accelerate it by removing material and thus 
 diminishing the weight to be lifted. Such a connection 
 between denudation and elevation has been pointed out 
 by several writers, notably Dr. Ch. Eicketts 1 and Capt. 
 C. E. Dutton. 2 
 
 The similarity between the Lower Eocene floras of Ire- 
 land, Scotland, Iceland, and Greenland is so great, and 
 the climate which they indicate is so temperate, as to 
 make it highly probable that these four countries formed 
 at this time a continuous tract of land. There is still a 
 submarine ridge connecting Scotland and Greenland over 
 
 1 " Geol. Mag.," 1883, p. 10. 
 
 2 " Nature/' 1879, vol. xix. p. 251. 
 
216 NEOZOIC TIME. [CHAP. XI. 
 
 which the soundings are seldom more than 500 fathoms, 
 and are more often between 300 and 400 ; this, then, may 
 indicate the site of the connecting land which existed 
 throughout Eocene, Oligocene, and Miocene times. To 
 effect such a union now would require an elevation of 
 about 3,000 feet, and it seems reasonable therefore to re- 
 gard this as a rough measure of the difference in altitude 
 between the base-levels of modern and Eocene Scotland. 
 If to this we add the present heights of Scottish moun- 
 tains, and allow 1,000 feet as the amount by which they 
 have been lowered since the commencement of Tertiary 
 time, we have a total of over 8,000 feet for the height of 
 many of these mountains in the Eocene period. 
 
 Volcanic activity is so often an accompaniment of eleva- 
 tion that we are not surprised to find that it was rife 
 throughout the whole of this region, and that great out- 
 pourings of basaltic lava occurred not only in Ireland and 
 Scotland, but in the Faroe Islands on the line of connec- 
 tion above-mentioned, as well as in Iceland and Green- 
 land. The denuded stumps of some of the great volcanoes 
 which existed at this time are found in Skye, Mull, Bum, 
 St. Kilda, and Ardnamurchan. The volcanoes of Skye 
 and Mull appear to have been on a grander scale than 
 the modern volcanoes of Italy ; Professor Judd estimates 
 that the base of the Mull volcano must have been at least 
 forty miles in circumference, and as Etna, from a base of 
 only thirty miles in circumference, rises to a height of 
 10,900 feet above the sea, he argues that if there was a 
 similar relation between the base and the altitude of the 
 Eocene volcano, the latter must have had an elevation of 
 at least 14,500 feet. Checking this by another calculation, 
 founded on the inclination of the lava-beds, he finds that 
 it could not have been less than 10,000 feet high. 
 
 The existence of valleys, watercourses, and river-beds 
 among these Eocene lavas proves the country to have been 
 
CHAP. XI.] HANTONIA.N PERIOD. 217 
 
 watered by a copious rainfall ; the contents of the gravel 
 beds prove that rapid erosion was in progress ; while the 
 plant remains show that the lower slopes of the volcanoes 
 and of the surrounding land were clothed with an abun- 
 dant vegetation. We must, therefore, picture a country in 
 which all the terrestrial agents of change were in full 
 activity, a country where fire and water frequently con- 
 tended for the mastery, where wide districts were from 
 time to time devastated by burning streams of lava, but 
 were soon restored to fertility by cooling showers and by 
 the irrigation of a thousand streams that sprang from 
 the slopes of cloud-capped mountains. 
 
 Coming now to the area within which sedimentation 
 was taking place, it is evident from a comparison of the 
 English and Belgian strata that Belgium came within the 
 influence of the Eocene sea before England did, and that 
 a depressive movement allowed the sea to advance westward 
 and to occupy portions of Kent, Surrey, Essex, and Suffolk, 
 at the time of the Thanet Sands. The area which these 
 sands seem originally to have covered is indicated in 
 Plate XI. by the finer blue lines, and this tract appears to 
 have been part of a large bay which extended from the 
 northern sea into the Anglo-French land region. 
 
 From the nature of the beds in East Kent the abun- 
 dance of glauconite grains, the admixture of calcareous 
 matter, and the presence of such shells as Pholadomya 
 we may infer that the sea was moderately deep in that 
 district; while the replacement of these beds by sharp 
 quartzitic sands to the westward proves the water to have 
 become shallower in that direction. From the purely 
 marine character of the beds we may conclude that the 
 sediment was carried by marine currents circulating round 
 the bay in the same manner as such currents now circu- 
 late in the North Sea. From the absence of pebble beds 
 we are justified in supposing the shores to have been low, 
 
218 NEOZOIC TIME. [CHAP. XI. 
 
 and it is more likely that they were bordered by sand 
 dunes than by chalk cliffs. 
 
 Passing now to the Reading Beds, we find evidence in 
 their wider extension of a further and more general sub- 
 sidence, which carried the sea over the whole of the London 
 basin, and southward over Hampshire into the southern 
 basin. In the shallow gulf thus formed were deposited the 
 marine basal beds of the Beading group, in which large 
 oysters are the most abundant shell, but there is no 
 evidence that these beds ever extended over the area of 
 the Weald, and very good reason to think that they did 
 not. 
 
 That the rise of the Wealden dome began in early 
 Eocene times is by no means a new idea. It was suggested 
 as long ago as 1852, by Professor Prestwich, in his paper 
 on the Thanet Sands, 1 though some of the data from 
 which he inferred its existence would not now be accepted ; 
 in 1866 Mr. Whitaker 2 remarked upon the southerly over- 
 lap of the Woolwich and Blackheath Beds, and at a later 
 date 3 we find him inferring from this " that the planing 
 down of the chalk which once spread over the Wealden 
 area began in Lower Eocene times, and that the pebble 
 beds of Bromley, Blackheath, &c., are one of the direct re- 
 sults of that denudation." 
 
 The very limitation of the Thanet Sands to the northern 
 side of the Wealden area seems to indicate the existence 
 of land, or at any rate of a large shoal, over that area 
 during their formation, and it is not at all improbable 
 that the depression of the Anglo-Belgian basin was con- 
 temporaneous with an uplift of the region which is now 
 the axis of the Weald and Artois. If this were so, and if 
 the force of the uplift was concentrated more especially on 
 
 1 " Quart. Journ. Geol. Soc.," vol. viii. p. 256. 
 
 2 Ibid., vol. xxii. p. 420. 
 
 3 " Mem. Geol. Survey," 1872, vol. iv. p. 241. 
 
CHAP. XI.] HANTONIAN PEEIOD. 219 
 
 the Wealden area, producing the first outline of the oval 
 or boat- shaped periclinal of this area, it is easy to under- 
 stand the relations of the several members of the Lower 
 London Tertiaries ; at first the shores would be low and 
 cliff-less, but the general submergence at the time of the 
 Woolwich and Eeading Beds would convert the Wealden 
 dome into an island, and the erosion of the waves along its 
 margin would lead to the development of cliffs, at the foot 
 of which shingle beaches would naturally be formed. 
 
 In this conclusion, and except as to the precise epoch 
 when the pebbles were first quarried from the chalk, I am, 
 indeed, only following Professor Prestwich's original view, 
 which is expressed as follows : l " From the foregoing con- 
 siderations it is probable that there was some extent of 
 dry land, possibly an island, somewhere intermediate 
 between a line drawn, on the north, from Farnham toward 
 Canterbury, and on the south from Winchester to New- 
 haven, and extending eastward into the north of France ; 
 and that the long- continued wear on its coast accumulated 
 on its shores extensive banks of pebbles, whilst the finer 
 sediment produced at the same time, in conjunction with 
 the debris brought down by operation of streams, formed 
 at a distance from the land the strata of this oldest Eocene 
 epoch." 
 
 Let us next consider the evidence of the plastic clays of 
 the Reading group, and the physical conditions which 
 their characters appear to indicate. It is the general 
 opinion that they are of freshwater origin. Their asso- 
 ciation with plant beds, and their actual intercalation be- 
 tween freshwater deposits near Paris, are strong pieces of 
 evidence in favour of this view ; but if they are fresh- 
 water beds, it is difficult to see how they can have been 
 
 1 " Quart. Journ. Geol. Soc.," vol. viii. p. 259. He then thought the 
 pebble beds were formed during the deposition of the Thanet Sands, 
 and were afterwards redistributed. 
 
220 NEOZOIC TIME. [CHAP. XI. 
 
 formed in anything but a large lake or series of lakes. 
 No one, perhaps, has studied them more carefully than 
 Professor Prestwich, and in 1854 he referred their forma- 
 tion to river-action on a large scale, and looked to the 
 granitic districts of the south-west for the supply of the 
 argillaceous material. 1 Mr. Gardner also speaks of them 
 as fluviatile ; but considering the area over which they are 
 known to extend in unbroken continuity, they can hardly 
 be called fluviatile deposits in the ordinary sense of the 
 term. That the lakes were shallow and prolonged into 
 extensive arms and inlets is very probable, and they were 
 doubtless fed by streams which had little velocity, but 
 meandered quietly over the plains of chalk that surrounded 
 the lacustrine areas, so that parts of the water-covered tract 
 might be regarded as expansions of the river valleys, and 
 in that sense fluviatile. 
 
 If this is a correct idea of the conditions under which 
 the Reading Beds and Plastic Clays were formed, it is 
 clear that some barrier must have been raised which pre- 
 vented the access of the sea that had at first occupied a 
 portion of the lacustrine area, for there cannot have been 
 much difference of level between the marine and the lacus- 
 trine waters. It is not difficult, however, to understand 
 the construction of such a barrier if the existence of land 
 over the Wealden area is granted, for this would itself 
 form a portion of the barrier, and the erosion of its shores 
 would afford a supply of flint pebbles and sand which the 
 set of the currents might carry northward and pile up in 
 the form of shingle banks and sand dunes across the 
 shallow waters of the London area. Seabord lakes and 
 alluvial levels, shut in and protected from the inroads of 
 the sea by such banks, are of common occurrence ; and it 
 is a curious coincidence that pebble beds should exist at 
 various horizons in the Woolwich and Reading Beds, and 
 1 " Quart, Journ. Geol. Soc.," vol. x. p. 136. 
 
CHAP. XI.] HANTONIAN PERIOD. 221 
 
 should be thickest across the middle part of the London 
 basin. The Hertfordshire conglomerate or pudding-stone 
 is a relic of one of these beds ; another is to be seen at 
 Lewisham, and the Blackheath Beds form an enormous 
 mass of shingle at a higher horizon. 
 
 If these pebbles had been brought by a large river from 
 the west or south-west, we should expect to find them 
 thickening in those directions ; but such is not the case, 
 they actually thin out westward as well as eastward, and 
 appear to be local deposits confined to the northern side of 
 the Wealden anticline. Mr. Whitaker has remarked that 
 the pebbles in the Blackheath Beds are always well worn 
 and rounded, and he infers that they were not formed as a 
 beach against a shore-line, for in such beaches there are 
 generally a certain number of subangular pebbles, but he 
 thinks they have been carried out some distance from the 
 actual shore, and only brought to rest after a long exposal 
 to the wearing action of waves and currents. This is 
 exactly what would happen under the geographical con- 
 ditions I have supposed. It is, however, quite possible 
 that many of the pebbles were rounded in the channels of 
 small rivers draining the Chalk island of the Weald 
 before they were brought down to the shores of that 
 island. 
 
 The freshwater beds of the Woolwich group, again, were 
 clearly formed in the estuaries and deltas of small rivers, 
 and there is no reason whatever for supposing that these 
 rivers came from the west, but much reason to think that 
 they drained a tract of land over the Wealden area. 1 They 
 only occur over a limited space on the northern and 
 southern sides of this area, and they are just such deposits 
 as might be formed in lagoons and in the estuaries of 
 rivers which drained into a land-locked bay. Moreover, 
 Professor Prestwich states that the prevailing dip of the 
 1 See Prestwich, " Quart. Journ. Geol. Soc.," vol. x. p. 135. 
 
222 NEOZOIC TIME. [CHAP. XI. 
 
 layers of false stratification in the Kentish and Surrey 
 beds is northward, or from the direction of the presumed 
 island, at angles varying from 10 to 35 degrees. 
 
 Throughout the time of their accumulation, and of the 
 overlying Oldhaven Beds, there is little evidence of any 
 general subsidence ; the probability is that the land was 
 practically stationary, but that the coast-lines were being 
 constantly altered by the action of tides, currents, and 
 winds, just as the eastern and southern shores of England 
 have been altered within historic times by the same 
 agencies, one tract of coast being worn away and cut back, 
 while at other localities the materials so obtained were piled 
 across the mouths of rivers and in front of low-lying shores. 
 
 This stationary period was succeeded by one of decided 
 and continuous subsidence, and the basement bed of the 
 London Clay represents the final distribution of the sand 
 dunes and shingle banks beneath the waters of the ad- 
 vancing sea, these barriers being destroyed, and the whole 
 lacustrine area behind them being at once covered by the 
 sea of the London Clay. 
 
 This submergence in all probability carried the Wealden 
 island far below the sea-level, for there seems no good 
 reason to doubt that the London Clay extended across the 
 whole of south-eastern England, and over the north- 
 western part of France, at least as far as the latitude of 
 Dieppe. 1 How far westward the coast-line was carried at 
 
 1 The sands on the North Downs, supposed by Mr. A. Irving to be 
 Upper Bagshot, are probably post-Eocene. How far the Ypresien 
 clay of Belgium reached southwards is uncertain. Professor Gosselet 
 indeed thinks it did not pass into France, and in his map (" Esquisse 
 Geol. du Nord de la France," PI. XII. A), shows a broad tract of land 
 extending from the Boulonnais to the Ardennes at this epoch ; but in 
 this, as in other cases, his restoration seems to have been constructed on 
 the assumption that the present boundaries of the beds are nearly coin- 
 cident with their original limits, very insufficient allowance being made 
 for subsequent denudation. 
 
PLATE XI. GEOGRAPHY OF THE LOWER EOCENE PERIOD. 
 
 The closer lines represent the sea of the Thanet Beds, and the wider lines that of the 
 London Clay. 
 
CHAF. XI.] HANTONIAN PERIOD. 223 
 
 this time is a very difficult point to determine. We know, 
 however, that in Wiltshire the London Clay thins out and 
 is replaced by sands (see Tig. 5), so that probably the sea 
 did not extend very far west of Marlborough, perhaps no 
 farther than the present position of the Chalk escarpment ; 
 thence it must have trended south-west to the western 
 border of Dorset, and north-east outside the present limits 
 of the Chalk, to the western border of Norfolk. The great 
 plain of the Fenland was then, of course, covered by a 
 continuous sheet of chalk, and there is no reason to sup- 
 pose that the Eocene strata overlapped this either west- 
 ward or northward. The probable limits of the sea at this 
 time are indicated on Plate XI. 
 
 The London Clay is a purely marine deposit, and does 
 not exhibit any traces of fluviatile action till we reach its 
 highest beds, but the material of which it consists is 
 usually supposed to have been brought down by some 
 large river. Sir Charles Lyell thought that this river 
 might have drained a continent that lay to the west or 
 south-west of Britain, and Mr. J. S. Gardner l has accepted 
 this view, though he does not urge any positive evidence in 
 support of it. The London Clay does not assume a more 
 estuarine facies either to the west or the south-west, but 
 seems merely to thin out and to be partially replaced by 
 sands. When we remember, indeed, that the locality 
 which has yielded the most distinct evidence of fluviatile 
 action lies to the east of London, there seems to be rather 
 a greater probability that the river which carried the fruits 
 to Sheppey came from an eastern quarter and drained 
 some portion of the European continent. 
 
 Here, however, we must ask whether the phenomena of 
 
 the London Clay really require the agency of a single large 
 
 river, and whether they cannot be equally well accounted 
 
 for on the supposition that several, if not many, rivers 
 
 1 " Proc. Geol. Assoc.," vol. ri. p. 92. 
 
224 NEOZOIC TIME. [CHAP. XI. 
 
 emptied themselves into the sea and contributed to its 
 formation. Is not the London Clay just such a lenticular 
 mass of mud as would be formed in the central and deeper 
 part of a rather shallow sea, into which many rivers poured 
 their load of sediment? Mr. Gr. F. Harris, who has studied 
 the Belgian strata, informs me that there is no evidence of 
 fluviatile deposits on a large scale in Belgium, or of the 
 influx of any large river from the east, but that the Belgian 
 geologists attribute the fluviatile and estuarine portions of 
 their Lower Eocene deposits to the influence of small 
 streams from the eastward. In the same way the river 
 by whose current the Sheppey fruits were carried may 
 have come from the land which lay over France to the 
 south, 1 but there is no reason to suppose that its volume 
 was greater than that of the Thames. We must remember 
 also that these Sheppey clays may be contemporaneous 
 rather with the Lower Bagshot Beds than with the London 
 Clay of the west. They may have been formed at a time 
 when much of the shallow sea-bed had again been con- 
 verted into a region of lakes, lagoons, and estuaries, partly 
 by the process of silting up, and partly perhaps by an 
 actual uplift of the northern part of the English area of 
 sedimentation. 
 
 It is certain that great geographical changes took place 
 during the formation of the Lower and Middle Bagshot 
 Beds, but until the stratigraphy of this part of the Eocene 
 series is more completely worked out, it would be rash to 
 speak at all confidently with regard to the results of 
 these changes. There is, however, much reason to believe 
 that the tract which had hitherto been the principal 
 area of deposition was raised, and that large parts of it 
 became dry land, while the Paris basin was correspond- 
 ingly depressed, and the Hampshire basin became an 
 
 1 This was Professor Prestwich's view in 1854 (see " Quart. Jouriu 
 Geol. Soc.," vol. x. p. 448), where he gives very good reasons for it. 
 
CHAP. XI.] HANTONIAN PERIOD. 225 
 
 estuary into which rivers from the west emptied them- 
 selves. 1 
 
 In the first pla.ee, the Lower and Middle Bagshots of the 
 London basin are certainly not the deposits of an open sea. 
 All who have recently studied these beds agree in regard- 
 ing the Lower Bagshot Beds as of freshwater origin and 
 either fluviatile or lacustrine deposits, and Mr. Irving 
 considers the middle group to be lagoon deposits in the 
 close neighbourhood of land, the waters of which were 
 kept in a partially saline condition by occasional intrusions 
 of the sea, and by percolation through fringing shingle 
 banks. 3 It is clear there was land to the north and 
 west of this area and open water to the south, but it is 
 probable that the ridge of the Wealden anticline was again 
 above the sea-level and contributed a share of the flint 
 pebbles that occur in the Middle and Upper Bagshot Beds. 
 
 Secondly, there are clear proofs in the strata of the 
 Hampshire basin that this area was a gulf which received 
 the waters and the sediment of one or more rivers ; rivers 
 which had doubtless contributed their quota of sediment 
 to the London Clay.- The changes of level which closed 
 the episode of this clay formation converted the head of 
 the southern gulf into a broad alluvial plain through which 
 the rivers slowly made their way to the sea and probably 
 opened out at intervals into lagoon or lake-like expansions. 
 Thus Mr. G-ardner is of opinion that the most western beds 
 of Corfe, Studland, and Alum Bay were accumulated in a 
 wide valley or shallow lake, and he remarks that "the 
 complexity of the stratification suggests that two rivers 
 united in this valley, and shows plainly that the waters 
 must, in any case, have been rapid at times, and subject to 
 periodical fluctuations of volume." He infers also, " from 
 the absence of lignites in some parts of the series, that 
 
 1 Gardner, " Proc. Geol. Assoc.," vol. vi. p. 95. 
 
 2 " Quart. Journ. Geol. Soc.," vol. xliii. p. 389. 
 
226 NEOZOIC TIME. [CHAP. XI. 
 
 there were, in the upper parts of the river, lakes such as 
 those of Bovey Tracey, which intercepted drifting timber ; 
 its abundance in other beds marking the time when these 
 had been filled in." After the completion of the geo- 
 graphical changes which took place during the formation 
 of the Lower Bagshot Beds, it is evident that the whole 
 area underwent a gradual subsidence which allowed the 
 sea to regain a part of its lost domain. To quote again from 
 Mr. Gardner : " In the Bournemouth Beds we have deposits 
 of the same river, but in a more open and level valley, and in 
 closer proximity to the sea. In all the lower or freshwater 
 series we have no sign of the presence of sea water, and 
 when we do find it in the higher beds to the east, it is not 
 that the river deposits encroached there on the sea, but 
 that the land gradually sank, and allowed the sea to cover 
 them." 
 
 " It is of great interest to trace through these beds the 
 change from a comparatively upland flora to a valley, and 
 then to a swamp flora ; to follow out the lowering of the 
 land until it became sea ; to trace the sea, first trickling in, 
 as it were, and forming lagoons, then overwhelming the 
 mud deposits formed by these lagoons, with shingle and 
 sand ; to realize, in fact, the actual shore-line, now marked 
 by river deposits, full of plant remains on one side, and a 
 sea fauna with sharks' teeth on the other. 
 
 " The series of marine beds from Bournemouth to High- 
 cliff, which belong to the Bracklesham Beds, are the shore 
 deposits of the southern sea. The Bracklesham series 
 proper show a gradually deepening sea ; for, while the beds 
 of sand which are prevalent in the lower stages show 
 shallow water, the clay beds above them were formed in a 
 deeper sea, and contain deeper water mollusca. In compar- 
 ing the marine fauna with that of the London Clay, its very 
 much more tropical character is apparent. Many southern 
 types of mollusca abound in it which are scarcely repre- 
 
CHAP. XI.] HANTONIA1C PERIOD. 227 
 
 sented in the London Clay. Their aspect is completely 
 different, and though separated geologically by but a short 
 interval of time, hardly any species are common to both, 
 while the lithological characters of the formation are widely 
 and persistently dissimilar. If we examine, on the other 
 hand, the terrestrial fauna and flora of these and the 
 intervening strata, we see that no increase of temperature 
 or change had taken place in the climate, and that the land 
 was still inhabited by similar groups of reptiles and plants. 
 It is, therefore, plain that the sea alone had changed, and 
 become much warmer, for depressions had enabled the 
 southern sea, then occupying part of France, to advance 
 and to overlap to a small extent the older deposits." 
 
 Let us now turn to France and learn how this southern 
 sea came to reach so far northward. Professor Prestwich 
 and Mr. Gardner agree in thinking that the northern sea 
 of Lower Eocene times lay to the east and north-east of 
 our islands, and that the greater part of northern and 
 central France was land, this land being continuous across 
 the space between Brittany and Cornwall ; so that the 
 northern sea was entirely cut off from communication with 
 the warmer seas of more southern regions. The Lower 
 Eocenes of the Paris basin were formed in shallow bays 
 and lagoons on the northern border of this land, and their 
 fauna and flora are consequently those of the northern 
 province. 
 
 To the south of this Eocene France lay a wide and deep 
 sea which covered the greater part of southern Europe, 
 spread over the northern borders of Africa, and extended 
 far into the western part of Asia ; this sea was, in fact, a 
 greater Mediterranean, and in it were formed the Nummu- 
 litic limestones which occupy such large areas in the 
 regions above mentioned. 
 
 From the superposition of marine limestones upon the 
 1 <' Proc. Geol. Assoc.," vol. vi. pp. 95, 96. 
 
228 NEOZOIC TIME. [CHAP. XI. 
 
 lignitic series of the Paris basin, and the sudden appear- 
 ance in them and in their English equivalents of tropical 
 forms of mollusca, we may infer that a subsidence took place 
 which submerged part of the intervening land and allowed 
 the waters of the great Eocene Mediterranean to occupy a 
 portion of the low-lying tract on the northern side of the 
 barrier. The temperature was raised by this influx of 
 warm water, and a sub-tropical fauna and flora were 
 established on the shores of Britain. 
 
 In Mr. Gardner's opinion, however, this southern sea 
 never reached far into Britain. He thinks that its shore 
 must have lain across the north of Hants and Sussex, 
 while the area of the London basin was at this time part 
 of a tract of land which stretched eastward and formed a 
 barrier that prevented any commingling of the northern 
 and southern seas. In other words, he holds that the 
 depression of France coincided with a ridging up of land 
 over England and Belgium, so that the waters of the two 
 seas were still kept apart. He bases this opinion on the 
 distinctness of the Lower Bracklesham fauna, and in a 
 letter to the author has expressed himself as follows : 
 " I have carefully separated out the Lower Bracklesham 
 forms, and find an utter absence of any approaching to 
 the London Clay types. I am sure that the waters they 
 lived in were perfectly isolated from any of our older 
 Eocene seas." He therefore concludes that some barrier 
 must have existed to keep out the northern forms, for 
 otherwise there would have been a greater or less mingling 
 of the faunas, and he supposes this barrier to have been 
 submerged in Barton Clay times, when London Clay types 
 again make their appearance in Hampshire, and are mingled 
 with the remnant of the southern fauna. Mr. Gardner 
 informs me that the tropical forms of the Lower Brackles- 
 ham fauna disappear, a certain number, e.g., the great 
 Bulla, Cyprcea, and corals, dropping out rather suddenly, 
 
CHAP. XI.] HANTONIAN PERIOD. 229 
 
 others more gradually, while London Clay types modified 
 by time come in more and more. 
 
 It is certainly difficult to explain the peculiarities of the 
 Bracklesham and Parisian faunas on the supposition that 
 there was a complete and open communication between 
 the southern and northern seas, but on the other hand it 
 is not easy to indicate the exact location of the isthmus 
 which may be supposed to have separated them. The 
 Bruxellian deposits of Belgium, however, seem to throw 
 some light on the subject ; the majority of the Bruxellian 
 species are Bracklesham and Calcaire Grossier types, but 
 with these are associated a certain number of species which 
 are peculiar to the " Sables de Cuise," and have not yet 
 been found in the Calcaire Grossier of Paris ; l so that 
 there appears to be in Belgium just that very com- 
 mingling of the north and south faunas which does not 
 occur in England. It would seem, therefore, that there 
 was a direct communication between the French and 
 Belgian areas of deposition, and it is indeed certain that 
 such a connection existed during the formation of one 
 zone (z. de Nummulites Icevigata) at any rate ; for fragments 
 of hard sandstone with the fossils of this zone are scattered 
 at intervals over the axis of Artois, and most abundantly 
 over a tract to the south of Lille by Douai, Cambrai, and 
 St. Quentin, lying, like our Sarsen stones, sometimes on 
 the Lower Eocene sands, and sometimes on the Chalk, or 
 still older rocks. 
 
 Since, then, this zone extended completely across the 
 ridge, it is quite possible that the lower Bruxellian beds 
 did also, for the sandstone fragments have been preserved 
 in consequence of their hardness, and the fact of their 
 presence is no proof that the older beds did not have the 
 same extension. Professor Gosselet, therefore, is not 
 warranted in assuming, as he seems to have done in pre- 
 1 " Geologie de la Belgique," vol. i. p. 227. 
 
230 NEOZOIC TIME. [CHAP. XI. 
 
 paring his map of the Parisian epoch, 1 that no communica- 
 tion existed between the two basins except at the time of 
 the Numm. Icevigata zone. 
 
 Whatever conclusion may eventually be formed as to 
 the emergence or submergence of the axis of Artois during 
 the time of the Calcaire Grossier, it is very probable that 
 it and the Wealden area were upheaved at the close of 
 this epoch. 2 
 
 Such a view is confirmed to a certain extent by the close 
 correspondence which exists between the succession of the 
 higher Eocenes in the basins of London and Flanders ; 
 the " sables chamois " of the latter answer to our Upper 
 Bagshot Sands, and M. Ortlieb 3 thinks that these sands 
 were formed against the slopes of rising ground at the 
 time when the Upper Eocenes were being accumulated in 
 the Paris basin. The abundance of flint pebbles in the 
 Upper Bagshots also proves that Chalk was somewhere 
 exposed to erosion. 
 
 .It is possible, however, that the elevation was greatest 
 over the area of the Ardennes on the one hand, and over 
 the Wealden dome on the other, so that for a time the 
 two seas only communicated along the tract indicated by 
 Professor G-osselet. 
 
 However this may be, it is certain that central France 
 was raised above water at this time, and that the southern 
 sea was forced to retreat, so that the Anglo-French area 
 again became subsidiary to the northern province ; many 
 of the southern species of molluscs would be killed off by 
 the consequent refrigeration of the water, and their places 
 would be taken by northern species, and this seems almost 
 
 1 " Esquisse Geol. du Nord de France," p. 321, and PI. XIII. A. 
 
 3 Both Professor Hebert and Dr. Ch. Barrois are of this opinion : see 
 " Recherches sur les Terr. Cret. Sup.," by the latter, p. 1 78. 
 
 3 " Ann. Soc. Geol. du Nord," t. ii. p. 201 ; see also Barrois, t. iii. 
 p. 84. 
 
CHAP. XI.] HANTONIAN PERIOD. 231 
 
 sufficient to account for the difference between the faunas 
 of the Bracklesham and Barton Beds. 
 
 Oligocene Time. At the commencement of the Oligocene 
 period the geography of Britain can hardly have differed 
 much from that of the later Eocene time. England, Scot- 
 land, and Ireland still formed one united mass of land, 
 which was joined to France across what is now the western 
 opening of the English Channel, so that the Atlantic had 
 no communication with the area of the German Ocean. 
 The waters of the latter extended south-eastward through 
 Holland and over part of Belgium, but did not cover the 
 south of Belgium nor the south-east of England. 
 
 In the Anglo-French area the passage beds between the 
 Eocene and Oligocene show that the water in which they 
 were deposited became rapidly shallow, and the strong 
 unconformity between the two formations in Belgium 
 proves that this shallowing was mainly due to a general 
 upheaval of the whole of western Europe. 1 By this uplift 
 the sea spaces were contracted, and land connections were 
 formed with the African continent ; Europe was invaded 
 by a number of new terrestrial animals, and thus the 
 Oligocene is marked by the introduction of a new and 
 peculiar mammalian fauna, while the mollusca are obviously 
 the descendants of the species which inhabited the northern 
 province at the close of the Eocene period. 
 
 Let us now endeavour to restore the geographical out- 
 lines of southern Britain at this period. We may conclude 
 that the western part of the country, including the land 
 which then lay to the south of Ireland and united Corn- 
 wall to Brittany, was a region of hills and mountains, 
 among which at least one large river had its origin. This 
 river emptied itself into an estuary which lay at the north- 
 
 1 The principal upheaval of the Pyrenees is believed to have taken 
 place at this time. 
 
232 NEOZOIC TIME. [CHAP. xi. 
 
 western extremity of the sea or gulf which stretched from 
 the Paris basin into Hampshire (see map, Plate XII.). 
 
 The Headon Beds present us with a section through 
 part of the delta of this river. The alternation of marine, 
 brackish, and freshwater beds, is due, partly, to the pro- 
 cess of subsidence and silting up, partly, perhaps, to change 
 in the course of the river channel, but the northerly and 
 easterly increase of the marine strata (Brockenhurst Beds) 
 and the southerly increase of the freshwater limestones 
 are facts which prove the deepest part of the estuary to 
 have lain to the north-east of the Isle of Wight, and 
 to have trended from south-west to north-east through 
 Hampshire into Wilts or Somerset, in which direction the 
 embouchure of the great river probably lay. 
 
 The muddy flats of this estuary swarmed with Cerithiadce, 
 Cyrenidce, &c., while the pools of the delta were peopled by 
 species of Planorbis, Limncea, Paludina, &c., the dead 
 shells of which were swept down into the lower reaches of 
 the river ; crocodiles, gavials, and turtles abounded in its 
 waters as in those of modern tropical rivers, and its banks 
 seem to have been clothed with a luxuriant vegetation of 
 reeds, ferns, and palms. 
 
 The southern shore of the estuary lay probably at no 
 great distance from the Isle of Wight, and thence the 
 coast must have curved southward to Normandy, possibly 
 receiving the waters of another river from the south-west, 
 and from a direction parallel to that of the English Channel. 
 The southern shore-line of the Anglo-Parisian sea ran some- 
 where along the northern side of the watershed between 
 the Seine and the Loire, while the northern shore must 
 have skirted the southern slope of the Wealden area. 
 
 Similar conditions seem to have prevailed during the 
 formation of the Bembridge Beds, but Mr. Gardner thinks 
 that in these beds we have evidence, not only of a diminu- 
 tion in the volume of the river, accompanied by a general 
 
PLATE XII. GEOGRAPHY OF THE OLIGOCENE EPOCH. 
 
CHAP. XI.] HA.NTONIAN PERIOD. 233 
 
 silting up of the estuary and an increase in the area of the 
 delta, but also of a gradual lowering of the temperature ; 
 till at length, in the time of the Hempstead Beds, the vege- 
 tation ceased to have any specially tropical characters, and 
 the former estuary was converted into a swampy tract 
 covered with a growth of the rushes and water-plants that 
 belong to temperate climates. 1 
 
 With respect to the highest member of the Hempstead 
 group, Mr. Gardner remarks that the assemblage of marine 
 inollusca which it contains presents such a paucity of species, 
 and these so stunted in growth, as to suggest that the sea 
 which they inhabited had contracted to the dimensions of 
 a mere salt or brackish-water lake, without any communi- 
 cation with the open sea then lying over Belgium ; at the 
 same time, it is clear that at this period the depth of the 
 water in the Isle of Wight area was increased, not 
 diminished, and this must have been due either to sub- 
 sidence or to an influx of river-water into the lake. 
 
 When we consider that the whole of the British Oligo- 
 cene series consists of shallow- water deposits, it is evident 
 that a certain amount of subsidence must have taken place 
 during the period in order to allow of the accumulation of 
 such a thickness of beds (600 feet). That such subsidence 
 took place is proved also by the Belgian succession, and by 
 the comparatively deep-water character of the Argile de 
 Boom, which is generally regarded as the equivalent of 
 our Hempstead Beds. It is probable, however, that this 
 subsidence was more or less localized to the basins of de- 
 position, and it may have been contemporaneous with and 
 complementary to a rise of the Wealden axis. 
 
 The records of the Hampshire delta are here abruptly 
 broken off, and we have no means of ascertaining the last 
 phases of its history ; we can only guess from the analogy 
 
 1 " Proc. Geol. Assoc.," vol. vi. p. 98. 
 
234 NEOZOIC TIME. [CHAP. XT. 
 
 of the French deposits that there was a gradual upheaval 
 of the whole area, and that the depressions of this terres- 
 trial surface were occupied by large lakes. Whether any- 
 such lakes existed on British ground we do not know, but 
 many were scattered through the centre of Europe, in 
 France, Switzerland, Germany, and Austria. 
 
CHAPTEE XII. 
 
 ICENIAN PERIOD. 
 
 PHE reasons for grouping the Miocene, Pliocene, and 
 * Pleistocene deposits into one system have been given 
 elsewhere. 1 Their geographical extension is entirely diffe- 
 rent from that of the older (Hantonian) Tertiaries ; the 
 later Miocene and the older Pliocene deposits of the conti- 
 nent are so intimately connected that it is often difficult to 
 separate one from the other, while the close relations of the 
 Pliocene and Pleistocene are universally admitted. As, 
 however, the treatment of the Pleistocene epoch involves a 
 consideration of the Ice Age and the many debatable 
 questions connected with the Glacial deposits, it will be 
 more convenient to consider the geographical changes which 
 took place during the Miocene and Pliocene epochs first, 
 and to discuss the complicated phenomena of the Pleistocene 
 in a separate chapter. 
 
 1. Stratigraphical Evidence. 
 
 Miocene Epoch. Throughout both the Oligocene and 
 Miocene epochs the greater part of Britain remained in the 
 condition of dry land, and no actual Miocene deposits have 
 been found either in Britain or in the north-eastern part 
 of France. They occur in southern and western France, 
 and patches of them exist as far north as the Cotentin in 
 Normandy. Lately, also, it has been decided that certain 
 1 " Historical Geology,'' by the author, pp. 36 and 486. 
 
236 NEOZOIC TIME. [CHAP. XII. 
 
 deposits in Belgium are of Miocene age these are the 
 sands of Antwerp and the Bolderberg, which rest un- 
 conformably upon the Oligocene (Rupelien) clay, and have 
 a pebbly basement bed which contains flints and rolled 
 septaria ; the lower part of these sands is very dark and 
 argillaceous, and contains many shells in the position of 
 life ; the higher sands are less argillaceous, but still dark 
 coloured from the presence of glauconite, and the whole 
 group was formerly termed the " black crag." 
 
 There is some reason for thinking that similar deposits 
 originally extended across the North Sea into the east of 
 England, for the pebble beds at the base of the Suffolk 
 Crags contain nodules of greenish or reddish-brown sand- 
 stone, which enclose casts of some of the " black crag " 
 fossils. 1 Professor Ray Lankester has also recorded teeth 
 of a Mastodon whale and shark (Carcharodon) in the same 
 matrix, and he is of opinion that many of the mammalian 
 bones found in these nodule beds have been derived from 
 strata of Miocene age, of which no other traces now 
 remain. 
 
 Pliocene Epoch. The Pliocene series is divisible into an 
 older and a newer group, and the British beds of this age 
 may be classified as follows : 
 
 Newer. I Forest Bed Grou P- 
 
 ' ( Norwich and Red Crags. 
 
 f St. Erth Beds. 
 Older. < Coralline Crag. 
 I Lenham Sands. 
 
 The oldest Pliocene deposits in England are certain fer- 
 ruginous sands which at Lenham and other places on the 
 North Downs in Kent and Surrey are at or above the level of 
 600 feet. They were first described by Professor Prestwich 
 in 185 7, 2 and correctly referred by him to the Pliocene, but 
 
 1 Ray Lankester, " Quart. Journ. Geol. Soc.," vol. xxvi. p. 493. 
 
 2 " Quart. Journ. Geol. Soc.," vol. xiv. p. 322. 
 
CHAP. XII.] ICENIAN PERIOD. 23? 
 
 the imperfect nature of the fossils then found, and the 
 apparent presence of some Eocene species, led others to. 
 regard them as Lower Eocene. In 1886, however, Mr. 
 Clement Eeid was able to settle the question by obtaining 
 fresh specimens, which proved the beds to be of older Plio-. 
 cene age. The sands often contain flint pebbles, and include 
 layers of loamy clay and seams of fossiliferous ironstone, 
 and though their aspect is not that of deep-water deposits, 
 yet the perfect and unworn condition of the shells shows 
 that they are not shore deposits, and the fauna seems to. 
 indicate a depth of at least 20 fathoms. 
 
 The Lenham Sands occur at intervals along the Downs 
 from the heights above Folkestone to Chipstead, near 
 Croydon, 1 but though they are now found along this narrow 
 tract, it is evident that they are the remnants of a forma-L 
 tion which was once far to the north, and also some distance 
 to the south of this line. It would appear, in fact, that 
 though the upheaval of the Wealden area commenced in 
 Eocene times, and though this district was exposed ta 
 erosion throughout the times of the Tipper Eocene, Oligo-. 
 cene, and Miocene, yet that the great plane of denudation 
 out of which the present surface of the Weald is carved waa 
 formed by the waters of the early Pliocene sea. Conse-. 
 quently, if we would restore the surface over which the 
 Lenham Sands were laid down, we must imagine a sea- 
 floor stretching northward from the summit of the Chalk 
 escarpment at a high level above the Isle of Sheppey and 
 the estuary of the Thames. Fig. 6 is an attempt to restore 
 this horizon, and, allowing for some subsequent elevation 
 over the Wealden area, to show the position which the base 
 of the Lenham Sands would now occupy if they had not 
 been so largely removed by subsequent erosion. Over 
 
 1 At present, however, fossils haA'e only been found at Lenham, and 
 it is open to doubt whether the Chipstead sands, and those of Headley- 
 still further west, are precisely of the same age. 
 
CHAP. XII.] ICENIAN PERIOD. 239 
 
 Sheppey and Essex they doubtless rested on some member 
 of the Bagshot group, and thence their base-line passed 
 across the outcrops of the Lower Eocene and Cretaceous 
 strata till it rested on the Wealden beds over the central 
 axis of the Wealden area (see fig. 6). 
 
 Outliers of similar ferruginous sands occur also at inter- 
 vals in France and in southern Belgium, the level of their 
 base-line sinking lower and lower to the eastward. Thus, 
 at Cape Blanc-Nez, they are about 500 feet above the sea ; 
 at Cassel, near Ypres, their level is 470 feet ; above 
 Itenaix it is 445 ; at Gramont 380 ; on the heights above 
 Brussels it is only 245, and near Diest, though the level 
 varies considerably, their base nowhere rises above a height 
 of 200 feet. 1 Northward the base-line sinks still more 
 rapidly, and is less than 20 feet above the sea near Anvers 
 (Antwerp). Yet throughout this range the sands are simi- 
 lar in constitution and contents, proving that the present 
 differences of level are due to subsequent differential move- 
 ment of the land. Around Diest and Tessenderloo they 
 cover a large area, and attain a thickness of nearly 100 feet ; 
 at Antwerp they contain many fossils, and form the zone 
 of Isocardia cor, passing beneath newer Pliocene beds. 
 Northwards, as they pass beneath Holland, their thickness 
 increases, for at Utrecht a deep boring passed through the 
 overlying beds and 410 feet of Diestien Sand without 
 reaching their base, though carried to a depth of 1,208 feet. 
 The range of these beds in Belgium and the north of France 
 is shown in fig. 7, the eastern portion of which is reduced 
 from Vandenbroeck's map. 
 
 Returning to England, fine yellow sands, sandstones, 
 and sandy marls of somewhat similar character form the 
 lower division of what is known as the Coralline Crag in 
 Suffolk, and as nearly all the Lenham species occur also in 
 
 1 Vandenbroeck, " Bull. Soc. Beige Geol.," &c., tome i. p. 51, and 
 map. 
 
CHAP. XII.] ICENIAN PERIOD. 241 
 
 these sands, it is probable that they are nearly of the same 
 age, though possibly deposited in somewhat deeper water. 
 At their base is a pebble bed which contains the " box- 
 stones " already referred to, as well as rolled bones of 
 various mammalia, pebbles of flint and sandstone, blocks 
 of septaria from the London Clay, and at Sutton a large 
 boulder of dark red felstone. The overlying sands and 
 marls are from 20 to 50 feet thick ; they contain numerous 
 shells and Bryozoa, some in the position of life and growth, 
 others drifted and mingled with layers of comminuted 
 shells. 
 
 According to D'Orbigny the conditions essential to the 
 growth of Bryozoa are a considerable depth of water, clear 
 water, and the existence of strong currents ; the modern 
 species of Lepralia, for instance, of which many occur in the 
 Crag, are generally found between 40 and 150 fathoms. 1 
 Of the Corals one species lives now at depths of 10 to 60 
 fathoms, and the descendant of another (Fldbellum Woodii) 
 has only been found at depths of over 300 fathoms. The 
 Foraminifera, according to Messrs. Jones, Parker, and 
 Brady, agree best with the assemblage found between 50 
 and 70 fathoms off the Scilly Isles. 
 
 The sandy beds are overlain by the peculiar rock which 
 has given the name of Coralline Crag to the group ; this is 
 a soft, porous, yellow calcareous rock, which is almost en- 
 tirely composed of comminuted shells and Bryozoa ; it is 
 from 30 to 40 feet thick, and the irregular bedding and 
 oblique lamination which it exhibits are proofs of the action 
 of strong currents in drifting, sifting, and reconstructing 
 the layers of which it is composed. Mr. Prestwich con- 
 cludes, therefore, that this rock indicates shallower water 
 than that in which the sandy marls below were deposited, 
 and infers that during its formation the sea-floor was raised 
 
 Prestwich, " Quart. Journ. Geol. Soc.," vol. xxvii. p. 129. 
 
 J. J, t O L IT H.J.A ^ VU.t*A I* WUAU 
 
 R 
 
242 NEOZOIC TIME. [CHAP. XII. 
 
 by a movement of elevation and exposed to the action of 
 tidal currents. 
 
 The beds known as Coralline Crag are now limited to a 
 small area in Suffolk around and between the estuaries of 
 the Deben and the Aide, but they are evidently mere rem- 
 nants of a formation which had once a far wider extension. 
 
 The St. Erth Beds, which occur at a height of about 100 
 feet near Hayle in Cornwall, are regarded by Mr. C. Eeid 
 as approximately of the same age as the Coralline Crag. 
 They consist of fine clays and sands, in which many fossils 
 have been found, none of the shells having a northern 
 range, while some of them are southern species which have 
 not been found elsewhere in Britain. 
 
 Newer Pliocene. Coming now to the Newer Pliocene 
 series, we may consider the Bed and the Norwich Crags 
 together, as they are generally believed to be contempora- 
 neous deposits. The Red Crag of Suffolk rests either on 
 the London Clay or on an eroded surface of the Coralline 
 Crag, and it is surmised that the latter had been raised 
 into the condition of an actual land- surf ace and again sub- 
 merged before the deposition of the Bed Crag upon it. 
 The Norwich Crag rests chiefly upon the Chalk. 
 
 These newer crags underlie nearly the whole of eastern 
 Suffolk and Norfolk, extending westward as far as Sud- 
 bury in the former, and to Cringleford, near Norwich, in 
 the latter county. They, in turn, suffered much from 
 erosion at a later period, and we may assume that their 
 original boundary lay considerably to the west of their pre- 
 sent limits ; the probable position of this boundary and, 
 inferentially, of the sea in which they were deposited, is 
 indicated by the line B B, in fig. 7, p. 240. 
 
 The Bed Crag is divisible into two zones or stages : (1) 
 a lower set of shelly and current-bedded sands, largely 
 composed of the detritus of the Coralline Crag ; (2) an 
 upper set of horizontally stratified sands and clays (the 
 
CHAP. XII.] ICENIAX PERIOD. 243 
 
 Chillesford Beds) ; and it is believed that these Chillesford 
 Beds pass into the upper portion of the Norwich Crag. 
 Generally speaking, the Suffolk type is the more purely 
 marine deposit, and the Norwich Crag a more littoral 
 one. 
 
 The Sutton section described by Mr. Prestwich l is in- 
 teresting as affording definite evidence of subsidence during 
 the formation of the Eed Crag. This crag is here banked 
 up round an island of Coralline Crag, and two distinct 
 shelves or beaches are found, the upper one cutting into 
 the cliff at a height of 9 or 10 feet above the lower 
 one ; each beach has a basal bed of pebbles and phosphatic 
 nodules with large blocks of Coralline Crag derived from 
 the cliff above. A basement bed of this kind, but with- 
 out the blocks of Coralline Crag, is everywhere found at 
 the bottom of the Eed Crag, and yields chalk flints (some 
 very little worn), septaria from the London Clay, (Ter- 
 tiary) sandstones, Cretaceous chert, and fragments of red 
 granite. 
 
 The shelly sands above are from 10 to 30 feet thick, 
 and they have evidently been accumulated in shallow 
 water, the materials being largely derived from the erosion 
 of the older Tertiary deposits and heaped up by currents 
 into shoals and sandbanks, which have been shifted and 
 reconstructed many times before they came to rest in their 
 present position. 
 
 " The Norwich Crag," says Professor Prestwich, " which 
 occupies the contiguous area, and lies on the same level, 
 seems to have been divided from the more open sea of the 
 Bed Crag by a barrier of Coralline Crag, behind which 
 were sandy bays into which flowed a river or rivers, bring- 
 ing down land and freshwater shells, and probably the 
 mammalian remains, from land to the north-west and 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxvii. p. 340. 
 
244 NEOZOIC TIME. [CHAP. XII. 
 
 west. There is evidence of these streams coming from that 
 direction in the circumstance that in the Crag at Norwich, 
 Lias Ammonites, Mountain Limestone corals, besides the 
 many fossils from the Chalk, are found. I have found also 
 at the base of the Crag at Weybourn a fragment of fos- 
 siliferous Kimeridge Clay, and in the Norwich Crag a 
 fragment of an encrinital column similar to one I have 
 seen in the Red Crag of Sutton, in which latter also occur 
 Belemnites, Ammonites, Ostrece, and Terebratulce, from 
 various Secondary rocks, together with fragments of chert 
 from the Lower G-reensand, while the occurrence of the 
 fragments of red granite points to transport from still 
 more distant localities" (op. cit., p. 476). 
 
 The Chillesford sands and clays, and the laminated clays 
 which overlie the Norwich Crag, possibly indicate a further 
 submergence, for the sands are finer and less ferruginous, 
 the clays are grey and laminated, and the bivalve shells in 
 them frequently occur in undisturbed position with united 
 valves. At the same time there is a diminution in the 
 number of southern mollusca and a prevalence of northern 
 forms, facts which prove the waters to have become much 
 colder, and suggest that the quantity of ice in the Arctic 
 regions had greatly increased. 
 
 The Weybourn Crag mentioned above is of about the 
 same age as the Chillesford Beds, though possibly a little 
 newer, as in it Tellina balthica first appears, and the per- 
 centage of northern forms is increased to 16 per cent., that 
 of the Chillesford and Norwich beds being only 8 or 9 per 
 cent. 
 
 Shelly sands (Scaldisien of the Belgian geologists) simi- 
 lar to our Eed Crag cover a considerable area in the north 
 of Belgium, see map, fig. 7, and they extend northward 
 through Holland beneath the Pleistocene deposits of that 
 country ; in the deep boring recently made at Utrecht 
 their thickness was found to be no less than 270 feet, the 
 
CHAP. XII.] ICENIAN PERIOD. 245 
 
 Scaldisien sands being overlain by 528 feet of Pleistocene 
 deposits and underlain by over 400 feet of Older Pliocene 
 sands. 
 
 The highest and latest Pliocene beds known to occur on 
 the borders of the North Sea are those seen on the coast 
 of Norfolk, and known respectively as the Forest Bed and 
 the Leda myalls Bed. The so-called Forest Bed is really a 
 set of beds very variable in composition, comprising layers 
 of sand, gravel, clay, and lignite, with a total thickness of 
 10 to 20 feet ; they contain numerous drifted stumps and 
 branches of trees, with fir-cones and other plant remains, 
 bones and teeth of many mammalia, and estuarine inol- 
 lusca. Its upper surface, however, does in many places 
 present the appearance of an actual land surface, being 
 weathered into a soil and penetrated by rootlets ; here and 
 there also it is covered by lacustrine deposits containing 
 freshwater shells and bones of beavers, mice, moles, and 
 other small creatures. A rootlet bed similar to that of 
 Norfolk, and believed to be of the same age, occurs also at 
 Hopton, Gorton, and Kessingland in Suffolk, so that simi- 
 lar conditions appear to have prevailed over an area which 
 measured at least 40 or 50 miles from south to north. 
 They do not, however, extend far inland, and the neigh- 
 bourhood of Norwich appears to have been comparatively 
 high ground at the time of their formation. 1 
 
 The beds which underlie this terrestrial surface are clearly 
 such as would be formed in the estuary of a large river, 
 and it is therefore reasonable to regard the gravels and 
 sands as river-borne detritus, and to look to the pebbles 
 composing them as affording a guide to the direction from 
 which the river came. These pebbles have been carefully 
 studied by Mr. Clement Reid ; they consist chiefly of flints 
 and light-coloured quartzites, with other stones which seem 
 
 1 Clement Keid, " Geology of the Country around Cromer," p. 55. 
 
246 NEOZOIC TIME. [CHAP. XII. 
 
 to have been derived from Carboniferous, Lower Creta- 
 ceous, and Eocene rocks. There is a total absence of 
 Jurassic debris and of the liver-coloured quartzites which 
 are so common in the English Trias. " In fact," to quote 
 Mr. Reid, 1 " if the river had flowed from the south, west, 
 or north, it must have brought quite a different collection 
 of stones. From the north-east [had it come from that 
 direction] it would probably flow entirely over chalk. It 
 therefore seems that only from the south-east or east could 
 the stones be derived." This conclusion, as will be seen in 
 the sequel, is an important factor in the restoration of the 
 physical geography of the North Sea area at this particular 
 time. 
 
 Near Cromer these terrestrial deposits are succeeded by 
 the Leda myalis bed, which is from 4 to 15 feet thick, and 
 consists of fine loamy sand with marine shells, some of 
 them lying undisturbed in the position of life. It is clear, 
 therefore, that the last change which occurred in this por- 
 tion of the Pliocene area was a submergence which brought 
 in the sea once more over the lower parts of the newly- 
 formed land. This, however, seems to have been only a 
 temporary change, followed by an elevation of much greater 
 extent, during which the climate underwent an enormous 
 alteration. 
 
 2. Geographical Restoration. 
 
 Miocene Time. It will be remembered that the Oligocene 
 epoch was described as one of gradual upheaval, and as 
 closing with a general elevation of western Europe in 
 which the British region participated. That this continental 
 period lasted a long time is proved by the great change 
 which took place in the molluscan and mammalian fauna. 2 
 
 1 " Geology of Country around Cromer, Mem. Geol. Surv.," p. 56. 
 
 2 See "Historical Geology," p. 489. 
 
CHAP. XII.] ICENIAN PERIOD. 247 
 
 It was doubtless a period during which the action of rain 
 and rivers effected great changes on the surface of the 
 land, and it is possible that some of the geological features 
 of western and central England were initiated at this time. 
 By this expression I do not mean that the present physical 
 features of these districts were then developed, but that large 
 areas of Chalk and Eocene were then removed by erosion and 
 detrition from the borders of Wales and from the Midland 
 counties, and that the ridge or outline of the great Jurassic 
 escarpment may then have been developed, so that the 
 watershed between the valleys of the Severn and the 
 Thames may have been formed at this period ; but as the 
 recession of the Mesozoic escarpments was continued 
 throughout the Pliocene epoch, we must assume that in 
 Miocene times the escarpment of the Chalk lay much 
 nearer that of the Oolites than it does now, and that both 
 were to the westward of their present lines. The valley of 
 the Thames, as first pointed out by Sir A. Ramsay, must 
 be older than the development of the Chalk escarpment 
 through which it passes between Wallingf ord and Reading. 
 Its course must have been determined when the watershed 
 lay over the Jurassic escarpment, and when a sheet of 
 chalk covered by Eocene strata sloped away eastward from 
 the summit of the Cotteswold Hills. 
 
 From the position of the early Pliocene beds on the 
 North Downs overlooking the area of the Weald, we may 
 infer that the anticlinal dome or uplift of this area was 
 much less marked in Miocene time than it is now, and that 
 its central portion was not then relatively lower than the 
 tracts occupied by the Chalk, but that the whole area 
 formed a plateau of low elevation, from which perhaps the 
 Upper Cretaceous rocks had not yet been entirely removed. 
 The outer parts, and in all probability the tracts where 
 Upper Chalk is now at the surface, were then covered by 
 Eocene strata, and the greater part of what we call the 
 
248 NEOZOIC TIME. [CHAP. XII. 
 
 Weald may then have been occupied by broad plains of 
 Chalk marl and gault, with possibly a small central tract 
 of Lower Greensand and Weald Clay. We may at any 
 rate assume that the present drainage system of the Weald 
 was initiated at that stage in the history of its denudation 
 when such was the condition of its surface, though whether 
 this stage was reached in Miocene, or not until Pliocene 
 time, we are hardly yet in a position to determine. 
 
 From the facts mentioned on p. 235 we may conclude 
 that, after an interval of unknown duration, a general 
 subsidence at length took place, and the period marked by 
 the Miocene deposits commenced. This subsidence brought 
 the shores of a sea which opened southward within a 
 short distance of the British area, if it did not actually 
 invade it. On the south this sea reached to the Cotentin 
 district of Normandy, and on the east it stretched through 
 Belgium to the eastern shore of England. 
 
 Older Pliocene Time. The subsidence which had set in 
 during the formation of the Miocene beds seems to have 
 been continued during that of the older Pliocene, until the 
 whole of south-eastern England was submerged and the 
 sea covered districts which are now more than 600 feet 
 above its level. The remnants of the older Pliocene beds 
 are however so small and scanty, that it is difficult to draw 
 any trustworthy inferences from their distribution regarding 
 the probable limits of the sea in which they were formed. 
 
 The first point which calls for consideration is whether 
 there were two gulfs with an isthmus between them, as in 
 Miocene time, or whether the sea swept across the Channel 
 area and covered the whole of southern England. As re- 
 marked by Mr. Clement Eeid, 1 "a subsidence sufficient to 
 allow only 20 or 30 fathoms of water over the highest 
 parts of the North Downs would submerge the whole of 
 
 1 " Nature," Ang. 12, 1886, p. 342. 
 
CHAP. XII.] ICENIAX PEEIOD. 249 
 
 the east and south of England except a few hills," if it 
 were to be repeated at the present time. He points out, 
 however, that it is very unlikely that the relative levels and 
 contours of the Pliocene land were at all similar to those 
 of modern Europe, that it is much more probable that 
 subsequent differential movements have taken place, the 
 Wealden area having been upraised, while Holland was 
 depressed. 
 
 We may therefore start with the assumption that the 
 geography of early Pliocene time, so far as the relative 
 positions of land and sea in southern England are con- 
 cerned, did not bear much resemblance to that of the 
 present day, and, inversely, that we cannot use the modern 
 physical geography of the country as affording much 
 assistance in a restoration of the early Pliocene geography. 
 It is also certain that great changes took place in the in- 
 terval between the older and newer Pliocenes, and possibly 
 the geographical conditions of early Pliocene time re- 
 sembled those of the Miocene more than those of the later 
 Pliocene. It is true there was an eastern sea or German 
 Ocean which spread over a portion of southern England, 
 but there is no evidence that it approached our north- 
 eastern shores, neither is there any proof of the existence 
 of an English Channel. It is quite possible that England 
 was joined to France by land which united the Tertiary 
 and Cretaceous basin of Hampshire with those of northern 
 Prance, its southern border being perhaps a range of high 
 Chalk Downs, which extended south-eastward from the 
 Isle of "Wight and was continuous with the Chalk districts 
 of Normandy. It is conceivable that the Oligo-Miocene 
 upheaval had lifted this tract of country to a considerable 
 elevation above the sea, the rise being greatest over the 
 southern or Isle of Wight axis, but the whole country 
 sharing in the uplift. If this were so, the tract in question 
 would form an isthmus between the eastern and south- 
 
250 NEOZOIC TIME. [CHAP. XII- 
 
 western seas, and may never have been wholly submerged: 
 at any subsequent time. The limitation of the Lenham 
 and Diestian Sands to the northern side of this tract, and 
 their apparent absence over the South Downs, are facts- 
 which suggest that their original boundary line, and there- 
 fore the shore of the early Pliocene sea, lay somewhere over 
 the central axis of the Wealden district between the lines of 
 the North and South Downs, as shown in the map, fig. 7 r 
 where the line A A shows the supposed position of this 
 shore-line. 
 
 On the other side of the isthmus above mentioned lay 
 another sea, arms of which probably advanced into what i& 
 now the area of the English Channel. If Mr. C. Reid is 
 right in thinking that the St. Erth Beds belong to the 
 Older Pliocene epoch, a large part of Cornwall may then 
 have been covered by this southern sea, for, as Mr. Reid 
 observes, 1 " the St. Erth clay was evidently laid down in 
 still water, which would not be found at a less depth than 
 40 or 50 fathoms in a district exposed like this to the 
 Atlantic swells. The fossils also in that clay point to 
 some considerable depth of water, while the general 
 flattened contour of the country suggests that this district 
 has nearly all been submerged within a comparatively 
 recent period. The lower parts of Cornwall form a smooth 
 undulating country, out of which rise abruptly the higher 
 hills. Round one of these hills, St. Agnes' Beacon, coarse 
 sand is found at a high level. This is probably a beach 
 deposit of the same age as the clay at St. Erth, though all 
 fossils have now disappeared from it. Cornwall seems at 
 that period to have formed a scattered archipelago like the 
 Scilly Isles." 
 
 It must be admitted, however, that the separation of 
 these two seas is a doubtful question, and the mere absence 
 
 1 "Nature," Aug. 12, 1886, p. 342. 
 
CHAP. XII.] ICENIAN PERIOD. 251 
 
 of early Pliocene deposits from the intermediate area can- 
 not be held as a very serious objection to the view that 
 they communicated across the Hampshire basin. That the 
 Diestian or Coralline Crag sea had some very direct com- 
 munication with the Mediterranean and west European 
 area is indicated by the large proportion of Mediterranean 
 species among its mollusca, namely 200 out of the 265 
 living species, or 75 per cent., 17 of them being now con- 
 fined to the southern area ; it is difficult to see in which 
 direction this connection could have existed if not through 
 England and France. 
 
 It is generally supposed that the Anglo-Belgian sea of 
 this period opened northward into the Arctic Ocean, but 
 this belief is doubtless founded upon the present extension 
 of the German Ocean, which is really more likely to have 
 been initiated in the later part of what we call Pliocene 
 time. I cannot find, indeed, that there is any good reason 
 for supposing the sea of the Coralline Crag to have stretched 
 far north of Suffolk. In fact, the total absence of any signs 
 of Coralline Crag or of the box-stones in Norfolk, and the 
 manner in which the lower and older portions of the newer 
 crags thin out northward and westward in that county, 
 are significant facts which incline me to believe that Nor- 
 folk at any rate did not form part of the early Pliocene sea- 
 floor ; in other words, that the Coralline Crag was deposited 
 in a gulf which lay wholly to the south of Norfolk, and 
 was limited by a promontory of land which stretched out 
 north-eastward from Norfolk far into what is now the North 
 Sea, if it did not reach entirely across to the shores of 
 Norway and form a complete barrier between the Anglo- 
 Belgian sea and the Arctic Ocean. 
 
 The mere presence of some twelve or fourteen species 
 which have now a northern, i.e. Arctic or Scandinavian, 
 habitat, cannot be taken as proof that there was any con- 
 nection with the Arctic sea, for these species may then have 
 
252 NEOZOIC TIME. [CHAP. XII. 
 
 been British and Belgian forms which, at a subsequent 
 period, when, circumstances permitted, ranged northward 
 and found a lower temperature more congenial. We do 
 not know how many species of the Pliocene mollusca were 
 forced by the increasing cold of the Glacial period to adapt 
 themselves to a cold climate ; some probably would do so, 
 while others were exterminated or driven to more southern 
 climes. Neither does the transportal of the f elstone boulder 
 of Sudbourn, even if accomplished by ice, involve the influx 
 of a current from Arctic regions. 
 
 All these questions will doubtless be ably discussed by 
 Mr. Clement Eeid in the monograph on the British Plio- 
 cene Deposits which he has in preparation, and it would be 
 both premature and presumptuous if I were to attempt a 
 solution of so difficult a problem in the present volume. 
 Before dismissing the subject, however, attention may be 
 called to the opinions formed by Messrs. Kendall and Bell 
 from a study of the St. Erth fossils, with regard to the 
 geographical connections of the sea in which they lived. 
 From the prevalence of Mediterranean species they infer a 
 direct communication with that sea through Normandy 
 and the south-west of France ; while from the absence of 
 Arctic species they are led to think that the Arctic Ocean did 
 not then open into the Atlantic, but that the land commu- 
 nication which is believed to have existed between Europe 
 and North America in Eocene times, by way of Iceland 
 and Greenland (see p. 215), continued to exist through the 
 Miocene and early Pliocene epochs, so as to form a barrier 
 of separation between the Arctic and Atlantic oceans. 
 
 They point out that 1 a submerged ridge, covered by less 
 than 350 fathoms of water, but with deep water on either 
 side of it, extends from Scotland to the Faroe Isles, and 
 has had, as explained by the late Dr. Jeffreys, a great in- 
 fluence in preventing the intermingling of the marine 
 1 '' Qunrt. Journ. Geol. Soc.," vol. xlii. p. 207. 
 
CHAP. XII.] ICENIAN PERIOD. 253 
 
 faunas on each side of it. " From the Faroes to Iceland 
 an undulating bottom exists, reaching a depth of 368 
 fathoms, whence a plunge takes place to 686 fathoms, and 
 within 30 miles recovers to 350 fathoms. Across the Den- 
 mark Straits, between Iceland and Eastern Greenland, the 
 depth nowhere reaches 500 fathoms." 
 
 If this tract of comparatively shallow water were land, 
 as it is believed to have been in Miocene and Eocene times, 
 and if Greenland was then united to America, as is most 
 probable, no Arctic currents could have entered the Atlan-* 
 tic Ocean, and the climate of its northern shores would be 
 much milder than at present. Under such geographical 
 conditions Greenland and Iceland may have been fitted to 
 support a luxuriant flora, as they undoubtedly did in 
 Eocene times ; for Dr. A. E. Wallace observes that " the 
 existence at the present time of an ice-clad Greenland is 
 an anomaly in the northern hemisphere, and only to be ex- 
 plained by the fact that cold currents from the polar seas, 
 flow down both sides of it." 1 
 
 Newer Pliocene Time. From the general relations of the 
 newer to the older Pliocene beds we may conclude that an 
 upheaval of considerable extent took place at the close of 
 the older epoch, and that these older deposits (Coralline- 
 Crag, &c.) were raised into the condition of dry land. The 
 present position of the Lenham Sands shows that the up- 
 lift was greatest over the Wealden area, while Suffolk was. 
 either never raised to such an elevation, or was subse-. 
 quently depressed to a much greater extent. We may 
 safely say that the waters of the Diestian Sea were entirely 
 displaced from the British, French, and Belgian areas for 
 a certain length of time, and that these three countries 
 were united into one broad, mass of land, which stretched 
 northward to Iceland and Greenland, as heretofore through* 
 out the Tertiary era. 
 
 1 Island Life," 1880, p. 149. 
 
254 NEOZOIC TIME. [CHAP. xii. 
 
 This general elevation was followed by a local and partial 
 subsidence, limited apparently to what is now the North 
 Sea and its borders. This subsidence allowed the waters 
 of an eastern sea once more to invade English territory, 
 and eventually opened up a communication between this 
 sea and the Arctic Ocean. 
 
 It is highly probable that it was the movement that 
 led to the formation of the North Sea which gave the 
 easterly dip to the Eocene and Cretaceous rocks of eastern 
 England and an easterly tilt to the whole London Basin ; 
 it is certain, at any rate, that any slight easterly dip which 
 they may previously have had was at this time greatly in- 
 creased. We have seen that the geography of the older 
 Pliocene epoch bore little resemblance to that of modern 
 England, and though some of our Midland hills and valleys 
 may date from Miocene times, yet it is probable that the 
 development of the Cretaceous escarpments and of the corre- 
 sponding longitudinal valleys, as well as the trenching of 
 these escarpments by certain of our rivers, was accomplished 
 during the period we are now discussing. 
 
 That the close of the Pliocene epoch found the main 
 physical features of England fully developed, and the 
 Mesozoic escarpments occupying their present positions, we 
 know from the relations of the Pleistocene (Grlacial) de- 
 posits to these features. We may, therefore, fairly infer 
 that, though the rivers which flow eastward and cut through 
 the great Chalk escarpment may have first established their 
 channels at an earlier epoch, yet it was the easterly tilting 
 of the country at this time which gave them the power of 
 excavating their present valleys in such a comparatively 
 short space of time, and which enabled their tributaries to 
 remove such large areas of Eocene and Chalk. We must 
 remember, also, that this process of erosion and denudation 
 would proceed contemporaneously with the formation and 
 recession of this Chalk escarpment. I am, therefore, in- 
 
-CHAP. XII.] ICENIAN PERIOD. 255 
 
 dined to believe that all the great gaps which exist in this 
 escarpment, those of the Thames Valley, the Wash, and 
 the Humber, date from Pliocene times, and are, there- 
 fore, pre-G-lacial. Let us see how the evidence of the 
 newer Crags and their contents fits in with this theory. 
 
 Professor Prestwich has shown that the Red Crag was 
 accumulated in a shallow sea studded with reefs of the 
 Coralline Crag, round which set strong and shifting cur- 
 rents. " The direction of the currents, judging from the 
 nature of the foreign materials found in the Red Crag, 
 seems to have been from the west to the south-east." l He 
 thinks the occurrence of unrolled flints and of large blocks 
 of Coralline Crag indicate transportal by shore-ice, but this, 
 I think, is hardly likely ; the blocks of Crag are only de- 
 scribed as occurring near the cliffs from which they were 
 quarried, and ordinary wave-action is sufficient to account 
 for such limited dispersal. Neither does the presence of un- 
 rolled flints really necessitate the existence of shore- ice ; 
 they may have been carried by uprooted trees borne to sea 
 by rivers in time of flood, or by ground-ice formed in the 
 same rivers during severe winters. 
 
 Speaking of the Norwich Crag Mr. H. B. Woodward 
 remarks, " A study of the subject in conjunction with the 
 Suffolk Crag leads to the suggestion that the area was 
 gradually being depressed, and that the land to the nortli 
 was being slowly submerged, so that the Chalk cliffs which 
 then formed the coast-line were gradually destroyed north- 
 wards and westwards, and the neighbourhood of Norwich 
 came within the influence of the Crag sea before that of the 
 Bure valley. This gradual submergence perhaps led to 
 the introduction of Tellina balthica by the opening up of a 
 connection with some previously distinct area." 2 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxvii. p. 354. 
 
 2 "Geology of the Country around Norwich," Geol. Surv. Mem., 
 p. 37. 
 
256 NEOZOIC TIME. [CHAP. XII. 
 
 The contents of the Norwich Crag (see p. 244) plainly 
 show that the rivers which entered the shallow sea came 
 from the westward and carried debris which had been 
 derived from the central parts of England. From the great 
 depth of the Crag at Southwold (147 feet), and at Beccles 1 
 (80 feet), where the muddy nature of the deposits is also 
 remarkable, we might suppose that one of these rivers 
 traversed what is now the valley of the Waveney, this 
 being continued westward into that of the Little Ouse, 
 which may then have been occupied by a river coming from 
 the region of Bedford and Bucks, where the Ouse now 
 takes its rise. This stream, however, could hardly have 
 carried the Carboniferous fossils which have been found in 
 the Crag, and unless these were drifted along the coast 
 from some far northern locality, Derbyshire and Leicester- 
 shire are the nearest and most probable sources. The 
 valley of the Trent at once suggests itself as a possible 
 channel of transport, for we know that the ancient course 
 of this river was not that which it now follows, but through 
 the Jurassic escarpment along the valley now occupied by 
 the Witham into the basin of the Wash. 2 Further, its 
 drainage system is such that its tributaries could derive 
 all the stones which have been recorded as occurring in the 
 Norwich Crag. 
 
 Bearing in mind these facts and the general considera- 
 tions mentioned on p. 254, there is nothing improbable in 
 the suggestion that the breach in the Chalk escarpment 
 which is now occupied by the Wash was initiated by the 
 combined forces of the rivers Trent, Witham, Welland r 
 and Nen, before this escarpment had receded to anything 
 like its present position. There is every reason to suppose 
 that in later Pliocene time all these rivers traversed the 
 
 1 Woodward, " Geology of the Country around Norwich," p. 156. 
 
 2 See " Quart. Journ. Geol. Soc.," vol. xxxix. p. 606, and " Geology 
 of the Country around Lincoln," Mem. GeoJ. Survey. 
 
CHAP. XII.] ICENIAN PERIOD. 257 
 
 Jurassic ridge, although only two of them (the Welland 
 and Nen) now retain their ancient channels, and we may 
 fairly assume that the bay of the Wash did not then exist, 
 but that the combined streams of the above-mentioned 
 rivers occupied a broad valley which passed along or just 
 outside the northern coast of Norfolk, and opened into an 
 estuary somewhere to the north-east of that county (see 
 Plate XIII.). That a river of some size did at a much later 
 date pursue such a course has been surmised from the 
 peculiar geological features presented by the northern coast 
 of Norfolk. This coast is bordered by a continuous strip 
 of alluvium, the western part of which rests on boulder- 
 clay which is banked against a steep slope of chalk. 
 Kef erring to the alluvium, Mr. H. B. "Woodward remarks, 1 
 " the physical characteristics of the area suggest that this 
 low ground was originally an old river- valley, and that the 
 heights which bordered it on the north have been destroyed 
 by the ravages of the sea." 
 
 Passing now from these details of the Pliocene river- 
 system, let us consider what other changes may have been 
 caused by the depression which led to the formation of the 
 North Sea. The most direct and important change was 
 the submergence of the land which had hitherto from 
 the commencement of Tertiary time united Scandinavia 
 with Scotland and Iceland. Not only did this depression 
 open a communication with the Arctic Ocean, but in all 
 probability with the North Atlantic also, by the temporary 
 breaching of the isthmus between Scotland and the Faroe 
 Islands, and by the conversion of the deep valley or hollow 
 north of these islands into a strait. By these passages 
 many North Atlantic and American species of mollusca 
 gained access to the Anglo-Belgian part of the Pliocene 
 Sea, no fewer than eighteen American species occurring in 
 
 1 " Geology of the Country around Fakenham," Geol. Surv. Mem. , 
 p. 44. 
 
258 NEOZOIC TIME. [CHAP. XII. 
 
 the newer Crags, only seven of which still live on the 
 Scandinavian coast, the remainder being now confined to 
 the North American region. 
 
 This view of late Pliocene geography is represented on 
 Plate XIII., and this differs from previous restorations 
 chiefly in those particulars where recent information has 
 afforded more correct data than were formerly available. 
 The first attempt to give an outline of Pliocene geography 
 -was by Mr. God win -Austen, who, in 1866, 1 published a 
 map on which the supposed area of " the Crag Sea " was 
 delineated. At that time, however, it was unknown that 
 the sands of the Coralline Crag ranged so far south and 
 to such a high level ; while many deposits were then called 
 Crag which have since been proved to be of Pleistocene age ; 
 consequently, his map combines portions of the geogra- 
 phical conditions of several distinct periods, and is not 
 correct for any one portion of them. 
 
 Professor Boyd Pawkins has given a map of Pliocene 
 Britain 2 which may be taken as an approximation to that 
 of the later portion of the period, but since its publication 
 Mr. Jamieson has shown that the supposed Crag of Aber- 
 deen is a remanie deposit of Pleistocene age, 3 and conse- 
 quently there is no proof of the Eed Crag sea having 
 touched any part of the Scottish coast. In the region of 
 the Faroe Islands, also, Professor Dawkins shows a greater 
 area of water than I deem probable ; for it should be re- 
 membered that the whole of the newly-formed North Sea 
 may have been very shallow. No deep-sea deposits of 
 Pliocene age have yet been found in north-western Europe, 
 and the phenomena of the Forest Bed show that a very 
 slight upheaval was sufficient to convert a large area of it 
 into dry land. 
 
 1 " Quart. Journ. Geol. Soc.," vol. xxii. p. 240. 
 
 2 Early Man in Britain," 1880, p. 73. 
 
 3 " Quart. Journ. Geol. Soc.," 1882, vol. xxxviii. p. 145. 
 
PLATE XIII. GEOGRAPHY OF THE NEWER PLIOCENE EPOCH. 
 The closer lines representing sea-areas at the time of the Forest Bed. 
 
CHAP. XII.] ICENIAN PERIOD. 259 
 
 In fact, at the time of the Cromer and Kessingland 
 " rootlet bed," it is probable that much of the southern 
 part of the North Sea area passed into the condition of a 
 broad plain of dry land studded with large shallow lakes, 
 like the " broads " of modern Norfolk. Such is the opinion 
 which Mr. C. Reid was led to form from a study of the 
 Forest Bed and its associated deposits ; and the follow- 
 ing remarks are quoted from his memoir : l " The large 
 number of mammals already known from the Forest Bed 
 seems clearly to point to a connection with the conti- 
 nent ; " but " both the fauna and flora, leaving out the 
 large mammals and other extinct forms, are curiously like 
 that of the ' broad ' district of Norfolk at the present day ; 
 and this, like the rest of the evidence, points to a wide 
 alluvial plain with lakes and sluggish streams, bounded 
 on the west by a slightly higher sandy country covered with 
 fir-forests and distant from any hills." 
 
 It is supposed that this plain was traversed by a large 
 river coming from the south-east, as stated on p. 246, and 
 that this river was no other than a continuation of the 
 Rhine ; a view first suggested by Mr. Gunn in 1867, but 
 adopted and strengthened by subsequent writers. Thus 
 Professor Prestwich, writing in 1871, remarks that on the 
 table-land above the Meuse in Belgium there is a gravel of 
 very similar character, and though, according to Mr. C. Reid, 
 this contains veined quartzites of a character unknown in the 
 Forest Bed gravels, yet the general similarity of the gravels 
 suggests that they belong to one and the same system of 
 drainage. Mr. Reid himself suggests that the fragments of 
 Carboniferous slate and chert may have been derived from 
 rocks that " came to the surface as part of the old ridge 
 which Mr. Godwin- Austen has described," and as the 
 Ardennes are part of this ridge, it is difficult to see why he 
 should have any hesitation in assenting to Professor Prest- 
 1 " Geology of the Neighbourhood of Cromer," pp. 60, 61. 
 
260 NEOZOIC TIME. [CHAP. XII. 
 
 wich's view : the Meuse was then in all probability a tribu- 
 tary of the Rhine, and it is to the Rhine itself that Mr. 
 Reid refers the transport of the pebbles in question. In 
 his memoir on the neighbourhood of Cromer Mr. Reid has 
 given a sketch-map representing the probable position of the 
 estuary of the Rhine during the formation of the Forest Bed. 
 This is reproduced with slight alterations in Plate XIII., 
 the limits of the sea at the close of the Pliocene epoch 
 being shown by the boundary of the darker tint. It is 
 assumed that the whole area of the North Sea was greatly 
 contracted by upheaval from its previous extent, though 
 whether this elevation included the Scoto-Icelandic area, 
 and was sufficient to raise the connecting isthmus once 
 more above the sea, is doubtful, but such a connection is 
 shown on Plate XIII. because it is suggested in the sequel 
 that a further elevation to this extent did supervene in 
 the interval between the Pliocene and Pleistocene epochs. 
 
CHAPTER XIII. 
 ICENIAN PERIOD. 
 
 PLEISTOCENE EPOCH. 
 
 E a detailed account of the deposits of this period I 
 must refer the reader to my previous volume on " His- 
 torical Geology," and to Mr. H. B. Woodward's " Geology 
 of England and Wales." For my present purpose it is only 
 necessary to give such a summary of what is known re- 
 specting the distribution and succession of these deposits 
 in England, Ireland, and Scotland as may afford a basis 
 for considering the physical and geographical changes which 
 took place during the period. 
 
 The Pleistocene deposits are generally treated under the 
 heads of Glacial and Post-glacial Beds by British writers, 
 but, though this is a convenient division in dealing with 
 the deposits of a limited area, it becomes misleading when 
 those of a larger region are compared with one another, as 
 for instance those of southern and northern England. The 
 so-called Ice Age or Glacial Period must be regarded as a 
 special episode or phase of Pleistocene time, and though its 
 influence may be traceable over a large area of the earth's 
 surface, yet the deposits which owe their origin to the 
 direct action of ice are limited to certain regions within the 
 40th parallels of latitude in both hemispheres. 
 
 There is no doubt that what took place in the Glacial 
 period was simply an extension of the glacial conditions 
 which now exist in the polar regions. The fauna of the 
 Pliocene Beds affords evidence of the gradual refrigeration 
 
262 NEOZOIC TIME. [CHAP. XIII. 
 
 of the climate in that period, and there can be little doubt 
 that glacial conditions prevailed in high northern regions 
 while the Crags were being formed in the east of England. 
 The ice must have been creeping southward for a long 
 time before it reached the latitude of Norfolk and led to 
 the formation of the remarkable accumulations which suc- 
 ceed the Pliocene beds of that district. Again, it is cer- 
 tain that ice lingered in Scotland, and in the mountain dis- 
 tricts of England and Ireland, long after it had disappeared 
 from the southern part of our country. 
 
 1. Stratigraphical Evidence. 
 
 In our review of the Pleistocene period it will therefore 
 be best to consider the whole succession of deposits which 
 occur in different parts of our islands consecutively, so far 
 as that succession has been ascertained. 
 
 Scotland. 
 
 Glacial Deposits. Many attempts have been made to 
 classify the Boulder-clays and gravels of Scotland, but no 
 two writers seem to be quite agreed as to the precise se- 
 quence ; some still speak of the Boulder-clay of Scotland, 
 as if there were only one, and others are willing to believe 
 in any number of such clays if only they are separated by 
 fossiliferous sands or gravels. Mr. Jamieson, however, has 
 shown that there are at least two distinct Boulder-clays, 1 
 and from Professor James G-eikie's descriptions 2 we may 
 infer that there are at least three sets of Glacial deposits. 
 The oldest are Boulder-clays of the hard and compact kind 
 which is locally known as Till; the stones which they 
 
 1 "Quart. Journ. Geol. Soc.," vol. xxi. p. 162, and vol. xxxviii. 
 p. 160. 
 
 2 ' Prehistoric Europe," pp. 261 and 386 ; " Great Ice Age," second 
 edition, p. 216. 
 

 CHAP. XIII.] PLEISTOCENE EPOCH. 263 
 
 contain show that the ice under which they were formed 
 radiated outwards from the main watersheds of the country, 
 and they do not contain any intercalated marine deposits. 
 Elsewhere, as in Lewis, Caithness, Aberdeen, Arran, and 
 the central Lowlands, there are Boulder-clays which contain 
 broken sea-shells and include sands and gravels of marine 
 origin ; these deposits have not yet been found for certain 
 much above 500 feet, but Mr. Jamieson has described stra- 
 tified drifts occurring at a much greater height. Lastly, 
 there is a set of stratified deposits (soft sands, gravels, and 
 clays) which contain some Arctic species of shells, but do 
 not occur above the 100-feet contour line, and pass into 
 ancient river-gravels above that level. These last appear 
 to have been contemporaneous with the kames or eskers, 
 and with the moraines of the later glaciers in the Highland 
 valleys. 
 
 This succession of deposits is particularly clear in Aber- 
 deenshire, where, resting on a rock-surface that is glaciated 
 from west to east, lies a tough grey Boulder-clay containing 
 stones which have clearly been brought from western loca- 
 lities, or derived from the rocks in the neighbourhood. 
 This clay varies greatly in thickness, as if it had suffered 
 from subsequent erosion, and is sometimes reduced to a 
 layer of grey rubbish and boulders. Above this, or in its 
 absence resting on a rock- surf ace that is glaciated from the 
 south and S.S.W., is a red Boulder-clay containing stones 
 which have come from localities to the southward. This 
 clay is sometimes as much as 100 feet thick, and it is asso- 
 ciated with sands and gravels which contain broken marine 
 shells ; it ascends to a level of 300 feet above the sea, and 
 gravelly deposits containing similar stones occur up to 500 
 feet. Lastly, by the estuaries of the Tay and the Earn, there 
 is a mass of stratified drift, the upper surface of which is 
 almost flat and is about 100 feet above the sea ; it main- 
 tains this level all the way from the coast to Dalreoch in 
 
264 NEOZOIC TIME. [CHAP. XIII. 
 
 the valley of the Earn, and to Luncarty, above Perth, in 
 that of the Tay, passing ultimately into gravels of tor- 
 rential origin, which descend from the valleys of the Gram- 
 pian Hills. To the same stage belong the fossiliferous 
 brick-clays of the Forth and Clyde valleys. 
 
 Post-Glacial Deposits. These consist of raised beaches 
 and clay-flats lying between low-water mark and the con- 
 tour of 50 feet above mean sea-level. The most important 
 and widely distributed deposit is that known as the 
 Carse-clay, or the estuarine clay which forms the elevated 
 alluvial levels which are known as Carse-lands. The 
 surface of these levels near the sea-bord is from 25 
 to 30 feet above the sea, and their borders coincide 
 with a line of raised sea-beach at the same level. When 
 traced inland up the valleys their surface rises gra- 
 dually to a level of about 45 or 50 feet, at which level 
 they pass into freshwater alluvium, while their lateral 
 portions thin off against the raised beach, which occupies 
 the 50-foot contour. The clays and silts contain marine 
 shells, of which Scrobicularia piperata is one of the com- 
 monest ; but at or near the base there is frequently a bed 
 of peat in which trunks and rooted stools of trees occur, 
 and in some places this peat bed passes below the mean 
 level of the sea and is then called a submarine forest-bed. 
 The modern river- valley is excavated through the Carse- 
 clays, and contains fluviatile deposits of the ordinary 
 recent freshwater type. 
 
 In some cases, as in that of the Tay, 1 there are river- 
 gravels beneath the Peat and Carse-clay, and these, as well 
 as the submarine extension of the Peat, show that the land 
 stood at a higher level and had a farther seaward exten- 
 sion than it has now. The Carse-clay marks a period 
 
 1 J. Geikie in " Prehistoric Europe," p. 316, and Jamieson. " Quart. 
 Journ. Geol. Soc.," vol. xxi. p. 184. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 265 
 
 of subsidence, and the modern river-gravels one of 
 emergence. 
 
 England and Wales. 
 
 Glacial Deposits. In the mountain districts, as in Scot- 
 land, there are traces of Boulder-clays and morainic de- 
 posits which contain local debris and have other special 
 characters, and sometimes these are seen to pass beneath 
 newer clays which contain far-travelled boulders and are 
 associated with sands containing marine shells. These two 
 sets of Glacial deposits are well developed in Lancashire, 
 Cheshire, and North Wales, and their differences have been 
 described by Mr. Mellard Eeade 1 and Mr. A. Strahan. 2 
 
 So long ago as 1852 Sir Andrew Ramsay showed that 
 in North Wales there had been an early glaciation by 
 glaciers, followed by a submergence of at least 1,400 and 
 probably of 2,000 feet, and that when the land again 
 emerged from the sea it was once more occupied by a sys- 
 tem of glaciers which have left their terminal moraines in 
 many of the valleys. The proofs of submergence consist 
 in the existence of stratified marine deposits at high levels ; 
 thus, on Moel Tryfaen in Carnarvonshire there are sands 
 and gravels containing shells and overlain by Boulder-clay 
 at a level of 1,350 feet. Most of the stones and boulders 
 are of local rocks, but among them are pieces of granite 
 from Eskdale in Cumberland, and flints probably derived 
 from the Chalk of Ireland. In the county of Flint, between 
 levels of 1,100 and 1,250 feet, there are gravels contain- 
 ing broken shells and erratics which have come from the 
 Snowdon and Arenig ranges to the eastward, while close 
 by are trains of boulders which have come from the north- 
 ward. What relation these deposits bear to the low-level 
 
 1 " Quart. Journ. Geol. SOP.," vol. xxxix. p. 83. 
 
 2 Ibid., vol. xlii. p. 369. 
 
266 NEOZOIC TIME. [CHAP. XIII. 
 
 marine drifts which spread over so large a part of Che- 
 shire and Lancashire has not yet been ascertained, but 
 high-level marine beds have been found at a height of 
 1,200 feet near Macclesfield. 
 
 In the midland and eastern counties, also, two distinct 
 groups of Glacial deposits are found. The older group is 
 well developed in East Anglia, and it is generally supposed 
 that the oldest Pleistocene beds in England are those which 
 succeed the Pliocene series near Croraer. These consist of 
 laminated clays, sands, and boulder-clays, overlain by a 
 mass of contorted loam, sand, and gravel, the whole at- 
 taining a thickness of nearly 200 feet, and yielding shells 
 of marine species ; these beds are believed to pass inland 
 beneath the grey or chalky Boulder-clay which has such a 
 wide extension to the south, west, and north-west. Some 
 doubts indeed have recently been thrown on this presumed 
 succession, 1 but the difficulties experienced in the mapping 
 of north-east Norfolk can hardly be allowed to invalidate 
 the succession which holds good over such large areas to 
 the southward, where the deposits are less disturbed and 
 contorted ; it may, in fact, be stated that throughout Essex, 
 Herts, Suffolk, and south Norfolk, except where the height 
 of the ground rises above 300 feet, there is a lower set of 
 loams, clays, sands, and gravels, which sometimes contain 
 fragments of marine shells, and are overlain by a chalky 
 Boulder-clay which is quite destitute of such remains. 
 Beyond these counties there is no such definite succession, 
 but the upper Boulder- clay spreads over large areas to the 
 westward and is associated with irregular masses of sand 
 and gravel. 
 
 There are certain facts connected with the surface eleva- 
 tion of the eastern parts of Norfolk and Suffolk, and with 
 the distribution of the chalky Boulder-clay, which are 
 
 1 Reid, "Geology of the Country around Cromer," p. 115, and 
 Woodward, " Geology of the Country around Fakenham," &c., p. 19. 
 

 CHAP. XIII.] PLEISTOCENE EPOCH. 267 
 
 very striking and suggestive. From Hunstanton and 
 Burnhani to the latitude of Bury St. Edmunds, the whole 
 country presents the appearance of having been planed 
 down by some powerful agency. No part of the surface 
 rises above the level of 270 feet, and the greater portion is 
 much lower. The slopes of the Chalk hills do not present 
 the bold features which they possess in Cambridgeshire, 
 and there is no continuous ridge which could be dignified 
 with the name of an escarpment, that feature only really 
 commencing with the hills south-east of Newmarket. The 
 height of these latter hills is nearly 400 feet, and south of 
 the Cam Valley the escarpment rises to more than 500 
 feet. It is true that the Boulder-clay climbs these slopes, 
 but it dies out on the heights above Hitchin, at a level of 
 about 550 feet, giving place to loams which have been 
 formed from the material of the clays and sands of the 
 Reading Beds, and are often merely reconstructed plastic 
 clay, just as the chalky clay is often only reconstructed 
 chalk. At lower levels, however, the typical chalky 
 Boulder-clay continues much farther south, extending 
 through Herts and into Middlesex as far as Finchley, and 
 on the western side of the Chiltern Hills to the neighbour- 
 hood of Aylesbury and Buckingham. 
 
 How far to the westward this clay originally extended we 
 do not yet know, but no trace of it has been found beyond the 
 limits of a line drawn through the central parts of Oxford- 
 shire, Warwickshire, and Staffordshire. Northward the 
 clay is known to extend through the counties of Notting- 
 ham, Rutland, and Lincoln, and it probably reaches into 
 the Vale of York. 
 
 In these last counties, as well as in Staffordshire, Derby- 
 shire, Cheshire, and Lancashire, there is another very 
 different group of deposits. These consist of reddish or 
 chocolate-brown Boulder-clays, with interstratified beds of 
 sand, loam, and gravel, the latter containing in some 
 
263 NEOZOIC TIME. [CHAP. XIII. 
 
 places marine shells of species which now live on neigh- 
 bouring shores. These deposits occupy areas from which 
 the older clay appears to have been removed, and no clear 
 section has yet been found where the one clay overlies the 
 other, but there are several localities where the relative 
 ages of the two clays can be inferred from their relative 
 positions, and in every case the evidence points to the con- 
 . elusion that the chalky clay is older than the red and 
 brown clays. 1 
 
 The most recent and most detailed observations on the 
 later Glacial series of Yorkshire, 2 Lincolnshire, 3 Cheshire, 4 
 and Lancashire, 5 have shown that the supposed division of 
 these beds into an upper and lower Boulder-clay, separated 
 by a set of marine sands and gravels, is incorrect, the sands 
 and gravels being only lenticular beds and occurring at 
 various horizons in the series. 
 
 The southern limit of these newer clays in the Midland 
 counties has not yet been definitely ascertained, but pro- 
 bably they do not extend far to the south of the valley of 
 the Trent and its tributaries. It is worthy of mention also 
 that clay which closely resembles the red (Hessle) clay of 
 Lincolnshire occurs in the north of Norfolk, and occupies 
 a narrow strip of low ground between Hunstanton and 
 Wells. 
 
 Plateaux Gravels and Raised Beaches. South of the area 
 covered by the later Boulder-clays the latest G-lacial deposit 
 is a coarse gravel, consisting chiefly of quartzite pebbles 
 from the Trias and of flints from the Chalk, a deposit which 
 has the appearance of having been formed, partly from the 
 
 1 See " Quart. Journ. Geol. Soc.," vol. xli. p. 114 et seq. 
 
 2 " Geology of Holderness," C. Reid, " Mem. Geol. Surv.," 1886. 
 
 3 " Geology of East Lincolnshire," 1887, p. 76, and " Quart. Journ. 
 Geol. Soc.," vol. xli. p. 114. 
 
 4 A. Straban, " Quart. Journ. Geol. Soc.," vol. xlii. p. 369. 
 
 5 Mellard Keade, " Quart. Journ. Geol. Soc.," vol. xxxix. p. 83. 
 
Fig. 8. Map of the Cotteswold Hills (by Professor Hull). 
 
 The unshaded parts are the areas which are not covered by Drift. 
 figures indicate heights in feet. Scale about 7 miles to an inch 
 
 
270 NEOZOIC TIMS. [CHAP. xui. 
 
 destruction of the older Boulder-clay, and partly from the 
 disintegration of the Chalk, only the hardest stones having 
 survived the violent processes of erosion and transport. 
 These "plateaux gravels" occupy such positions as lead 
 to the inference that they once formed a nearly con- 
 tinuous sheet over the southern Midlands. South-westward 
 they occur on the higher parts of the low ground between 
 the Chalk escarpment and the Cotteswold Hills, but are not 
 found far above a level of 600 feet, the higher parts of 
 both ranges being entirely free from this northern Drift. 
 The limits of this Drift in the Cotteswold district were 
 first described by Professor Hull, 1 and represented on a 
 map which is reproduced in fig. 8 by permission of its 
 author and the Council of the G-eological Society. It has 
 been suggested that the area covered by these gravels was 
 a land surface at the close of the Glacial epoch, and that 
 the deposit was spread over its surface by the floods and 
 torrents resulting from the melting of the masses of snow 
 "which had accumulated on this part of the land. 
 
 In Hampshire there are gravels which occupy similar posi- 
 tions, the portions preserved showing that they originally 
 covered a wide plain or table-land which had a gentle 
 slope to the southward. The higher patches of these 
 gravels rise to a level of over 400 feet, and their lower 
 portions appear to be connected with certain marine 
 deposits or raised beaches which occur between the 
 heights of 20 and 100 feet above the present sea level. 2 
 Mr. Codrington infers that the lower gravels were deposited 
 in a shallow inlet of the sea during a period of upheaval, 
 by which the inlet was gradually narrowed into an estuary 
 ^which received the waters of rivers draining country to the 
 north, east, and south, the Isle of Wight being then con- 
 
 1 " Quart. Journ. Geol. Soc.," vol. xi. p. 477. 
 
 2 Codrington in " Quart. Journ. Geol. Soc.," vol. xxvi. p. 5C8. 
 

 CHAP. XIII.] PLEISTOCENE EPOCH. 271 
 
 nected with the mainland of Dorsetshire and having a 
 much further extension to the southward. 
 
 All the raised beaches of the southern and south-western 
 coasts of England appear to belong to an early Pleistocene 
 period, though it is remarkable that the shells they contain 
 do not indicate a low temperature, but, on the contrary, 
 one rather higher than now prevails on the coast. Thus 
 .among the shells of the Selsea deposits, several belong to 
 species which are now confined to the Mediterranean. In 
 Cornwall and Devon the height of the raised beaches is much 
 less than those of Dorset, Hants, and Sussex, but Mr. Ussher 
 has given good reasons for considering them to be older than 
 the stony loam (" Head ") and the submerged forests. 1 
 
 Fluviatile and Terrestrial Deposits. All the Glacial de- 
 posits, including the " plateaux gravels " last described, are 
 now trenched by valleys, in which are found river-formed 
 .gravels of various ages and at various heights above the 
 level of the modern stream. 
 
 Some of the oldest of these gravels contain two molluscs 
 which are now extinct in England, namely, Cyrena flumi- 
 .nalis and Unio littoralis, together with bones of Elephas 
 >antiquus, Rhinoceros tichorhinus, Rh. leptorhinus, and other 
 extinct mammalia, and the stone implements of Palaeo- 
 lithic man. Such gravels are, however, confined to the 
 southern and south-eastern counties, outside the limits of 
 the area in which the later Boulder-clays occur. 
 
 The Palaeolithic river-gravels are, therefore, only post- 
 glacial in the sense that they are later than the Glacial 
 deposits of the counties in which they occur, 2 but these 
 
 1 " The Post- Tertiary Geology of Cornwall," 1879, p. 43. 
 
 2 The Glacial age of the brick-earths near Brandon, which contain 
 'flint implements, has not yet been proved, for detailed evidence has never 
 ibeen published ; the statement rests on the simple assertion of Mr. 
 Skertchly, and is not universally accepted, in spite of its adoption by 
 Professor James Geikie in " Prehistoric Europe," p. 263. 
 
272 NEOZOIC TIME. [CHAP. XIII. 
 
 belong to the older Glacial series, and when we reach the 
 districts which are occupied by the newer Boulder-clays, 
 river-gravels are not so extensively developed, and appear 
 to be comparable only with the later river-deposits of 
 southern England, for they do not contain Palaeolithic im- 
 plements or the fauna of the older southern gravels. 
 Moreover, Cyrena fluminalis and remains of some of the 
 older mammals have been found in Lincolnshire and York- 
 shire beneath the highest sheet of Boulder-clay a fact 
 which raises the presumption that some of the so-called 
 Post-glacial gravels may have been contemporaneous with 
 the latest Glacial deposits on either side the Pennine 
 Hills. 1 
 
 The same assemblage of animals which occurs in the 
 older river-gravels is also found in the lower layers of the 
 cave-earths throughout the country, and it has been sur- 
 mised that many of these caves date from a period ante- 
 rior to the later Glacial deposits of northern England. In 
 the case of certain caves in the valley of the Clwyd in 
 North Wales, it is asserted that these deposits are banked 
 against the entrance of the cave in which mammalian 
 bones and flint implements have been found ; but the 
 exact relation of the inside and outside deposits is still a. 
 matter of doubt. 
 
 The old river-gravels are found in patches and terraces 
 which are as much as 80 or 100 feet above the level of the 
 nearest stream, and it is difficult to understand how the 
 rivers can have deepened their valleys to such an extent 
 since the formation of the gravels unless the land stood 
 for a long time at a much higher level than it does now. 
 This conclusion is confirmed by the depth of the valley- 
 beds below the sea-level near the coast, in some cases 
 amounting to 70 or 80 feet, for it is obvious that the stream 
 
 1 This was first suggested by Professor J. Geikie, see ' The Great 
 Ice Age," second edition, p. 526. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 273 
 
 could not excavate its channel below the level of low-water 
 mark. 
 
 The submerged forests which occur at so many points 
 round our coasts point to the same conclusion. A terres- 
 trial surface with rooted trees was found in Portsmouth 
 29 feet below high-water mark, and overlain by clay with 
 marine shells. In Cornwall a similar bed occurred at 67 
 feet below high- water mark ; but at varying levels above 
 this are other peat and forest beds indicating progressive 
 subsidence, and in southern England there is no evidence 
 of any subsequent elevation. 
 
 Ireland. 
 
 Glacial Deposits. These resemble the Glacial deposits of 
 Wales and western England, and there are probably two 
 groups or series of Boulder-clays, though these have not 
 yet been completely differentiated. In the mountain dis- 
 tricts there are tough Boulder-clays like those of northern 
 England and Scotland, and over the central plain there is 
 a wide spread of stony clays and gravels which consist 
 largely of the debris of the Carboniferous limestone. 
 Where this Limestone Drift reaches to mountain dis- 
 tricts it seems to have completely filled up the pre- 
 glacial valleys, and the aspect now presented by such 
 valleys is thus described by Professor Jukes : " The 
 steeper hills, as they descend into the valleys, are met by 
 gently sloping plateaus of Drift, forming inclined planes 
 from the heads of the valleys towards their mouths ; these 
 inclined planes seeming once to have stretched continu- 
 ously across the valleys, but being now deeply trenched 
 by the ravines at the bottom of which the present brooks 
 run. These have excavated channels for themselves either 
 through the Drift, or between it and the solid rock, leaving 
 the gently sloping surface of the Drift often most dis- 
 
274 NEOZOIC TIME. [CHAP. XIII. 
 
 tinctly marked along the flanks of the more abruptly rising 
 hills on each side of the valleys." ] 
 
 This Limestone Drift seems to be connected with a period 
 of submergence, for it sweeps up to heights of 1,200 and 
 1,300 feet, and at these heights there are marine deposits 
 like those of Wales, containing shells which do not indicate 
 any great intensity of cold, but include some species which 
 have a southern range, such as Venus casina and V. striatula. 
 
 In the north-east of Ireland and along the borders of 
 the Irish Sea deposits occur which are in part similar to 
 the low-level marine Drifts of western England, but the 
 notion that these and the older Boulder-clay on which they 
 rest constitute three distinct stages, namely, a set of sands 
 and gravels between two sheets of Boulder-clay, appears to 
 have been founded on a double misconception. In the 
 first place, such a general threefold division does not exist 
 in Lancashire (see p. 268) ; in the second, and assuming 
 that it does so appear in Ireland, it does not follow that 
 the lowest clay there is the same as the lowest Boulder- 
 clay in Lancashire ; that it is, in fact, a very different clay 
 we have the following testimony by Mr. Mellard Reade : 2 
 " What Hull calls the Lower Boulder-clay in Ireland is a 
 deposit of an entirely different nature to that of Lancashire, 
 which is undoubtedly marine, containing rounded boulders 
 of travelled stones as well as shell fragments. Whereas 
 the Irish Lower Boulder-clay is distinguished by the local 
 character of the stones it contains, the absence of shells or 
 shell-fragments, and the general appearance (? resemblance) 
 it bears to moraine matter." 
 
 Neither do the facts recorded by Messrs. Hull, J. G-eikie, 
 and Hardman, 3 afford sufficient ground for labelling any 
 
 1 <: Manual of Geology," second edition, p. 676. 
 
 2 " Notes on the Geology of Ireland,'' Proc. Liverp. Geol. Soc.. 1879. 
 
 3 See " The Great Ice Age," second edition, p. 595, for details and 
 references. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 275 
 
 group of mariiie sands and gravels either in Ireland or 
 England as " Interglacial," that is to say, they are not 
 justified in regarding such beds as belonging to a phase of 
 Pleistocene time which was distinct and separate from the 
 epochs when Boulder-clay was formed. In Ireland, as in 
 England, there appear to be two groups of Glacial deposits, 
 an older and a newer, each including Boulder-clays and 
 gravels ; and the sands and gravels which occur at low 
 levels on the eastern coast and contain marine shells are 
 closely connected with the sandy Boulder-clay which over- 
 lies them. 
 
 Non-Glacial Deposits. Baised beaches occur at many 
 places, especially round the northern half of Ireland, but 
 there is much difference of opinion regarding their number 
 and relative levels. Mr. Kinahan describes two distinct 
 and well-marked beaches, 1 a lower at or below 12 feet from 
 high- water mark, and a higher between 20 and 25 feet ; 
 but Professor Hull states 2 that the level of the 20-foot 
 terrace declines southward, so that between the mouth of 
 the Boyne and the north shores of Dublin Bay it varies 
 from 8 to 3 or 4 feet, and along the south shores the ter- 
 race cannot be identified, as it merges into the present 
 strand. Possibly this local declination is due to a change 
 in the position of the "head of the tide," as Mr. Kinahan 
 suggests, and the Dublin beach may belong rather to the 
 12-foot terrace. 
 
 No ancient river-gravels containing Palaeolithic imple- 
 ments have yet been found in Ireland, the Welsh hills and 
 glaciers having apparently formed a barrier to the migra- 
 tion of man at that time. The mammoth and many of its 
 congeners have, however, left their remains in some of the 
 caves of southern Ireland, and the inland lakes and bogs 
 
 1 " Geology of Ireland," p. 252 et seq. 
 
 3 " Expl. of Sheets 102 and 112 of Geol. Survey of Ireland/' 1875, 
 p. 69. 
 
276 NEOZOIC TIME. [CHAP. XIII. 
 
 have yielded numerous remains of the reindeer, Irish 
 elk, &c. 
 
 Submerged forests are of frequent occurrence round the 
 western, southern, and eastern coasts ; they pass below low- 
 water mark, and peat is said to have been found in some 
 places below four or five fathoms of water. In the estuary of 
 the Barrow the depth of alluvial matter extends to between 
 60 and 70 feet below high- water mark. 1 
 
 2. Physical History and Geographical Changes. 
 
 Amid the conflicting opinions which are held by different 
 geologists regarding the physical conditions that prevailed 
 during the early part of the Pleistocene period, it is very 
 difficult to come to any decided conclusion. Everyone 
 admits that it was a time when the action of ice was para- 
 mount, but what form of ice chiefly prevailed over the 
 British Islands at the climax of this ice age, and whether 
 at this particular epoch the land surface stood at a higher 
 level than now, or was submerged beneath the waters of an 
 ice-laden sea, are matters of dispute. 
 
 That this should be the case with a period of such a late 
 geological date, of which we have such complete records, 
 and of which so many competent observers have made a 
 study, might be deemed a remarkable fact, and one that 
 did not redound to the credit of geologists generally ; but 
 the prevailing uncertainty is, without doubt, caused by the 
 difficulty of realizing the exceptional conditions which must 
 have existed in the British area at this time. The ice- 
 regions of the present day are difficult of access, and we 
 cannot study the action of ice-masses with the same facility 
 that we can observe the action of rivers or of sea- waves. 
 Here and there we may find a retreating glacier, and can 
 
 1 Kinahan, '' Geology of Ireland," pp. 265 and 266. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 277 
 
 examine the work it has done and the deposits it has left 
 behind, but a country from which an ice-sheet has recently 
 retreated has yet to be found and described. It is quite 
 conceivable that the action of an extensive ice-sheet may be 
 different from that of a single glacier ; while the action of 
 sea-ice on a sinking shore is likely to be very different from 
 both. 
 
 As however very little is known about these agencies, 
 the students of Glacial deposits labour under the disad- 
 vantage of being without positive knowledge of what takes 
 place at the present day under the conditions which they 
 postulate as having existed at a past period in Britain. 
 They are obliged to draw largely on the imagination, and 
 there has been a great tendency to refer all the phenomena 
 of the Glacial epoch to one set of conditions or the other 
 without duly considering the differences of the deposits. 
 Probably in this, as in so many other much debated ques- 
 tions, the truth lies between the opposite extremes, and the 
 investigator who is most likely to arrive at the truth is he 
 who takes care to steer a safe course between the Scylla 
 of universal land-ice on the one hand, and the Charybdis 
 of floating icebergs on the other. 
 
 In the following pages I shall not attempt to give a 
 complete history of the physical and geographical changes 
 which took place in the British area, but shall content 
 myself with giving some reasons for not accepting the 
 accounts which have been given by Professor James Geikie, 1 
 and shall then fix the reader's attention on certain epochs 
 concerning which there is a more general agreement of 
 opinion. 
 
 In the first place, Professor James Geikie probably errs 
 in attributing all ice-scratched surfaces to the action of 
 land-ice, and in not admitting that some of them may be 
 
 1 In " The Great Ice Age " and " Prehistoric Europe." 
 
278 NEOZOIC TIME. [CHAP. XIII. 
 
 due to the action of floe-ice carried in a definite direction 
 by a steady current. In the next place, he assumes that 
 all Boulder-clays are the " ground-moraines " of confluent 
 glaciers or ice-sheets, and that they have invariably been 
 formed between such ice- sheets and the land surfaces over 
 which the ice passed. That such confluent glaciers existed 
 during the Ice Age in Britain I would not deny, but it by 
 no means follows that the various Boulder-clays were each 
 and all formed on the surface of the land. There is great 
 difficulty in understanding how a country could be glaciated 
 and at the same time covered with an almost universal 
 mantle of Boulder-clay if both processes were effected by 
 an ice- sheet moving over dry land. For if the thickness 
 and weight of the ice were such that its base conformed 
 to the surface of the country, and the pressure it exercised 
 so great that every slight prominence was scratched, 
 grooved and moulded by the stones frozen into the ice, how 
 could there be room at the same time for a layer or pad of 
 compacted mud to accumulate between the ice and the 
 rock? Professor Geikie has been confronted with this 
 difficulty, and he admits that it is impossible for the two 
 operations to take place at the same place and at the same 
 time, but he suggests that the clay was formed under 
 those parts of the ice where the pressure was least, and 
 that the rock was only scratched where the pressure was 
 greatest. If Boulder-clay was found to fill lake-like 
 hollows this explanation might be accepted, but since it 
 behaves as if it had originally formed an almost universal 
 mantle over all the lower parts of the country, the suppo- 
 sition cannot be admitted. Moreover, Professor G-eikie 
 often disregards his own suggestion and refers the for- 
 mation of a Boulder-clay overlying a glaciated surface to 
 the action of the ice which scratched that surface. To 
 most minds I think the obvious inference would be that 
 the scratching must have been done first, and that the clay 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 279 
 
 was subsequently laid down upon it ; and further, that the 
 conditions which permitted the clay to accumulate were 
 different from those which allowed the rock to be scratched. 
 
 Finally, those who hold the land-ice theory are com- 
 pelled to admit not one Glacial period only, nor even two, 
 but an indefinite number of such periods, separated by an 
 equal number of non- glacial and comparatively warm 
 periods, solely because beds of stratified sand and gravel 
 containing marine shells are frequently found between 
 sheets of Boulder-clay. Every such bed is for them a 
 record of an " Inter glacial period," and each sheet of 
 Boulder-clay is the record of a distinct Glacial period sepa- 
 rated from that of the clay below by an enormous interval 
 of time ! To anyone who is familiar with the Glacial 
 series of England, where such intercalations of sand, 
 gravel, and loam are frequent, such a view must seem a 
 very forced and unnatural method of explanation. 
 
 Professor J. Geikie's presentation of the ice-sheet theory 
 is,^ however, by no means the only way in which this 
 theory ca.n be applied, and it is quite conceivable that a 
 modification of it is capable of explaining the Glacial phe- 
 nomena of Scotland. We may grant that the moulding 
 and grooving of the rock surface has been accomplished by 
 an ice-sheet composed of confluent Scottish glaciers, and 
 indeed few could read Dr. Archibald Geikie's admirable 
 descriptions of Scottish scenery 1 without admitting the 
 former presence of such an agent ; but we must urge that 
 some change took place before this surface could have been 
 so largely covered with Boulder-clay. A possible supposi- 
 tion is that the ice-sheet remained, but that a general subsi- 
 dence of the whole country occurred ; the detritus which 
 was being scoured off the face of the land would then come 
 to rest where the pressure of the ice-sheet was relieved by 
 
 1 " The Scenery of Scotland/' second edition, 1887. 
 
280 NEOZOIC TIME. [CHAP. XIII. 
 
 the letting in of sea-water beneath it, and this would take 
 place at a considerable depth below the surface of the sea, 
 all wave-action being completely prevented by the mass of 
 ice above. The inland extension of the Boulder-clay which 
 was thus allowed to form beneath the ice and the land 
 would only be limited by the progress of the submergence 
 and the variations in the thickness of the ice. Dr. J. Young, 
 the Eev. Boog Watson, and others have felt the same diffi- 
 culty in understanding the formation of Boulder-clay 
 underneath land-ice, and have suggested an explanation 
 which is substantially the same as that above offered. 1 
 
 If, for instance, this subsidence took place before the 
 climax of the Glacial period, and the ice continued to in- 
 crease in thickness, a pause in the downward movement 
 would enable it to exercise pressure and erosion on the 
 material which had accumulated beneath it. Nay, it is 
 conceivable that the partial flotation of the Scandinavian 
 ice- sheet might enable this to cross the great plain of the 
 North Sea and to impinge upon the edge of the Scottish 
 ice- sheet, as Dr. Croll has suggested that it did (without 
 any such assistance). The increased pressure so caused, 
 and the different direction given to the movement of the 
 ice-masses, would then explain the existence of two distinct 
 lines of glaciation in Aberdeenshire, a point to which Pro- 
 fessor J. Geikie gives far too little attention. Probably all 
 the phenomena of the Glacial deposits of Scotland could be 
 explained more satisfactorily on the hypothesis of one sub- 
 sidence, and a subsequent upheaval during the prevalence 
 of glacial conditions, than on that proposed by the author 
 of " The Great Ice Age," for he admits a submergence in 
 late Glacial times which depressed the country at least 500 
 feet, and probably from the evidence in England and 
 Wales to a much greater extent. 
 
 1 "Geol. Mag.," 1878, p. 162, and "Trans. Roy. Sue. Edln.," vol. 
 .xxiii. p. 539. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 281 
 
 I do not propose, however, to venture on any detailed 
 application of the hypothesis, but only to note that when 
 the land had risen again to within 100 feet of its present 
 level in Scotland, there seems to have been a pause, during 
 which the latest marine beds containing Arctic shells were 
 formed, while glaciers still occupied the Highland valleys. 
 Lastly, it may be observed that the action of these last 
 glaciers has hardly been sufficiently studied. Mr. Jamieson 
 has discussed some of their effects l in the way of sweeping 
 out the traces of the marine occupation of the country ; 
 but it is not unlikely that the present patchy distribution 
 of Boulder-clay in the higher parts of certain valleys is due 
 to their action, the clay being left where these compara- 
 tively feeble glaciers had not sufficient power to remove it. 
 Again, the arrangement of Boulder-clay into " drums," 
 " sow-backs," and similar ridges is more likely to be the 
 work of retreating than of advancing ice. 
 
 Mr. J. Gr. Goodchild has suggested another explanation 
 of the formation of Boulder- clay, which has much to 
 recommend it. 2 He has evidently felt the difficulty of 
 conceiving the possibility of material accumulating under 
 an advancing ice- sheet, and sees that Professor J. Greikie's 
 theory is incapable of explaining either the internal struc- 
 ture or the external configuration of Drift mounds. He 
 relies on the fact that both glacier-ice and polar-ice are 
 always more or less dirty, and on J. D. Forbes' observa- 
 tion that the lower layers of glacier-ice work up toward 
 the surface as the whole moves onward. He naturally 
 infers that the rock detritus does not remain at the 
 bottom of the moving ice, but that the whole mass becomes 
 charged with the products of erosion, both in the form of 
 mud and of stones and boulders. So long as the ice is in- 
 
 1 " Quart. Journ. Geol. Soc./' vol. xxx. p. 320. 
 
 2 Ibid. vol. xxxi. p. 55 ; " Geol. Mag.," Dec. 2, vol. i. p. 496, and 
 " Trans. Cumb. and West. Assoc.," 1887, No. xi. p. 111. 
 
282 NEOZOIC TIME. [CHAP. XIII. 
 
 creasing and advancing he does not think any Boulder- 
 clay would be formed, but when it ceased to move and 
 began to melt, the load which it carried would be gradually 
 deposited, and most of it would eventually settle down on 
 the surface over which the ice came to rest. Melting would 
 go on over both the lower and the upper surfaces of the 
 ice, which, though ceasing to glaciate, would still exercise 
 great vertical pressure, compacting the material thawed 
 out of its lower layers into Boulder-clay, except here and 
 there where this might undergo a rearrangement by sub- 
 glacial streams. 
 
 Mr. G-oodchild only applies this hypothesis to the Drifts 
 of mountain districts, and does not seem to have considered 
 what might take place in those areas where the ice had 
 usurped the place of the sea. Indeed, he is needlessly 
 sceptical about the submergence which even the most ex- 
 treme glacialists are prepared to admit ; but it would 
 probably repay anyone who was studying an area where 
 marine Drifts abutted against a mountain district to con- 
 sider whether some modification of Mr. Goodchild's hypo- 
 thesis would not explain the intercalation of marine sands 
 and shelly Boulder-clays. 
 
 With regard to the Glacial deposits of England and Ire- 
 land, the hypothesis which assumes that the Boulder-clays 
 were laid down on an actual land surface is still more inap- 
 plicable than in the case of Scotland. The proofs of the 
 presence of sea-water are much more apparent and uni- 
 versal ; the Glacial deposits extend over much broader 
 areas of comparatively low ground, and though a certain 
 kind of succession can be made out in some localities, there 
 is nothing like the definite arrangement of Boulder- 
 clays which Professor J. Geikie has assumed, and which 
 three or four distinct ice- sheets ought certainly to have 
 produced. 
 
 To commence with the oldest or Cromer Drifts, the 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 283 
 
 following are points which call for explanation : (1) that 
 the lowest Boulder-clays are not persistent sheets, but are 
 lenticular beds seldom more than ten feet thick, and sepa- 
 rated by laminated and ripple-marked sands and clays, and 
 these beds are broken off and worked up into contor- 
 tions of the overlying beds to the northward of Trimming- 
 ham ; (2) that the Contorted Drift contains the spoils of a 
 sea-bottom, together with boulders which probably came 
 from Scandinavia, while the upper Chalky clay does not ; 
 (3) that the inland sands and gravels often include 
 irregular and contorted masses of Boulder-clay similar to 
 the Chalky clay which overlies them, and also contain 
 broken marine shells ; (4) that the upper Boulder-clay con- 
 tains Lower Cretaceous and Jurassic detritus, the quantity 
 of which increases north-westward, a fact which proves 
 the ice which formed it to have come chiefly from that 
 direction. 
 
 Passing to the later Glacial deposits described on pp. 
 267 and 268, it may be remarked that the abolition of the 
 old classification of these beds deprives the author of " Pre- 
 historic Europe " of the basis on which he constructed his 
 account of the conditions which prevailed during the forma- 
 tion of the Purple and Hessle Clays (op. cit., pp.266, 267), 
 and adds force to the objections which have already been 
 urged against his theory of the formation of Boulder- 
 clays. 
 
 The presence of the sea during the period of their forma- 
 tion is still more marked than in the case of the East 
 Anglian Drifts, and the materials of which they consist 
 have all been transported from a greater or less distance, 
 so that they contrast strongly in this respect with the older 
 Chalky Boulder-clay, but whether they were accumulated 
 during the uprise of the land from a previous great sub- 
 mergence, or whether a fresh land surface was first formed 
 and a second submergence took place, cannot yet be deter- 
 
84 NEOZOIC TIME. [CHAP. XIII. 
 
 mined, though I have elsewhere recorded facts which seem 
 to favour the latter supposition. 1 
 
 I would here remark that though Professor J. Geikie 
 admits the occurrence of a great submergence by which 
 England, Wales, and Ireland were depressed to at least 
 1,500, and probably to 2,000 feet below the sea-level, yet 
 the deposits which he would refer to the epoch of this 
 grand subsidence are few and physically unimportant. He 
 excludes every Boulder-clay from the category of marine 
 deposits, and explains the absence of thicker and more 
 extensive records of this important episode by the hypo- 
 thesis that they were swept out and worked up into the 
 Boulder- clays formed by a second great ice -sheet after the 
 country emerged from the sea. He is therefore under the 
 necessity of supposing that the second ice-sheet was nearly 
 as extensive and as massive as the first, a result which he 
 himself appears to consider surprising, as it certainly is. 
 If, however, we admit that the later Boulder-clays were 
 formed during the submergence and on the sea-floor, no 
 such necessity arises, and we possess in them, and the 
 shelly sands associated with them, a set of deposits which 
 is more proportionate to the magnitude of the subsidence 
 and the time it must have occupied. 
 
 It is remarkable that no Drift with marine shells has 
 been found at similar high levels in Scotland, a fact which 
 seems explicable only on the supposition that the conditions 
 in England and Scotland were essentially different, and 
 that the mass of ice which had previously accumulated 
 over Scotland was so thick as to keep out the sea-water 
 and to prevent its ever rising much above the contour of 
 600 feet. Professor G-eikie himself estimates the thickness 
 of the Scotch ice at more than 2,000 feet, and observes that 
 " to cause such a mass to float, the sea around Scotland 
 
 1 "Quart. Journ. Geol. Soc.," vol. xli. p. 128, and "Geol. Mag.," 
 1887, p. 147. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 285 
 
 would require to become deeper than now by 1,400 or 1,500 
 feet at the least." l Now if we add the latter depth to the 
 height at which marine shells occur at Chapelhall (526 
 feet) we obtain a total of over 2,000 feet, which is just 
 the extreme amount of subsidence indicated by the Welsh 
 Drifts. 
 
 This consideration appears also capable of explaining 
 what Professor J. Geikie calls an "insuperable objection '* 
 to Mr. Mackintosh's views regarding the dispersal of 
 erratics over England. Many of these erratics have come 
 from Criffel in Galloway, and Professor Geikie thinks it 
 " very strange that there is not a vestige or trace of any 
 such submergence either in the neighbourhood of Criffel 
 itself or in the region to the north of it ; " 2 but if the ice 
 had anything like the thickness he supposes, it is clear that 
 it would never loose hold of Criffel during the subsidence 
 unless it was melted off by a rise of temperature, and the 
 absence of marine shells consequently ceases to be smv 
 prising, if indeed it ever was very much to be won- 
 dered at. 
 
 Admitting, however, that in the present state of know- 
 ledge and opinion it is unsafe to attempt any connected 
 account of the physical history of the Great Ice Age in 
 Britain, there are, nevertheless, certain well-ascertained 
 facts upon the interpretation of which nearly everyone is 
 agreed, and these enable us to indicate with tolerable cer^ 
 tainty some of the geographical changes which took place 
 during the prevalence of Glacial conditions ; changes which 
 were largely concerned in the development of the present, 
 geographical outlines and physical features of the British 
 Islands. 
 
 It was stated on p. 246 that the slight submergence with 
 
 1 " The Great Ice Age," second edition, p. 186. 
 
 2 " The Intercrossing of Erratics in Glacial Deposits " (" Scottish, 
 Naturalist," 1882). 
 
286 NEOZOIC TIME. [CHAP. XIII. 
 
 which the Pliocene period seems to have closed was not of 
 long duration, and that it was succeeded by a movement 
 of upward tendency. One proof of this is the occurrence 
 of a peculiar bed containing Arctic plants and animals 
 and small land-shells between theLeda myalisbed. and the 
 lowest Boulder-clay of the Norfolk coast. The fauna and 
 flora of this bed (so far as at present known) are so very 
 different from those of the Forest Bed below, 1 and so much 
 more Arctic in character, that the change in the climatal 
 conditions must have been very great, and could hardly 
 have taken place in a short space of time ; it would appear, 
 therefore, that the period of time which elapsed between 
 the formation of the Forest Bed and this Arctic plant 
 Bed was a long one, and that in the course of this unrepre- 
 sented time the whole of East Anglia, and probably the 
 whole of Britain, was raised far above the level of the sea. 
 This important conclusion, however, does not rest entirely 
 upon the evidence of the Arctic plant Bed, it is supported 
 by other facts, and especially by a consideration of the 
 tmried river- valleys which occur round our northern coasts 
 and the depth to which they were evidently excavated 
 during the interval between the formation of the Pliocene 
 and Pleistocene deposits of Norfolk. The position of the 
 latest Pliocene beds proves that the country at the close 
 of that period was at a rather lower level than it is now, 
 while the depth to which the valleys were cut before they 
 were filled with Boulder-clay proves that the land had at 
 some intervening time stood at a much higher level than 
 it does now. Thus the bottom of the valley formed by 
 the rivers which flowed through the gap in the Chalk 
 escarpment now filled by the Wash (see p. 256) is at 
 Boston 180 feet below the sea-level ; the pre-glacial channel 
 of the Tees is 200 feet below the sea, and that of an old 
 
 1 See " Geology of Cromer," Mem. Geol. Survey, by C. Heid, p. 83. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 287 
 
 valley opening into the Firth of Forth at Grangemouth is 
 260 feet below the same level. 
 
 It is clear, therefore, that the difference between the 
 level of the late Pliocene and early Pleistocene land surfaces 
 amounted to several hundred feet. This upheaval was 
 doubtless sufficient to restore the land connection between 
 Scotland and Greenland which had been temporarily inter- 
 rupted during Pliocene times, and the influence of this 
 geographical change in accelerating the rate at which snow 
 and ice were accumulating in our latitudes must have been 
 very great. Changes in the direction of the Arctic currents, 
 and possibly also a deflection of the Gulf Stream (see 
 "Historical Geology," p. 562) were likewise important 
 factors in producing that intensity of Arctic cold and that 
 southerly extension of the Arctic climate which is known 
 as the Glacial Period. For if at the present time Britain 
 were united to Greenland and the Gulf Stream deflected 
 from our shores, so that both our eastern and western 
 coasts were washed by currents from the Arctic regions, it 
 is certain that the climate would return to something very 
 like the conditions of the Glacial Period. 
 
 It was probably during this elevation of the British 
 area that the early glaciation of Scotland and northern 
 England was accomplished, and it can hardly be doubted 
 that the agents concerned in this glaciation were confluent 
 glaciers or ice-sheets. The relation of the Boulder-clays to 
 this glaciation is a matter which has already been partially 
 discussed, and as I wish to avoid asserting that all Boulder- 
 clays were formed in the same manner, I will ask the 
 reader to consider that the application of the following 
 remarks is confined to the Glacial deposits of the English 
 lowlands and the borders of the Irish Channel, and more 
 especially to the later portions of these deposits. 
 
 The change which led to the formation of these deposits 
 appears to have been a general subsidence by which the 
 
288 NEOZOIC TIM3. [CHAP. XIII. 
 
 outer parts of the great ice-slieets which had accumulated 
 over Scandinavia, Scotland, the Lake District, Wales, and 
 parts of Ireland, were brought within the reach of the 
 waves. As successive tracts of land and ice were carried 
 beneath the level of the sea, the ice would be broken up 
 into large noes and bergs, which, mingled with others 
 brought from the Arctic regions by the northern currents, 
 would form powerful agents of corrasion, propulsion, and 
 compression of material on any shores against which they 
 might be driven. 
 
 During this phase of the period the material which had 
 previously been swept by glaciers out of the mountain 
 valleys on to lower ground would come under the action of 
 coast-ice and marine currents ; by these agencies it would 
 be re-arranged, much of it kneaded up into Boulder-clay 
 and spread out as wide sheets of that material, while other 
 portions were sorted into beds of loam, sand, and gravel. 
 It was probably by the action of coast-ice on subsiding 
 tracts of land that stones and boulders derived from sites 
 at comparatively low levels were carried up to the positions 
 where they are now found. 
 
 It was at this time, too, and by the ordinary action of 
 waves on an exposed coast-line, that so much of Yorkshire 
 and Lincolnshire was destroyed, that the bay of the Wash 
 was formed, and a line of cliffs carved out of the eastern 
 side of the Chalk Wolds of Lincolnshire ; cliffs that were 
 afterwards battered into slopes by the impact of ice-floes, 
 and finally buried under the accumulation of Boulder-clay 
 which now conceals them. 
 
 The opponents of the formation of Boulder- clays by 
 marine ice have often asked the upholders of that view to 
 point to the occurrence of deposits containing perfect and 
 undisturbed marine shells in association with Boulder-clay. 
 It is of course very seldom that such deposits would be 
 preserved, but the fossiliferous loams of North Lincolnshire 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 289 
 
 are, I believe, calculated to satisfy these requirements. 
 As the land sank lower and lower, such deposits were 
 carried farther and farther over its surface, and their accu- 
 mulation only ceased when Britain was reduced to a group 
 of islands, the high-level shelly gravels being probably 
 nearly the last deposits formed during the great subsidence, 
 and possibly these were formed after it had reached its 
 maximum extent. 
 
 Mr. Mackintosh thinks that the water-worn character of 
 the pebbles in the high-level gravels of Wales, as con- 
 trasted with the angular character of the blocks at lower 
 levels, indicates a decrease in the rate of submergence, and 
 says, " at this period the district was probably in the 
 condition of a littoral zone, which may have lasted for a 
 time sufficient to enable the waves to round the stones, and 
 to allow the mollusca to multiply in the littoral and sub- 
 littoral zones." l The occurrence of such shelly gravels at 
 about the same level in Ireland, Wales, and at Maccles- 
 field Forest confirms this idea of Britain having remained 
 stationary for some time when the sea was at this level. 
 It must be remembered, too, that the submergence of the 
 land would partially ameliorate the severity of the climate 
 and enable some mollusca of less Arctic habit to live in the 
 sea which then covered our islands. 
 
 From the icy sea by which it was submerged Britain 
 gradually rose again, and as the mountains rose higher and 
 higher above the water they were again covered by ice and 
 snow, but these did not accumulate to anything like their 
 previous thickness, because the conditions which had caused 
 the Glacial episode in the northern hemisphere were now 
 passing away. Snowfields, however, formed on the hills 
 of Scotland, Ireland, Cumberland, and Wales, generating 
 local glaciers, which have left small moraines to mark the 
 
 1 <; Quart. Journ. Geol. Soc.," vol. xxxvii. p. 362. 
 U 
 
290 NEOZOIC TIME. [CHAP. XIII. 
 
 limits of their descent. The lower ground, when it rose 
 above the sea, appears to have been quite free from perma- 
 nent snow, and was tenanted by the numerous animals 
 which ha.ve left their bones in the caves and the river- 
 gravels. 
 
 The rainfall, however, was probably greater than it is 
 now, and the country being covered with an almost uni- 
 versal mantle of Boulder-clay, no large tracts of pervious 
 rock were then exposed, such as now absorb a portion of 
 the rainfall ; consequently, nearly all the rain was shed off 
 the land in the shape of running water, all the streams and 
 rivers were larger and swifter than they are at present, and 
 the process of valley erosion was thus carried on at a rapid 
 rate. 
 
 Since the Glacial deposits to a great extent draped the 
 pre-glacial surface of the country without completely filling 
 up the pre-existent valleys, the streams were naturally 
 directed into the same depressions ; but the channel which 
 each began to carve out of the G-lacial Beds did not every- 
 where coincide with that of the river which occupied the 
 valley in pre-glacial times, so that in many cases we have a 
 post-glacial valley system superimposed upon an antecedent 
 one, as in the case of the Mersey and of many rivers in 
 Scotland (" Physical Geology," p. 61). Cases also occur 
 where the older valleys have been so blocked up by Glacial 
 deposits at certain points that the post-glacial streams 
 were ponded back, and have made new channels for them- 
 selves through the country between the older valleys ; inte- 
 resting instances of this occur in Lincolnshire. 1 
 
 It is not certain, however, that there was only one epoch 
 of submergence during the continuance of glacial condi- 
 tions, and there are reasons for thinking that there were 
 two such epochs. Again, it is possible that the upheaval 
 
 1 See " Quart. Journ. Geol. Soc.," vol. xl. p. 160. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 291 
 
 which followed the deepest submergence was not of uniform 
 extent, and that southern England was raised above the 
 sea, while large parts of northern Britain were still below 
 it, and while Boulder-clays were still being accumulated 
 over them. Those who take this view would probably 
 regard the plateau gravels as deposits formed by snow-fed 
 torrents during this period of elevation. Certainly the 
 phenomena of the river-gravels of this part of England 
 are such as to make it probable that it has never been over- 
 whelmed either by water or ice since an early date in 
 Pleistocene time. 
 
 Without therefore attempting to fix the exact relative 
 dates of the surface deposits of northern and southern 
 England, the inferences to be deduced from a study of the 
 latter region may be put in the form of three propositions. 
 
 (1) That at some period after the greater submergence 
 southern England and Ireland were raised to a much higher 
 level than their present position above the sea, and Britain 
 was united to France. 
 
 (2) That this was followed by a gradual subsidence 
 which, assisted by the action of the sea, was eventually 
 sufficient to disunite England from Ireland and from the 
 Continent. 
 
 (3) That the present geography of Britain was produced 
 by a differential movement, England continuing to sink, 
 while Scotland was raised to its present level. 
 
 To the first of these conclusions, that England formed 
 part of the European continent and Ireland was united to 
 England, and probably also to Scotland, we are led by three 
 distinct lines of evidence, viz., (1) the existence of the 
 mammalian fauna which is known as that of the older 
 cave-earths and river-gravels (later Pleistocene of Professor 
 Dawkins) over the greater part of England and in the south 
 of Ireland ; (2) the position of the older river- gravels in the 
 valleys, and their abrupt termination near the mouths of 
 
292 NEOZOIC TIME. [CHAP. XIII. 
 
 the present rivers ; (3) the occurrence of mammalian 
 remains on the bed of the North Sea, and especially on the 
 Dogger Bank. 
 
 In the first place, it is certain that when Palaeolithic 
 man and the animals which are associated with his re- 
 mains invaded Britain, the rigour of the Ice Age must 
 have passed away, and the climate of the southern portion 
 of the country must have been mild enough for the growth 
 of an abundant vegetation ; the country must, in fact, have 
 been in a condition to support large herds of herbivorous 
 animals. 
 
 To enable terrestrial animals to cross freely from France 
 and Belgium to England, the elevation required would not 
 be more than 25 fathoms (150 feet) ; but the central part 
 of the Irish Sea and St. George's Channel is everywhere 
 more than 50 fathoms deep, except over a small area 
 opposite Cardigan Bay, where the deepest parts are between 
 40 and 50 fathoms. It would therefore require an eleva- 
 tion of at least 50 fathoms (about 300 feet) to unite Ireland 
 with Wales. Even then long and deep lakes would remain 
 in the bed of the Irish Sea, for there is a tract extending 
 from off the west coast of Carnarvon to the Sound of Jura, 
 where the soundings are continuously over 50 fathoms, 
 and generally over 60, so that if the elevation reached the 
 latter figure these lakes and their excurrent river would 
 form a definite line of separation between Great Britain 
 and Ireland. 1 
 
 It might be supposed that the formation of the Straits 
 of Dover and of St. George's Channel was effected by 
 marine erosion rather than by subsidence, and that the 
 present depth of these channels could not be taken as 
 affording any measure of the elevation of the land previous 
 to their formation ; so that in order to restore the condi- 
 
 1 J. Geikie in " The Great Ice Age," second edition, p. 294, and map. 
 See also " Prehistoric Europe," by the same author. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 293 
 
 tions of the time when the countries were united it would 
 only be necessary to imagine the replacement of material 
 cut away by the sea. But if the whole displacement were 
 due to marine erosion, we should expect the minimum 
 depth of the two channels to be approximately the same, 
 whereas the actual difference is very great, being no less 
 than 120 feet. Again, we know that subsidence has actu- 
 ally taken place, and it is more reasonable to suppose that 
 it was this movement which carried the sea over the greater 
 part of the submerged area, only the final breach being 
 directly accomplished by the waves. The vertical displace- 
 ment so effected would be small, and we may, I think, 
 fairly regard the present depth of the channels as indica- 
 ting the relative levels of the connecting isthmuses, unless 
 it can be shown that the submergence was not of uniform 
 extent. 
 
 To account, therefore, for the dispersion of these large 
 extinct quadrupeds we must suppose that at one time the 
 whole of Britain stood at least 300 feet higher than it 
 does now, so that they could make their way westwards 
 along the bed of the Bristol Channel to the south of 
 Ireland. 
 
 From the river- gravels we cannot learn much as to the 
 absolute elevation of the land, but their abrupt termina- 
 tions prove that the rivers had far longer courses than they 
 have now. Thus in the case of the Thames the height of 
 the old gravels above the present estuary (over 100 feet at 
 Dartford Heath), and the entire absence of estuarine shells 
 in them, prove that the course of the ancient river was 
 continued far beyond its present mouth. 
 
 The Dogger Bank affords more precise evidence. This 
 bank may be described as a submerged island in the middle 
 of the southern part of the North Sea ; its border is about 
 75 miles E.N.E. of Flamborough Head, and that part of 
 its surface which rises to within a depth of 10 fathoms is 
 
294 NEOZOIC TIME. [CHAP. XIII. 
 
 no less than 250 square nautical miles in extent ; a still 
 larger area is within the 15-fathoni line, while it is separated 
 from England by a channel which is from 27 to 40 fathoms 
 deep. 1 From this bank many hundred specimens of bones, 
 teeth, and antlers have been dredged up, belonging to the 
 mammoth, woolly rhinoceros, horse, bison, urus, reindeer, 
 Irish elk, stag, hyaena, bear, wolf, and beaver. 2 
 
 Professor Dawkins points out that they cannot have 
 been carried there by sea currents, and thinks that the car- 
 casses were " collected in the eddies of a river that helped 
 to form the Dogger Bank." It is difficult, however, to see 
 how a river could form so large a bank, though it may be 
 credited with having formed the adjoining channel or 
 valley. Mr. J. Murray was of opinion that the channel, 
 and the deep water generally round the bank, were due to 
 the circulation of the tidal currents, and that the bank 
 itself had resulted from the heaping up of materials in the 
 centre of the circulating water. The occurrence of so 
 many osseous remains on the bank is, however, against the 
 view that it has been heaped up in this manner, and it is 
 just as probable that the pre-existence of the bank and the 
 channels was the cause of the present circulation of the 
 water. 
 
 The bank is in fact a submerged plateau, which before 
 submergence appears to have supported large tracts of 
 sands and gravels deposited by the rivers which had coursed 
 over its surface, these tracts doubtless forming patches 
 and ridges similar in their mode of occurrence to those 
 that exist in the eastern counties at the present time. 3 
 The Dogger Bank is not the only spot in the bed of the 
 
 1 See J. Murray, " On the North Sea, Proc. Inst. Civ. Eng.," vol. 
 xx. p. 320. 
 
 2 Boyd Dawkins, " Early Man in Britain," p. 149. 
 
 3 Mr. H. B. Woodward takes the same view; see "Geology of 
 England and Wales," second edition, p. 516. 
 
PLATE XIV. GEOGRAPHY OF THE EPOCH IN PLEISTOCENE TIME, WHEN THE 
 COAST-LINE COINCIDED WITH THE CONTOUR OF 80 FATHOMS. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 295 
 
 North Sea where bones have been dredged, but Pleistocene 
 remains are not so abundant elsewhere. 
 
 An elevation of the bed and borders of the North Sea to 
 the extent of 40 fathoms (240 feet) would now convert the 
 Dogger Bank and all the surrounding parts of the sea-bed 
 into land. The Rhine would make its way through the 
 upraised country, and the rivers of eastern England would 
 at once become its tributaries. A subsequent submergence 
 of 20 fathoms would convert the Dogger into an island 
 round which the currents would circulate as they do now, 
 and it is probably to this isolation of the plateau that the 
 preservation of the ossiferous gravels is due ; sandbanks 
 and beaches would be formed round its shores as it 
 gradually sank, and though the gravels would be re-distri- 
 buted, the larger stones, teeth, and bones would not be 
 destroyed, but would be scattered over the submerged 
 surfaces. It is indeed possible that some of the remains 
 are those of animals which were left on the island at the 
 time of its separation from the Continent, and were alive 
 when the final and complete submergence took place. 
 
 By the phenomena of the Dogger Bank, therefore, we 
 are led to look back to a time when it was neither a bank 
 nor an island, but a portion of western Europe, its southern 
 and western sides being washed by the waters of a large 
 river, which drained a large region to the south of the 
 bank and flowed northwards along what is now the deeper 
 part of the North Sea. In point of fact, a consideration 
 of all the evidence brings us to the conclusion that the 
 North Sea had then no existence, and that the western 
 coast-line of Europe ran outside our islands somewhere 
 between the contour-lines of 40 and 100 fathoms. It was 
 the opinion of Godwin-Austen, De la Beche, Lyell, and 
 nearly all subsequent writers, that the 100-fathom contour 
 should be taken as the coast-line of this period, but there 
 is no proof that the elevation was quite so great, and in 
 
296 NEOZOIC TIME. [CHAP. XIII. 
 
 Plate XIV. I have taken the line of 80 fathoms (480 feet) 
 as the extreme limit, though it does not make much 
 difference with respect to the extent of the land which line 
 is taken. As stated already, the river flowing through 
 the North Sea was the Ehine, the Thames, Ouse, and all 
 other British rivers which now flow into that sea being its 
 tributaries. 
 
 The English Channel was a wide valley through which 
 the united waters of the Seine and Somme, with many 
 tributaries from southern England, ran westward to the 
 Atlantic. The Bristol Channel was a similar valley watered 
 by a continuation of the river Severn, and opening west- 
 ward on to a vast plain which lay to the south of Ireland. 
 Thus Professor Dawkins, alluding to a cave on Caldy 
 Island off the coast of South Wales, in which numerous 
 remains of large mammalia have been found, remarks, 
 " It may, therefore, be reasonably concluded that when 
 they perished in the fissures Caldy was not an island, but 
 a precipitous hill overlooking the broad valley now occupied 
 by the Bristol Channel, but then affording abundant 
 pasture. We must, therefore, picture to ourselves a fertile 
 plain occupying the whole of the Bristol Channel, and sup- 
 porting herds of reindeer, horses, and bisons, many ele- 
 phants and rhinoceroses, and now and then being traversed 
 by a stray hippopotamus, which would afford abundant 
 prey to the lions, bears, and hyaenas inhabiting all the 
 accessible caves, as well as to their great enemy and de- 
 stroyer Man." 
 
 St. George's Channel and the Irish Sea formed another 
 large area of low-lying ground, the centre of which, as 
 already mentioned, was occupied by a long but compara- 
 tively narrow lake ; this lake received the waters of all the 
 rivers which drained the surrounding parts of Ireland, 
 Wales, England, and Scotland, and the Admiralty charts 
 show that the excurrent river ran from its southern 
 
CHAP. XIII.] PLEISTOCENE EPOCH, 297 
 
 extremity and joined that which traversed the Bristol 
 Channel. 1 
 
 The great lake in the Irish Sea was not the only one 
 which existed on the great tracts of undulating ground 
 which surrounded the more hilly districts of Great Britain 
 and Ireland. Many other lakes existed off the west coast 
 of Scotland, the sites of these being indicated by the areas 
 of deeper soundings. 2 Others appear to have existed in the 
 English Channel and in the bed of the North Sea, but 
 some of these are probably portions of the ancient river 
 valleys, and are now hollows because of the unequal 
 distribution of detritus over the sea-floor, or because they 
 are exposed to the scour of currents. 
 
 How long the land remained at such a high level we 
 cannot say, but there are reasons for thinking that physical 
 changes of considerable magnitude occurred in the northern 
 districts, while little change took place in the physical con- 
 dition of southern England ; the record of these changes, 
 however, has not yet been satisfactorily deciphered. The 
 union of Ireland to England and of England to France and 
 Belgium seems to have continued throughout the later 
 Pleistocene period ; it lasted long enough for Palaeolithic 
 man to be supplanted by Neolithic man, and for a large 
 number of mammalia to become extinct. 
 
 There is, however, good reason to believe that during 
 the immigratioQ of the existing fauna into Britain a 
 gradual subsidence of the whole region was taking place, 
 
 1 In the map given by Professor B. Dawkins ('-'Early Man in Britain/' 
 p. 150) the Irish Sea is made by some oversight to drain northward 
 instead of southward ; but an inspection of the reduced Hydrographic 
 Chart of the British Isles shows that there is a continuous ridge 
 between Mull and Malin Head where the soundings are under 40 
 fathoms, and which must have formed a watershed under the conditions 
 assumed. 
 
 a See map in J. Geikie's " Great Ice Age," and chap, xxiv., second 
 edition. 
 
298 NEOZOIC TIME. [CHAP. XIII. 
 
 and that by this subsidence Ireland was first of all separated 
 from England, and then a little later on England was 
 severed from the Continent. This gradual severance before 
 the complete establishment of the European fauna in our 
 islands seems to be indicated by the peculiar distribution 
 of species, and especially of the mammals and reptiles, at 
 the present time. This was first pointed out by Professor 
 E. Forbes, and has been more fully investigated by Mr. 
 A. E. Wallace, 1 who gives the following figures : 
 
 Germany has 90 species of Mammalia. 
 
 Britain ,,40 
 
 Ireland 22 
 
 Belgium has 22 species of Eeptilia and Amphibia. 
 
 Britain 13 ,, 
 
 Ireland 4 
 
 We must suppose, therefore, that the land did not 
 remain very long at the elevation shown in Plate XIV., 
 and that the connection between England and Ireland 
 was soon reduced to the condition of an isthmus, which 
 was submerged before more than four out of the twenty- 
 two continental species of reptiles had crossed in sufficient 
 numbers to effect a permanent settlement in Ireland. 
 Measured in number of years the time taken to effect 
 this may have been long, but geologically speaking it 
 was short. Ireland then became an island, while England 
 still remained a part of the Continent, and there was 
 doubtless a time when the line of 40 fathoms formed the 
 coast-line of Britain, and when the geography was such 
 as is represented in Plate XV., which shows the area that 
 would be converted into land by an upheaval of 40 fathoms 
 (240 feet) at the present time. 
 
 The coincidence of the coast-line with the 40-fathom 
 line was, however, only an epoch in the history of the 
 1 " Island Life," p. 319 et scq. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 299 
 
 subsidence ; the downward movement continued, and the 
 area of land was gradually reduced, the sea advanced 
 further and further up the valley of the English Channel 
 and over the plain of the North Sea, till at length the 
 plateau of the Dogger Bank was converted into an island, 
 and the waters met across the watershed which we now 
 call the Straits of Dover. As above mentioned, we may 
 infer that the final separation of England and France took 
 place before all the wild animals which now exist in Europe 
 had reached the western coasts of that continent, or at any 
 rate before they had occupied the British area in such 
 numbers as to become permanent colonists. 
 
 It was probably to this subsidence, and the changes of 
 geography and climate which it brought about, that the 
 extinction of the mammoth and its associates was due. It 
 must be remembered that the fauna associated with Neo- 
 lithic man is a direct continuation of the fauna of Palaeo- 
 lithic time, the differences consisting only in the absence 
 of certain species (by extinction or migration) and in the 
 presence of certain domesticated animals introduced by 
 man. 
 
 We now come to the phenomena of buried forests, and to 
 the consideration of the final movements which brought 
 about the existing relations of sea and land. In the first 
 place, I would deprecate the use of the term "Forest 
 period " in the sense of any special and distinct Post-glacial 
 epoch. Europe was doubtless clothed with forests through- 
 out the Pleistocene period wherever and whenever con- 
 ditions were suitable for the growth of forest trees ; in all 
 probability, too, dense forests nourished in the southern 
 part of England during the time of its occupation by 
 Palaeolithic man, and at any rate during the whole period 
 of subsidence which has been described above. The relics 
 of the ancient forests which are now found beneath our 
 bogs and fenlands, and at various levels around our coasts, 
 
300 NEOZOIC TIME. [CHAP. XIII. 
 
 can hardly be referred to one and the same period of time ; 
 some are undoubtedly much older than others, and as 
 Professor B. Dawkins has suggested, those which contain 
 remains of the mammoth are probably much older than 
 those which contain the bones and tools of Neolithic man. 1 
 
 It is quite possible that some of the submerged forests 
 date back to a time before the severance of England 
 from France, and that Neolithic man made his way dry- 
 shod across the valley of the Channel, but Professor 
 Dawkins believes that he crossed in canoes after the forma- 
 tion of the Straits of Dover. On this point we must wait 
 for further evidence. All the forests of which we have 
 knowledge at present would stand above the sea-level if the 
 land were raised 70 feet, and even allowing for the con- 
 sideration that such trees would not grow to such dimen- 
 sions on the sea-coast, it is not necessary to suppose that 
 England was then more than 90 feet (or 15 fathoms) above 
 her present level. 
 
 Neither is there any valid reason for supposing that 
 Scotland was then higher and more extensive than it would 
 appear if the sea-level coincided with the contour of 15 
 fathoms. The latest deposits assigned to the Glacial 
 period are unquestionably marine ; upheaval ensued, but 
 there is no geological evidence to show that Scotland 
 attained any very great elevation before subsidence again 
 ensued. Professor J. G-eikie has indeed suggested that 
 this was a second continental period, and has designed a 
 map of Europe in the " Forest period," 2 on the assumption 
 that the coast-line north of Scotland coincided approxi- 
 mately with the line of 500 fathoms, and that the Faroe 
 Islands were thus united to Scotland. The chief reason 
 he gives for such an extraordinary elevation of British 
 land at a time so little removed from the present is the 
 
 1 " Early Man in Britain," 1880, p. 255. 
 
 2 In " Prehistoric Europe." 
 
PLATE XV. PLEISTOCENE GEOGRAPHY, COAST-LINE COINCIDING WITH THE 
 
 CONTOUR OF 40 FATHOMS. 
 The inner blue line round England, France, and part of Ireland, is the line of 15 fathoms. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 301 
 
 difficulty of understanding bow the existing flora of the 
 Faroe Islands, which is of Scandinavian origin, could have 
 reached them without a land connection with northern 
 Europe in Post-glacial times. Mr. A. R. Wallace, however, 
 has shown that the distribution of plants can be effected 
 by other means than those necessary for the distribution 
 of terrestrial animals, and that it is very unsafe to draw 
 inferences from island floras similar to those which may 
 be drawn from their mammalian faunas. His remarks on 
 the flora of the Azores ] are very convincing, and he con- 
 cludes with saying that, " we have in such facts as these a, 
 complete disproof of the necessity for those great changes, 
 of sea and land which are continually appealed to by those 
 who think land connection the only efficient means of 
 accounting for the migration of animals and plants." 
 
 The Scandinavian character of the Faroe flora can be 
 explained by other means than the great elevation which 
 would have been required to unite it to Scotland, and we 
 may therefore dismiss Professor G-eikie's view of the geo^ 
 graphy of this period as quite unwarranted by the facts, 
 which are known to us. Professor Dawkins stands on 
 safer ground when he assumes that the coast-line during 
 the occupation of Britain by Neolithic man coincided 
 roughly with the 10-fathom contour, but, as already stated* 
 there is good reason for believing that some of the Cornish 
 forests date from a time when the sea did not reach beyond 
 the line of 15 fathoms, and whether the Neolithic invasion 
 took place under these geographical conditions, or at an 
 earlier epoch, it is certain that there was a time when the 
 position of the English and French coasts was approxi-. 
 mately that indicated by the inner line on the map x 
 Plate XV. 
 
 It is equally clear that in the south of England subsidence 
 
 1 " Island Life," 1880, p. 479. 
 
302 NEOZOIC TIME. [CHAP. XIII. 
 
 continued, and that the sea encroached farther and farther 
 on the forest-clad land, the submerged levels being covered 
 with a greater or less thickness of marine clays and sands, 
 while the valleys were converted into estuaries and filled 
 with thick accumulations of alluvial mud. These are the 
 conditions which now exist on our southern and south- 
 eastern shores ; everything points to a recent submergence, 
 with pauses during which peat beds were formed, and 
 there is no evidence of any more recent upheaval. 1 Similar 
 phenomena occur as far north as Lancashire and the south 
 of Yorkshire, but are not found much farther north. I 
 am informed by Mr. Hugh Miller that on the east coast 
 north of Durham there is no proof that the valleys have 
 ever been cut to a lower level, since the Glacial period, 
 than their present depth ; and when we reach the Forths 
 of the Forth and Clyde the phenomena connected with 
 valley erosion are altogether different. There are buried 
 forests, and they are covered by marine alluvial clays, but 
 the forests seldom run below low-water mark, and the 
 marine clays are now raised high above it, forming wide 
 plains or " carse-lands " from 30 to 45 feet above mean 
 sea-level. 
 
 In Scotland, therefore, it is clear that the last movement 
 was one of upheaval, and it would appear that this up- 
 heaval was contemporaneous with or later than what we may 
 call the Neolithic subsidence of England, for the Carse- 
 clays contain relics of Neolithic man. If the last movement 
 which our islands have experienced had been similar 
 throughout their extent, England would have had her 
 carse-lands, and the lower tiers of raised beaches which 
 
 1 The raised beaches of Brighton, Selsea, Portland, and the Cornish 
 coasts are generally regarded as much older than the submerged forests. 
 They probably date from the previous elevation (Palaeolithic time), and 
 must not be confounded with the 25 and 50-feet terraces of the Scottish 
 coast. 
 
CHAP. XIII.] PLEISTOCENE EPOCH. 303 
 
 occur on the Scottish shores would have been traceable 
 along the rocky coasts of Wales and Ireland. As a matter 
 of fact, the lowest or 25-feet beach descends to lower and 
 lower levels along the east coast of Ireland, and coincides 
 with the present level of the sea in the neighbourhood of 
 Dublin. 
 
 We may therefore conclude that though the buried 
 forests of Scotland grew, like those of England, during a 
 period of subsidence, either this subsidence did not last 
 so long in the former country as it did in England, but 
 was succeeded by a reverse movement while the south of 
 England was still sinking, or else that after the subsidence 
 had affected both countries to the same extent, an upheaval 
 took place in Scotland while the greater part of England 
 and Ireland remained in a stationary condition. It is only 
 on one of these two suppositions that the phenomena of 
 raised beaches and buried forests in England, Scotland, 
 and Ireland can be satisfactorily accounted for. 
 
CHAPTER XIV. 
 
 SUMMARY OP THE GEOGRAPHICAL EVOLUTION OF THE 
 BRITISH ISLES. 
 
 T N this concluding chapter it is my intention to review 
 -^ the series of geographical mutations which have been 
 described in the preceding pages, to take note of the rela- 
 tive age of the diverse physical districts which make up 
 the British Islands, and to consider how far the geo- 
 graphical restorations which have been attempted can be 
 regarded as consecutive stages in the building and fashion- 
 ing of that part of north-western Europe which may be 
 called the British region, meaning by this term not only 
 the actual land-tracts which constitute Great Britain, 
 Ireland, and the adjacent islands, but also the narrow 
 seas which separate them from one another and from the 
 continent of Europe. 
 
 Geologists can hardly now subscribe to the Huttonian 
 dictum that no traces are to be found of a beginning in 
 the world's economy, but the glimpses which we have 
 obtained into the physical conditions of the earliest Cam- 
 brian epoch do not warrant us in attempting any definite 
 delineation of land and sea. Nor is our knowledge of the 
 succeeding Palaeozoic periods sufficiently complete to make 
 our reconstructions more than guesses at the truth. In- 
 deed, the geologist who is attempting to restore the geo- 
 graphy of any epoch of Palaeozoic time may be compared 
 to an archaeologist who is examining the ruins of a temple 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 305 
 
 which is so ancient as to be different from any previously 
 known, and who is endeavouring to restore the ground- 
 plan of the original building from the scanty fragments 
 which remain ; he observes a piece of wall here, a corner 
 of masonry there, a broken arch in one place, and a pros- 
 trate column in another ; he has to consider the probable 
 relations of these remnants to one another, and to evolve 
 a connected whole by imagining the position of the missing 
 parts. So the geologist finds indications of dry land in 
 one place, of deep sea in another, of an island here, and of a 
 long coast-line elsewhere, and he has to piece the puzzle 
 together and to supply the missing connections as best he 
 can with the knowledge at his command. 
 
 At present, therefore, the maps of early Palaeozoic geo- 
 graphies are only pictorial representations of the ideal 
 views which are suggested to our minds by the inferences 
 obtained from the study of a few small and disconnected 
 areas. This is more particularly the case with the geo- 
 graphical restorations of Cambrian, Ordovician, Silurian, 
 and Devonian times ; that of the Carboniferous period 
 does, indeed, stand on a wider and more trustworthy basis, 
 because various circumstances have contributed to put us 
 in possession of a more complete record of this period than 
 we have of those which preceded it, and we did therefore 
 pause to attempt a more detailed reconstruction of the 
 geography of the British region during the formation of 
 the Carboniferous Limestone. We may, perhaps, assume 
 that the restoration given in Plate IY. is so far approxi- 
 mately correct as to show the real connections of the seas 
 and the general outlines of the land areas of the period in 
 question. 
 
 We can, at any rate, say that certain districts which 
 form part of modern Britain were also portions of the 
 early Carboniferous land, and that they were then struc- 
 turally the same as they are now, so that as rock-masses 
 
 x 
 
306 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 they may be said to date from this period, or from that of 
 the Upper Old Eed Sandstone, which immediately pre- 
 ceded it. The greater part of Wales and Shropshire, with 
 tracts of rock which are now buried beneath newer strata 
 in the counties of Stafford, Warwick, and Leicester, form 
 one such district ; the Lake District of Cumberland and 
 Westmoreland is another ; the southern uplands of Scot- 
 land are a third, and the Scottish Highlands seem to have 
 formed part of a continent which also included certain 
 tracts in the north-west of Ireland. Land appears also to 
 have extended from the borders of Wales across the Irish 
 Sea, and to have included small portions of the eastern 
 sea-bord of modern Ireland. 
 
 But although we can truly say that the foundations of 
 our islands had been laid at or before the commencement 
 of the Carboniferous period, and though we can point to 
 certain districts which seem to be the worn-down remnants 
 of Carboniferous land-tracts, yet we must remember that 
 this period was a time when there was more land. than 
 water where the Atlantic Ocean now rolls, and when the 
 broad platform on which the British Islands now stand 
 did not exist ; it is true there was what might be termed a 
 British island, but it lay neither over England, Ireland, or 
 Scotland, the greater part of it occupying the place of the 
 sea which now divides them, while the continent to which 
 this island was subsidiary lay, not to the south and east of 
 it, but to the north and north-west of the British area. 
 Such a state of physical geography is so different from the 
 present order of things, that it would seem rather as if 
 the seas and continents of the Palaeozoic world had an 
 evolutional history of their own which culminated in the 
 geographical conditions of the Carboniferous period, than 
 as if we could treat this period as a phase in the evolution 
 of the existent oceans and continents of the world. But 
 whether such a view is correct or not, we know so little 
 
CHAP. XIV.] SUMMARY OP GEOGRAPHICAL EVOLUTION. 307 
 
 about the sequence of the great physical changes which 
 ensued in later Carboniferous and in Permian times that 
 we are hardly in a position to take the early Carboniferous 
 geography as the starting point for any connected evolu- 
 tional history of the British Islands. 
 
 To the Carboniferous succeeded a great transitional 
 period, during which immense geographical changes seem 
 to have taken place throughout the northern hemisphere. 
 In Britain this is represented by two great stratigraphical 
 breaks with an intercalated group of peculiar deposits, and 
 opinion is divided whether the greatest physical changes 
 took place before or after the formation of these Permian 
 or Dyassic deposits. For our present purpose we may 
 regard the whole as one period, and the final pre-Triassic 
 movements may be considered as the culminating effort, 
 as it were, of the disturbing forces which had been set in 
 action at the close of the Carboniferous period, and which 
 seem to have acquired unusual power and energy from the 
 state of tension induced by the long antecedent period of 
 quiet accumulation. 
 
 The general result was the formation of a large conti- 
 nental territory over the northern part of the European 
 area, and the platform on which the British Islands stand 
 formed part of this Triassic continent. Not only so, but 
 the regional blocks which form the more salient portions 
 of our islands had already been rough hewn, as it were, 
 and set up in the places which they now occupy to be 
 gradually carved and sculptured during the long Neozoic 
 ages into the forms and features which they now exhibit. 
 The principal hill-ranges of western and northern England, 
 of Ireland, and of Scotland, were then in existence, and 
 bore in most cases the same general relations to the lower 
 ground around them as they do at the present time. 
 
 It is true that the east of England bore a very different 
 appearance from its modern aspect, forming as it then did 
 
308 SUMMARY OP GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 part of a high rocky and mountainous region which 
 stretched eastward across the area of the North Sea, but 
 the gradual detrition, planation, and burial of this ancient 
 land can be deciphered from the record of the Mesozoic 
 rocks, and does not constitute any difficulty in the way of 
 tracing the geographical evolution of Britain out of that 
 part of the Triassic continent which covered the British 
 area. 
 
 It is conceivable that the progress of Geology may 
 enable some future student to restore the features and 
 outlines of the pre-Carboniferous land to the same extent 
 as we can now indicate those of the Triassic continent, and 
 by tracing the series of transformations which took place 
 in late Carboniferous and Permian times to describe the 
 processes which led to the growth of the great continents 
 that existed in the northern hemisphere at the beginning- 
 of Neozoic time. But even when this is done the Triassic 
 period will still form a new point of departure whence to- 
 follow the series of changes that occupied the long ages of 
 Neozoic time and culminated in the evolution of the 
 modern continents and oceans. 
 
 With the Trias, in fact, we reach a stage in the geo- 
 logical history of Europe from which we can start with a> 
 reasonable expectation of being able to describe the gradual 
 building up of that Pliocene and Pleistocene continent out 
 of which the British Islands have been carved. Let us, 
 therefore, commence with a brief review of the geography 
 of the British region in Triassic time. 
 
 The special features of the early Triassic land were the 
 broad plains and valleys which in the later part of the 
 period were converted into one long and branching lake- 
 basin, and which have left an impression on the physical 
 geography of Britain that has lasted to the present day. 
 The broadest of these plains lay over central England, and 
 was prolonged north-westward on the one hand through 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 309 
 
 Cheshire and Lancashire across the Irish Sea, and north- 
 eastward on the other hand through Nottingham, Lincoln, 
 and York, far into what is now the bed of the North Sea, 
 while to the southward a basin which seems to have been 
 always more or less filled with water occupied the southern 
 part of England and the central area of the English 
 Channel. 
 
 Between the two northern plains, and between the arms 
 of the great lake into which the low ground was subse- 
 quently converted, rose the mountain range which is now 
 known as the Pennine chain. This must have lifted its 
 crests and escarpments much higher above the flanking 
 low lands than it does at the present time ; we may sup- 
 pose that in those places where patches of the Lower Coal- 
 measures had escaped destruction and lay over the Mill- 
 stone grit the hills were nearly 2,000 feet higher than they 
 are now, that being the thickness of the grits and gan- 
 nister measures which once capped such table-lands as that 
 of the Peak country and Kinderscout. These hills may, 
 therefore, have risen to heights of between 3,000 and 4,000 
 feet above the surface of the plains. 
 
 Northward then, as now, the Pennine range widened out 
 and was continuous with the Cheviots and the southern 
 uplands of Scotland, the hilly country being penetrated by 
 many deep valleys the lower parts of which afterwards 
 became inlets of the great salt lake. Whether the Scottish 
 lowlands were lowlands then we do not know, but the 
 Highlands were certainly part of a mountainous region in 
 the hollows of which other lakes came eventually to be 
 formed. 
 
 To the westward of this central tract of country, with its 
 several lake-basins, lay a vast region of hills and 
 mountains, with possibly other plains and lakes, which 
 stretched westward into the Atlantic at least as far as the 
 present contour-line of 1,000 fathoms. Of this region 
 
310 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 Ireland, Wales, and the Ocrynian peninsula are the only 
 remnants, but these territories were doubtless then united 
 to one another, as well as to Brittany on the south and 
 to the Hebridean land on the north. 
 
 The country that lay to the south of the British lacus- 
 trine area was probably low and flat, though whether in 
 the condition of a steppe or of a desert-plain can hardly be 
 decided, though the close proximity of salt lakes makes it 
 probable that most of the surrounding land was either a* 
 rocky or sandy desert. To the eastward there appears to 
 have been another tract of high and rocky land separating 
 the lake-basin and the southern plains from those of 
 Germany and Eussia ; part of this high land lay over the 
 north-east of France, Belgium, and the east of England, 
 with the intervening portion of the North Sea area, but 
 whether it extended northward to the Scandinavian area,, 
 or was divided from that by desert plains connecting those- 
 round the salt lakes of Germany with the north-eastern 
 end of the British lake, we are unable to say from lack of 
 evidence. 
 
 Thus the picture which is presented to our mental view 
 as that of the British region at the close of Triassic time is 
 a dry and arid country, comprising rocky mountains, deep 
 valleys, desert plains and large lakes, the most important 
 sheet of water being apparently as salt, as clear and heavy,, 
 and as nearly lifeless, as the modern waters of the Dead 
 Sea or of the Great Salt Lake of Utah. 
 
 The next picture in our geological gallery is a very 
 different one, so far as local colouring and general environ- 
 ment are concerned : a magic touch has altered the character 
 of the soil, the humidity of the air, and the salinity of the 
 waters, so that the land supports a luxuriant vegetation,, 
 and the waters, now those of an open sea, swarm with 
 creatures of various kinds. But the geographical change 
 which produced such great climatic effects was a com- 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 311 
 
 faratively small one ; it was simply that the subsidence of 
 the land, which probably had been in progress for some 
 time, led at last to the submergence of the French Triassic 
 plains beneath the waters of the Liassic sea, which thus 
 obtained access to the British area and converted the 
 Triissic lake into a gulf of that sea. 
 
 So far as we can tell, the geography of Liassic Britain 
 was precisely the same as in Triassic time, except that the 
 site of the great lake was occupied by a sea which opened 
 southward, and probably that the area covered by water 
 was somewhat larger. The position of the land- tracts was 
 not, so far as we know, otherwise altered, but they were 
 probably exposed to more rapid processes of surface dis- 
 integration, and the removal of material from higher to 
 lower levels was correspondingly accelerated. 
 
 Neither was this geographical arrangement materially 
 altered during the formation of the sands and limestones 
 of the Middle Jurassic series. We find proofs, however, in 
 certain portions of this series that large rivers were in 
 existence and poured large quantities of material into the 
 sea, so as to fill up portions of it and convert them into 
 shallow bays surrounded by tracts of swampy alluvial land. 
 Further, it would appear that subsidence ceased for a time, 
 and that some portions of the sea-bottom were raised 
 while other parts remained stationary, the result of these 
 movements being the formation of several distinct basins 
 separated from one another by submarine ridges like those 
 of the Mediterranean Sea ; one of these ridges was a pro- 
 longation of the Mendip uplift, and another crossed the 
 central part of England. 
 
 The period of the Upper Jurassic clays was one of 
 general and extensive subsidence ; there can be little doubt 
 that during their deposition the coast-lines were carried 
 backward and the area of the sea was greatly widened, but 
 how far this recession continued, and how much of the 
 
312 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV 
 
 surrounding land was submerged at the time of greatest 
 depression, are points upon which we must be content to 
 confess our ignorance. The greater part of England wa 
 probably submerged, but the submarine ridge which 
 stretched across the central part of the sea still influenced 
 deposition, for only 500 feet of sediment was deposited over 
 it during Upper Jurassic time, while the southern basins 
 received from 1,300 to 2,000 feet, and the northern lasin 
 about 1,000 feet of sediment (in Yorkshire). Possiblj this 
 unequal distribution of material reacted on the initial 
 cause, and the intervening ridge was kept from sinking to 
 the same extent as the basins on either hand Ijy the 
 pressure arising from the weight of the sediment poured 
 into those basins. However this may have been, it is 
 certain that the whole sea-bed was not levelled up when 
 subsidence ceased and upheaval set in, for it was the 
 central ridge which first became land and formed an 
 isthmus separating the northern and southern gulfs of the 
 Portlandian Sea (see Plate VIII.). The southern gulf 
 being the deepest, this remained in the form of a large 
 lake when the rest of the Jurassic sea-bed was converted 
 into the Purbeck and Wealden land. 
 
 The land of early Cretaceous times therefore differed in 
 some important particulars from that of the Trias. The 
 western arm of the Triassic lake and Jurassic sea became 
 a broad and fertile plain which opened south-eastward on to 
 a still wider and probably slightly higher undulating tract 
 of country, the watershed of which stretched across what 
 are now the Midland counties to the eastern tract of Palaeo- 
 zoic rocks, which we may call the eastern uplands. Whether 
 these uplands were originally as lofty as the mountains 
 which lay to the west of the Jurassic sea we have no means 
 of knowing, but it would certainly appear that their com- 
 parative elevation in Cretaceous times was very much less 
 then it had previously been. Either the post-Jurassic up- 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 313 
 
 heaval was greater in the western than in the eastern part 
 of the British region, or the later Cretaceous subsidence was 
 deeper in the eastern area ; it is very likely indeed that 
 both movements contributed to the same result, i.e. of re- 
 ducing the whole eastern tract to a lower relative level than 
 it had occupied throughout Jurassic time. 
 
 The early Cretaceous subsidence seems to have been 
 fairly equable, and the Vectian sea does not seem to have 
 encroached much on these eastern uplands, though it is 
 probable that the relative levels of the two areas were so 
 far altered that the sea covered a wider tract on the east 
 and a much narrower one on the west than would have 
 been submerged by a depression of the same vertical extent 
 in Jurassic time. In the succeeding epoch this was cer- 
 tainly the case, and we know that the whole of eastern 
 England sank below the waters of the Gault sea, while 
 there is good reason to believe that this sea did not extend 
 to Wales or over the north-west of England. The subse- 
 quent subsidence, however, was much more extensive ; not 
 only did it bury the remaining portions of the eastern land 
 under a continuous sheet of Chalk, but the western land 
 was converted into an archipelago, and great sheets of chalk 
 and greensand were deposited far beyond the limits of the 
 Jurassic strata over the slopes of the western and northern 
 highlands. 
 
 The chief result of these changes therefore, so far as the 
 geographical evolution of Britain is concerned, was the 
 complete suppression and burial of the rocky land which 
 had previously existed over the areas now occupied by the 
 North Sea and the eastern counties of England. This land 
 has never again been uncovered, and its extent has only 
 been gradually revealed to us by the deep borings which 
 have been made in England, France, and Belgium. Its 
 coverings were indeed repeatedly added to in Tertiary 
 times, while erosion was busy over the rest of England. 
 
314 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV, 
 
 The evidence on which to found any conclusions as to 
 the aspect of the country when it emerged from the waters 
 of the Cretaceous sea is of the slenderest, but we may as- 
 sume that England, Scotland, and Ireland were bound 
 together into one mass of land, and that the water- spaces 
 which now separate our islands were then filled up by a> 
 greater or less thickness of Jurassic strata, covered and 
 levelled up by wide- spreading sheets of greensand and 
 chalk. The Atlantic sea-bord then lay considerably to 
 the west of our islands, re-occupying a line along the sub- 
 marine slope which now plunges from 100 to 1,000 fathoms. 
 There is good reason to suppose that there were land con- 
 nections, on the one hand between Scotland and Green- 
 land by way of the Faroes and Iceland, and on the other 
 between Scotland and Scandinavia, thus completely isolat- 
 ing the Arctic Ocean and preventing any influx of cold 
 northern currents into the Atlantic or west European seas. 
 On the south-west also there would appear to have been a 
 continuous tract of land uniting Ireland and Wales with 
 Brittany and the central part of France. 
 
 During the progress of the Eocene period the south-east 
 of England came alternately under the influence of an 
 eastern and a southern sea, but the delimitation of these 
 two seas is one of the most difficult problems of Tertiary 
 geography. With the evidence at our command it is im- 
 possible to say in which direction the great gulf whose 
 waters covered so much of England and Belgium in the 
 time of the London Clay communicated with the open 
 sea ; the probabilities are much against any northward 
 opening ; there is no trace of an easterly one, while the de- 
 posits of Lower Eocene age seem to thin out and disappear 
 in westerly, southerly, and south-easterly directions. The 
 difficulty is in fact such as to raise a doubt whether the 
 accepted views of the correlation of the French and Eng- 
 lish Eocenes are altogether correct. During the formation 
 
CHAP. XIV.] SUMMAET OF GEOGRAPHICAL EVOLUTION. 315 
 
 of the Upper Eocenes (or Nummulitic series) the seas 
 which covered parts of England certainly opened southward 
 into a great southern or Mediterranean sea, whence per- 
 haps we may conclude that the sea of the London Clay 
 had a similar but narrower opening in the same direction. 
 
 In Oligocene time the western and southern European 
 seas were greatly contracted, but a shallow northern sea 
 was gradually formed which extended over south-western 
 Russia, Prussia, Holland, and Belgium, but does not 
 appear to have reached quite so far west as England. 
 There was, however, a smaller and possibly isolated sea, 
 lying over northern France, and receiving the waters of a 
 large river which drained the western part of the British 
 region and had its estuary over Hampshire and the Isle of 
 Wight. 
 
 Even after the early Miocene upheaval, and when subsi- 
 dence again led to the formation of deposits in France and 
 Belgium, the sea seems to have re-occupied portions of the 
 same basins, for the Miocene and early Pliocene beds occur 
 in similar positions and in the same localities as those of 
 Oligocene age. It is true that the sea of the Diestian Sands 
 spread westward into the east of England, and that the 
 precise limits of this sea are very doubtful, but there is no- 
 proof that it had any great northerly extension, or that the 
 belt of land enclosing the Arctic Ocean had as yet been 
 broken through either to the north or east of Scotland. 
 
 But while the eastern and southern portions of the 
 British region were receiving here and there fresh acces- 
 sions of stratified material, a very different process was in 
 operation over the western and northern portions of the 
 same region. There can be little doubt that these districts 
 remained in the condition of dry land throughout the 
 duration of the Eocene, Oligocene, Miocene, and Pliocene 
 periods, and that their surface was profoundly modified by 
 the continued action of rain, frost, and running water. 
 
o!6 SUMMARY OP GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 From the fragments of terrestrial surfaces preserved be- 
 neath the Eocene lavas of Ireland and the Western Isles, 
 we know that rivers were actively engaged in carving 
 channels out of the Secondary rocks which surrounded the 
 volcanic district, and that during the course of the Eocene 
 period a large amount of material must have been carried 
 ;seaward by these streams. 
 
 Further, if we may assume that the plateau of Antrim is 
 still approximately in the same position which the whole 
 volcanic district originally occupied with regard to the sur- 
 rounding country, we may infer that the rest of the plain 
 or plateau over which the lavas were poured has since sunk 
 considerably below this level ; we may suppose, in fact, that 
 when the volcanic activity finally ceased, large parts of the 
 .area began to sink inwards, the subsidence being greatest 
 to the west of Scotland. This conclusion is confirmed by 
 the actual proofs of inward subsidence round the volcano 
 of Mull, as observed by Professor Judd, by the inclined 
 position of the lavas of Skye and Eaasay, and by the exis- 
 tence of powerful post-Eocene faults which have dropped 
 portions of the volcanic masses below their original level. 1 
 To this local subsidence we may attribute the great depres- 
 sion which is now filled by the waters of the Minch and the 
 Sea of the Hebrides, large parts of which are deeper than 
 the outer plateau on which the Hebrides stand, and would 
 form extensive lakes if the whole region were raised to the 
 extent of 500 or 600 feet. 
 
 We have no further record of the progress of the great 
 denudation which was continued uninterruptedly through 
 Eocene, Oligocene, Miocene, and older Pliocene times, but 
 we know that it resulted in the removal of all the Creta- 
 ceous and Jurassic rocks (except the few remnants which 
 .survive), together with large portions of the Trias from 
 
 1 "Quart. Journ. Geol. Soc.," vol. xxx. p. 257, and vol. xxxiv- 
 jpp. 673, 671. 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 317 
 
 the west of Scotland and from the area of the Irish Sea, as- 
 well as from the north-western counties of England. Por- 
 tions of the older Neozoic rocks were doubtless removed 
 during the earlier part of the Cretaceous period, but the 
 greater part of the work was doubtless accomplished in 
 Tertiary times. 
 
 With regard to the formation of St. George's Channel 
 between Wales and Ireland we have very little evidence to 
 guide us, but it may have originated in a minor valley 
 like that of the Clwyd in North Wales opening northward 
 into the basin or plain of the Irish Sea. All the proba- 
 bilities and analogies of the case lead us to conclude that 
 its origin was post-Carboniferous and pre-Cretaceous, and 
 that Wales was completely isolated during the great Creta- 
 ceous subsidence. We may therefore assume with much 
 reason that a chalk-filled channel (narrower of course 
 than the present one) existed at the beginning of the 
 Eocene period, and that during the course of the ensuing 
 epochs it was re-excavated by subaerial agencies and 
 widened to nearly its present dimensions. 
 
 In the south of England also great changes were in pro- 
 gress during the interval between Eocene and Pliocene 
 times ; the curvature of the London and Hampshire basins 
 was completed, and the intervening Wealden axis was 
 largely denuded of its original coverings, receiving its final 
 planation from the waves of the older Pliocene sea. Thence 
 it emerged to form a tract of elevated land 600 or 700 feet 
 above the sea-level of newer Pliocene time, and stretching 
 continuously across the Straits of Dover through the north 
 of France to the region of the Ardennes. 
 
 We now arrive at another important epoch in the 
 development of British geography, the time which is 
 indicated by the break between the older and newer Plio- 
 cene deposits, and during which the movements that led to 
 the formation of the North Sea basin appear to have taken 
 
318 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 place. These movements, so far as we can judge, produced 
 the geographical conditions represented in Plate XIII., Bri- 
 tain then forming a broad and roughly triangular promon- 
 tory based on the northern part of France and ending 
 northwards beyond the Shetland Isles. The western coast- 
 line lay probably between the contours of 200 and 300 
 fathoms, at any rate off the north-western coast, so that 
 the isthmus between Scotland and the Faroe Isles was 
 completely submerged. The eastern coast, however, along 
 the western border of the newly-formed North Sea, ap- 
 proximated closely to the outline it now presents. 
 
 Before the close of the period, indeed, the agencies 
 which had been busily and continuously engaged through- 
 out the whole of antecedent Tertiary time in modelling 
 and carving the surface of the British region, had almost 
 completed their task. All the principal physical features 
 of our islands had then been developed, and the general 
 aspect of Britain in later Pliocene time can hardly have 
 differed very much from that of modern Britain, except that 
 it stood bodily higher above the level of the ocean, so that 
 the seas and channels which now separate our islands from 
 one another and from France were then in the condition 
 of fertile plains and valleys. In minor details there was 
 of course a considerable difference ; the North Downs, and 
 probably also the South Downs, were continuous across 
 what is now the head of the English Channel, and the 
 surface features of the country, in the absence of the 
 superficial clays and gravels which now cover such large 
 areas, must necessarily have had a different aspect. 
 
 The Pliocene surface had of course its terrestrial and 
 fluviatile deposits ; the long-continued action of wind, 
 frost, rain, and rivers must have resulted in the formation 
 of long slopes of debris among the hills, of thick deposits 
 of sand and gravel in the valleys, of deep beds of clay and 
 marl in the lake-basins, and in the production of a thick 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 319 
 
 mantle of soil over other parts of the land. Such was the 
 state of Britain at the beginning of that remarkable epi- 
 sode which is known as the Glacial Period ; when snow 
 began to accumulate on the mountains and to form 
 glaciers which crept farther and farther down the valleys. 
 By these advancing ice-ploughs the higher parts of the 
 country were swept clean of all surface accumulations, the 
 materials being carried down to lower levels and ulti- 
 mately worked up into the Glacial Boulder- clays, gravels, 
 and loams. 
 
 The uncertainty which exists with regard to the real 
 succession, and to the precise mode of formation of these 
 Glacial deposits, makes it unsafe to attempt a geographi- 
 cal restoration of any of the several phases of the Glacial 
 epoch. It would be easy to follow Professor J. Geikie and 
 Professor Hull, and to give a pictorial representation of a 
 huge ice- sheet covering nearly the whole of Britain and 
 Ireland, but the accuracy of such a picture depends on the 
 assumption that every district where ice-marks and Boulder- 
 clays occur was simultaneously covered by one continuous 
 mass of ice. 
 
 There are, however, indisputable proofs that the whole 
 country sank from a position of considerable height above 
 the sea to one of 1,800 or 2,000 feet below its present 
 level, and it has been thought that these conditions could 
 be represented by a map showing the archipelago of 
 islands that would remain above water if the British Isles 
 were now submerged to that extent. But to omit ice from 
 such a map is to omit one of its most important features, 
 for there is good reason to suppose that the extent and 
 thickness of the Scottish ice was such as to keep the sea 
 from ever being in contact with Scottish ground above a 
 level of 550 feet, so that the greater part of Scotland was 
 practically unsubmerged when the contour of 2,000 feet 
 was the coast-line of Wales. 
 
320 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV, 
 
 Leaving these problems for future solution, we must 
 pass to the time when the rigour of the Ice Age had mode- 
 rated, and when the British region had emerged from the 
 Glacial sea ; when the land-ice had retreated to the moun- 
 tain-valleys, and had left the lowlands free of ice and 
 snow, though covered with the thick mantle of Boulder- 
 clay and gravel which was the gift of the Glacial period. 
 The movement of upheaval continued till Britain again, 
 stood high above the sea and was united to the Continent 
 across the valley of the English Channel and the plains of 
 the North Sea. 
 
 This phase of Pleistocene geography is represented in 
 Plate XIV., and on comparing it with that of the Pliocene 
 in Plate XHI. it will be observed that the chief difference 
 is in the relative level of the floor of the North Sea. In 
 Pliocene times this area was below the sea-level, though the 
 general level of the land was higher then than in the later 
 period ; but the cause of this difference is probably to be 
 found in the large quantities of detritus which must have 
 been carried into this sea by the Scottish and Scandinavian 
 ice, and which must have buried the Pliocene sea-bed 
 under several hundred feet of ice-borne material. A recent 
 boring at Utrecht has proved that the surface of the Plio- 
 cene deposits is more than 500 feet below that part of 
 Holland, and, as the Pliocene sea probably deepened north- 
 ward, it is therefore hardly too much to assume that 
 the same surface lies some 100 fathoms below the pre- 
 sent bed of the North Sea between Norway and Britain, 
 and consequently that the upheaval necessary to convert 
 this sea into land after the Glacial Period was 100 fathoms 
 less than would have been required to effect the same 
 result in later Pliocene time. 
 
 The sea-beds on the western side of England and Scot- 
 land were doubtless shallowed in a similar manner, and 
 even on higher ground many of the Pliocene valleys were 
 
CHAP. XIV. 1 SUMMARY OP GEOGRAPHIC 
 
 completely masked and buried beneath the Grlacial de- 
 tritus, so that the Pleistocene rivers were compelled to 
 make fresh channels for themselves, and it was not there- 
 fore till this time that our present river-system was per- 
 fected. So long as the British coast-line lay near the con- 
 tour of 80 fathoms our modern streams were but tribu- 
 taries of the three great rivers which ran outside the present 
 limits of Great Britain, that to the east being a continua- 
 tion of the Rhine, that to the south a prolongation of the 
 Seine, and that to the west a river to which no modern 
 name could be applied, but of which all the rivers of 
 western England, southern and eastern Ireland, were the 
 tributaries. 
 
 It was not long, however, before a reverse movement set 
 in, and subsidence caused a rapid recession of the coast- 
 line ; the North Sea crept southward over the plains be- 
 tween England and Holland, while the Atlantic crept 
 round Ireland and up the valley of the English Channel 
 till only a narrow isthmus separated England from France. 
 The Straits of Dover doubtless mark the position of the 
 lowest part of the watershed between the river-systems of 
 the Rhine and the Seine during the progress of this sub- 
 sidence. It is not unlikely that the actual straits are the 
 site of a valley formed by a river which ran northward, 
 nearer France than England, and cut through the northern 
 escarpment of the Chalk, as the Stour and Medway do at 
 the present day ; while a second stream ran south-west- 
 ward, nearer the British coast, and cut through the con- 
 tinuation of the South Downs east of Beachy Head. The 
 watershed between these two rivers is possibly marked by 
 the line of sandbanks which runs southward from the 
 Varne Bank and Colbart Ridge ; it would at any rate be 
 of no great elevation, and probably consisted of Weald 
 clay, like that between the rivers Wey and Arun at the 
 western end of the Wealden district. Subsidence under 
 
322 SUMMARY OF GEOGRAPHICAL EVOLUTION. [CHAP. XIV. 
 
 these circumstances would enable the sea to creep up the 
 valleys of the two rivers, and eventually to submerge part 
 of the low watershed between them ; waves and currents 
 would soon widen the breach, and have continued to widen 
 it from that time to the present day. 
 
 Thus was Britain finally separated from the Continent 
 to which it had been united throughout the greater part 
 of Tertiary time, and thus was the geographical evolution 
 of the British Isles at length accomplished; for though 
 certain minor changes took place after the formation of 
 the Straits of Dover, yet this severance of England from 
 the Continent gave Britain the geographical position she 
 now holds, and must therefore be regarded as the final act 
 in the long series of operations which conduced to the 
 building and fashioning of the British Isles. 
 
 Under the combined effect of subsidence and marine 
 erosion the British coast-lines continued to recede after 
 the formation of the Straits of Dover, but when after a 
 time the subsidence ceased, recession proceeded at a much 
 slower rate, and only along those shores which were ex- 
 posed to the direct action of currents, while the loss so 
 caused was partially counterbalanced by the silting up of 
 bays and estuaries. In Scotland, moreover, a vertical up- 
 heaval of nearly 50 feet resulted in an important accession 
 of land. The present outline of the British coast is there- 
 fore the outcome of all these minor operations, the balance 
 of gain and loss being apparently very nearly equal in the 
 case of Scotland, but decidedly on the side of loss in the 
 south of England. 
 
 Minor geographical changes are even now in progress, 
 and there is no reason to suppose that the present arrange- 
 ment of land and sea is the final geographical condition 
 of Europe, or that the British Islands will never again be 
 subjected to movements of upheaval and depression like 
 those which they have experienced in the past. It is very 
 
CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 323 
 
 probable, however, that the period in which we are now 
 living is one of those quiescent times which, as we have 
 seen, generally succeed periods of rapid movement and 
 disturbance. The earth's crust appears to be in a com- 
 paratively fixed and stable condition, and the movements 
 which are known to be in progress are so slight, or rather 
 the rate of change is so slow in relation to the short span 
 of human life, that we may safely rely on the permanency 
 of the present geographical conditions for a very long 
 period of future time. 
 
 Professor Prestwich arrives at a similar conclusion from 
 somewhat different premises. He thinks that the great 
 cosmical cold of the Glacial epoch accelerated the con- 
 traction of the earth's crust, and that the disturbances 
 consequent upon this contraction were greater during the 
 prevalence of this cold than in the immediately preceding 
 and succeeding ages ; that, therefore, " during a certain 
 number of years succeeding to and to be measured by the 
 length of the Glacial period (whether that be 10,000 or 
 20,000, or any other number of years), the disturbances of 
 the crust would be at a minimum, and its stability at a 
 maximum. This is the condition under which I conceive 
 the crust of the earth is now placed, and which, as I have 
 before suggested, ensures that state of repose and immo- 
 bility which renders it fit and suitable for the habitation 
 of civilized man." l 
 
 1 " Geology," by J. Prestwich, vol. ii. p. 549. 
 
CHAPTER XV. 
 
 THE THEORY OF THE PERMANENCE OF CONTINENTS 
 AND OCEANS. 
 
 IT seems only fitting that a study of the geographical 
 changes of the past, even though it is concerned with 
 no more than a small portion of a continent, should con- 
 clude with some expression of opinion regarding the de- 
 bated question of the permanence or permutation of 
 oceans and continents. 
 
 The theory of their permanence, that is to say, the view 
 that the position of the continents was fixed at the be- 
 ginning of geological time, and that oceans and continents 
 have ever since occupied their present relative positions, 
 was originated by Professor Dana, and has more recently 
 been independently maintained by Dr. A. R. Wallace and 
 Dr. A. G-eikie. 
 
 The theory of their permutation or interchange was 
 that held by Sir Charles Lyell and other geologists, who 
 regarded the continents and ocean-basins as great upward 
 and downward bendings of the earth's crust, and conse- 
 quently liable to shift their positions entirely in the course 
 of ages, so that what was once an ocean-bed might become 
 a continent, and vice versa. 1 
 
 The data on which Professor Dana bases his opinion are 
 entirely hypothetical ; it is, in fact, merely an inference 
 but a necessary and unavoidable inference from his 
 hypothesis of the manner in which the crust of the earth 
 
 1 " Principles of Geology," eleventh edition, vol. i. p. 258. 
 
CHAP. XV.] PERMANENCE OP CONTINENTS. 325 
 
 originally solidified ; and this inference must of course be 
 accepted or rejected, according as physicists may decide 
 upon the probability or improbability of the hypothesis 
 upon which it depends. Now this hypothesis is itself 
 based on the assumption that the earth was originally, and 
 is now, of unlike composition along different radii, or on 
 different sides ; the continental portions of the crust, 
 according to Professor Dana, being composed of denser 
 materials than the oceanic. 
 
 Mr. W. O. Crosby l has ably discussed this question ; he 
 points out that this initial assumption is entirely unsup- 
 ported by evidence, and that even if it were to be admitted, 
 Professor Dana's hypothesis involves so many other uncer- 
 tainties and improbabilities that it would not be worthy of 
 acceptance unless it was strongly confirmed by geological 
 evidence. 
 
 Dr. Wallace takes very different ground, and boldly 
 endeavours to support the theory of permanence by dis- 
 cussing the geological evidence, but he too has been 
 answered by Mr. Crosby (loc. cit.), by Mr. G-. S. Gardner, 2 
 and by Professor Hull. 3 
 
 Dr. Wallace's chief arguments, as stated in his " Island 
 Life," may be summarized as follows : 
 
 1. That the modern oceanic deposits are different from 
 any that occur among the rocks composing continental 
 land. 
 
 2. That the formations which compose our continents 
 are chiefly shore-deposits, and that the constant neigh- 
 bourhood of land is proved by the frequency of estuarine 
 and lacustrine deposits. 
 
 3. That formations of similar constitution and contem- 
 
 1 " Geol. Mag.," Dec. 2, vol. x. (1883), p. 241. 
 
 2 Ibid., Dec. 2, vol. viii. (1881), p. 241, and Dec. 2, vol. ix. 
 p. 546. 
 
 3 " Contributions to the Phys. Hist, of Brit. Isles," chap. iv. 
 
THE SUPPOSED PERMANENCE [CHAP. XV. 
 
 poraneous origin, and more than 150 or 200 miles wide, 
 seldom form part of continental land. 
 
 4. That the Chalk, though it is an extensive formation, 
 was formed in comparatively shallow water, the depth of 
 which would have been measured by hundreds and not 
 thousands of fathoms. 
 
 5. That no modern oceanic islands, except New Zealand 
 and the Seychelles, contain any Palaeozoic or Mesozoic 
 rocks, such as might be expected to occur in remnants of 
 old continental land. 
 
 To these arguments it is replied that : 
 
 1. The first statement is to a large extent true ; nothing 
 exactly like either the calcareous ooze or the red clays of 
 the modern ocean-beds has yet been found in the earth's 
 crust. It may be observed, however, that as a matter of 
 fact the limestones formed at one period of the earth's 
 history are seldom of exactly similar composition and 
 aspect to any formed at another period. Further, that the 
 resemblances between European Chalk and modern oceanic 
 ooze are so great that, allowing for a slight original diffe- 
 rence in the relative proportion of calcareous matter, and 
 for a certain amount of subsequent change, it must be ad- 
 mitted that the original condition of the Chalk was almost 
 identical with that of the ooze ; and, consequently, that it 
 was an oceanic deposit. This will be further discussed 
 under the fourth head. With regard to the red clay, even 
 if it is true that no such deposit does occur among strati- 
 fied rocks, this does not really prove more than that the 
 ancient oceans did not possess such abyssal depths as those 
 of the present day ; for the existence of this red clay seems 
 to depend entirely on depth and not on distance from land. 
 The existence of abyssal depths is surely not essential to 
 the idea of an ocean ; a wide expanse of comparatively 
 shallow water (i.e. under 1,000 fathoms) would be as 
 correctly called an ocean as a wide expanse of land which 
 
CHAP. XV.] OF CONTINENTS AND OCEANS. 327 
 
 did not anywhere rise to elevations of more than 6,000 feet 
 would be correctly called a continent. 
 
 2. As to the second statement, it is perfectly true that the 
 marginal belts of comparatively shallow water which have 
 always surrounded the tracts of continental land have been 
 from the earliest geological times the principal areas of de- 
 position. It would indeed be very surprising if it were 
 otherwise, for most of the materials carried down from 
 any tract of land must come to rest within a certain dis- 
 tance of the shore, and thus geological deposits are chiefly 
 shore deposits. Dr. A. G-eikie, however, goes farther, and 
 remarks that " the more attentively the stratified rocks of 
 the earth are studied, the more striking becomes the absence 
 of any formations among them which can legitimately be 
 considered those of a deep sea. They have all been de- 
 posited in comparatively shallow water." ] This also is 
 probably true if by comparatively shallow water Dr. 
 G-eikie means any depth not exceeding 1,000 fathoms. 
 Compared with the depth of modern ocean-troughs water 
 of only 700 or 800 fathoms is shallow, but it might fairly 
 be called a deep sea ; and, as. we shall presently see, there 
 is at any rate one formation which was probably formed in 
 a sea of at least that depth. 
 
 The absence or rarity of deep-sea deposits is in fact more 
 conspicuous among Palaeozoic than Neozoic rocks, but this 
 fact can hardly be taken as evidence of the fixity of oceans 
 and continents ; it would be more logical to regard the 
 absence of such deposits as evidence of the absence of 
 oceans, and to suppose that in these early times the relative 
 proportion of land was greater than it is now, or that the 
 arrangement of land and sea was such that neither covered 
 very large spaces of the earth's surface. 
 
 3. That Dr. Wallace should seriously argue that " de- 
 
 1 " Geographical Evolution, Proc. Roy. Geograph. Soc.," 1879, p. 426. 
 The italics are mine. 
 
328 THE SUPPOSED PERMANENCE [CHAP. XV. 
 
 posits uniform in character and more than 150 or 200 
 miles wide were rarely, if ever, formed at the same time " 
 (" Island Life," p. 101), is rather surprising when on a 
 previous page (p. 91) he quotes Sir Charles Ly ell's estimate 
 of the range of the Chalk beds of nearly uniform aspect 
 and composition extending from the north of Ireland to 
 the Crimea, a distance of about 1,140 geographical miles, 
 and in an opposite direction from the south of Sweden to 
 the south of Bordeaux, a distance of about 840 geographical 
 miles. 
 
 In point of fact, all that Dr. Wallace succeeds in proving 
 in Chapter VI. of his " Island Life " is that deep-sea de- 
 posits are of rare occurrence beneath the soil of modern 
 continents. This, however, is a very different thing from 
 proving a universal negative, which is what he sets himself 
 to do. It only amounts to this, that the conversion of even 
 a comparatively shallow ocean into continental land is a 
 stupendous operation, requiring many geological ages for 
 its accomplishment, and consequently that it has not 
 happened many times in the course of geological history. 
 
 4. The argument derivable from the differences between 
 Chalk and oceanic ooze has already been partially refuted, 
 but may now be more fully discussed. In the first place, 
 it is unreasonable to assume that the constituents of deep- 
 sea ooze, and the proportions of these constituents, should 
 have been just the same in the Cretaceous period as they 
 are now ; and, in the second place, it has been shown that 
 the differences between the two kinds of material is not so 
 great as Dr. Wallace supposed. It would appear that the 
 relative abundance of pelagic Foraminifera is largely de- 
 pendent on the temperature of the water, and that they 
 only occur in great abundance where the water is compara- 
 tively warm. This was especially remarked by M. Pour- 
 tales 1 with regard to the character of the deep-sea deposits 
 1 See " Geol. Mag.," vol. viii. 1871, p. 425. 
 
CHAP. XV.] OF CONTINENTS AND OCEANS. 329 
 
 off the eastern and southern coasts of North America, the 
 purely calcareous deposits being confined to the areas 
 warmed by the G-ulf Stream ; and the fact is confirmed by 
 the observations of Wallich, Carpenter, and Wyville Thom- 
 son. Now it is probable that the European Cretaceous sea 
 was considerably warmer than the present Atlantic, and con- 
 sequently it is not surprising to find a greater relative pro- 
 portion of calcareous matter in the Chalk. 
 
 Again, some beds of Chalk are very largely composed of 
 minute fragments of Inoceramus shell ; the molluscs which 
 formed these shells must have been very abundant on the 
 floor of the Chalk sea, but they have long been extinct, and 
 no mollusc with a similar shell is found abundantly on 
 modern ocean-beds ; consequently this kind of chalk has a 
 special composition, which is apparent under the micro- 
 scope, and which causes its chemical analysis to differ from 
 that of modern calcareous ooze. 
 
 But in spite of these and some other differences there is 
 sufficient resemblance between the analyses of the calcareous 
 ooze and of certain beds of Chalk to make it probable that 
 the original state of the latter was very similar to the pre- 
 sent state of the former. In the first place, we must re- 
 member that the calcareous ooze still retains its full pro- 
 portion of disseminated silica, whereas this silica has clearly 
 been abstracted from the greater part of the Chalk, and 
 has been concentrated into the flint nodules. If, therefore, 
 the ooze be compared with that part of the Chalk which 
 contains flints, the soluble silica should be deducted and 
 the proportions of the other ingredients re-calculated. 
 
 It should be also observed that in ordinary analyses of 
 the ooze there is a much larger proportion of moisture and 
 organic matter, often entered as " loss on ignition," than in 
 analyses of chalk. If, therefore, this loss and the silica be 
 taken into account, the proportion of carbonite of lime to 
 the remaining ingredients is at once made much larger. 
 
330 THE SUPPOSED PERMANENCE [CHAP. XT. 
 
 Take, for instance, the analysis of an ooze from the 
 depth of 450 fathoms, which contained 84.27 of carbonate 
 of lime, 2.60 of silica, and 4 per cent, of material lost on 
 ignition ; deducting the two latter from the total, we find 
 that 84.27 of 93.40 is equivalent to a fraction over 90 per 
 cent. ; and the analysis of this ooze is really much more 
 like Chalk than appears at first sight. Another sample of 
 ooze taken from 1,420 fathoms, and containing only 80.69 
 of carbonate of lime, really possesses a proportion of 87.70 
 to the material remaining after the abstraction of the silica 
 and loss on ignition (which amount to 7.94 per cent.). It 
 would, however, be much more satisfactory to compare the 
 ooze with analyses of those portions of the Chalk which 
 still retain a certain amount of the disseminated soluble 
 silica, and are not largely made up of the detritus of Ino- 
 ceramus shells. Such beds are known to occur in the 
 Lower Chalk, but very few analyses have yet been made of 
 them ; that, however, of a hard bed in the Lower Chalk of 
 Farnham yielded to Professor Way 2.11 per cent, of soluble 
 silica, and only 85.95 per cent, of carbonate of lime, pro- 
 portions which approximate closely to those of the same 
 minerals in the ooze from 450 fathoms. It may, therefore, 
 be concluded that the composition of the material which we 
 call chalk was originally analogous to, though not identical 
 with, that of modern oceanic ooze, and consequently that it 
 was formed under similar conditions. 
 
 5. The truth of Dr. Wallace's last argument depends 
 much on the definition of an oceanic island, and, moreover, 
 our knowledge is not yet sufficient to justify so sweeping a 
 statement. Many oceanic islands have not yet been geo- 
 logically examined, but rocks of pre-Tertiary age have 
 certainly been found on some islands which fairly come 
 under this category. Thus New Zealand and the Seychelles 
 Islands are admitted by Dr. Wallace to be exceptions to 
 his assumed rule, but he minimizes the value of New Zea- 
 
CHAP. XV.] OF CONTINENTS AND OCEANS. 331 
 
 land as an instance by doubting whether it can truly be 
 called an oceanic island. To this Mr. Crosby replies that 
 "it is difficult to see how it can be differently classified, 
 since the ocean between it and Australia is one thousand 
 miles broad and three miles deep." He proceeds, more- 
 over, to show that there are other exceptions : Spit zber gen 
 may fairly be called an oceanic island, as it is more than 
 400 miles from the nearest part of Europe, but it consists 
 largely of Palaeozoic and Mesozoic rocks. The Philippine 
 Islands again are certainly extra- continental, being sur- 
 rounded on all sides by very deep water, yet rocks of 
 Secondary age occur in them. Lastly, stratified rocks, both 
 of Palaeozoic and Mesozoic age, are stated to occur in New 
 Caledonia, which is separated by 700 miles of deep water 
 from the nearest land (Australia). Besides these there are 
 other reported occurrences of pre-Tertiary rocks on oceanic 
 islands which require confirmation. 
 
 Finally, Mr. Crosby observes, " the oceanic islands are 
 of course merely the tops of submerged mountains, and it 
 is only with the highest points of the continents that they 
 can be properly compared. Now supposing the existing 
 continents were submerged to a depth of 15,000 feet, what 
 would be the geological character of the land remaining 
 above the sea ? Palaeozoic and Mesozoic rocks would pro- 
 bably be about as scarce in it as in modern oceanic islands. 
 As a rule the loftiest mountains of the globe are composed 
 of eruptive rocks, and in many cases they are extinct or 
 even active volcanoes ; although the main mass of every 
 mountain system is formed of stratified formations." ] 
 This being so, it is only to be expected that the mountain 
 tops of a submerged continent should generally consist of 
 volcanic rocks, and even these are often covered and con- 
 cealed by the recent growth of coral-rock. 
 
 From the above considerations it is clear that the case 
 1 " Geol. Mag./' Dec. 2, vol. x. p. 251. 
 
332 THE SUPPOSED PERMANENCE [CHAP. XV. 
 
 for the permanence of oceans and continents has by no 
 means been made out, and that when the arguments which 
 have been urged in its favour are carefully examined, none 
 of them are found to be very convincing, and certainly 
 none are unanswerable. A review of the great geographical 
 transformations which the western part of Europe has 
 undergone leads to the conclusion that the present conti- 
 nent, meaning by this any compact mass of land occupying 
 the position of modern Europe, does not date back farther 
 than the beginning of Eocene time, and possibly not beyond 
 Oligocene time. The range of the Eocene Nummulitic 
 limestones proves that the whole of southern Europe, to- 
 gether with large parts of Asia Minor and of Northern 
 Africa, were at that time the site of a fairly deep sea, but 
 it is true that there was a considerable amount of land over 
 the northern part of the European region, and it may 
 therefore be argued that the continent existed, though its 
 limits were then very much circumscribed. 
 
 When, however, we go back to the Cretaceous period, it 
 must be admitted that the sea in which the Chalk was de- 
 posited had an extent (see p. 328) that fairly entitles it to 
 be called an ocean, and further, that very little land could 
 then have existed over the site of Europe, such portions of 
 northern Europe as were then land belonging in fact to a 
 more northern continent which could not by any reasonable 
 method of nomenclature be identified with modern Europe. 
 We need not, therefore, go farther afield or farther back in 
 time to find evidence for the interchange of an ocean and a 
 continent. 
 
 It may readily be admitted that the deeper parts of the 
 existent oceans are of great antiquity, and it is probably 
 not too much to say that they have never been land since 
 an early date in Mesozoic time, but this admission is very 
 different from the assertion that they date their existence 
 from the very beginning of geological history. Such geo- 
 
CHAP. XV.] OF CONTINENTS AND OCEANS. 333 
 
 logical evidence as we possess is certainly in favour of there 
 having been a large area of land on the site of the North 
 Atlantic Ocean during part of Palaeozoic time, but how far 
 this land trenched on the deeper parts of the Atlantic we 
 have no means of knowing. I agree, therefore, with 
 Professor Prestwich, who has recently expressed the 
 opinion " that it is only the deeper portions of the great 
 ocean-troughs that can claim the high antiquity which is 
 now advocated for them by many eminent American and 
 English geologists." ] 
 
 Stated in general terms, the conclusion at which we have 
 arrived may be expressed as follows : That while the posi- 
 tion of our modern oceans and continents has not been 
 permanent from the earliest geological times, they are 
 nevertheless of very ancient date ; and we may infer that 
 the replacement of an ocean by a continent, or vice versa, is 
 a process which has not taken place many times in the 
 history of any one portion of the earth's surface. 
 
 To my mind, indeed, the study of the geological evidence 
 suggests an inference which is different from either of the 
 theories which have been discussed. It has already been 
 observed that the absence of anything like deep oceanic 
 deposits among the Palaeozoic rocks may be taken as in- 
 dicative of a great difference in the general relations and 
 proportional areas of land and sea, the probability being 
 that there were neither oceans nor continents like those 
 which now exist, but an irregular distribution of compara- 
 tively shallow seas among land-tracts of moderate eleva- 
 tion. In Neozoic times we find proof of the existence of 
 oceans, though these do not seem to have been so deep as 
 those of the present day ; that there were also large tracts 
 of continental land is proved by the traces of large rivers 
 and large inland lakes, but so far as we know these land- 
 tracts did not form the nuclei of the modern continents of 
 1 Prestwich 's " Geology," vol. ii. p. 547. 
 
334 THE SUPPOSED PERMANENCE [CHAP. XV. 
 
 Europe, Asia, and Africa, or bear any other definite rela- 
 tion to these continents. 
 
 If these inferences are correct, may we not deduce the 
 still more comprehensive conclusion, that the deep ocean- 
 basins and lofty mountain ranges of the modern world 
 have been formed by a long process of geographical evolu- 
 tion, which has proceeded pari passu with the development 
 and differentiation of the animals and plants which in- 
 habit them, the tendency of all recent geographical 
 changes having been to deepen the ocean-basins and to 
 raise the mountain-peaks to higher and higher elevations. 
 
 This theory has at any rate the advantage of being 
 based on definite facts, of reconciling many points of 
 difficulty, of avoiding extremes, and of being in accordance 
 with the general principle of Evolution. I state it in order 
 that it may receive consideration from capable critics, and 
 time will prove whether or not it is a tenable view. That 
 it avoids the two extremes of complete permanence and 
 frequent interchange is by no means its least recom- 
 mendation, for the history of scientific controversies shows 
 that antagonistic views have often been reconciled by an 
 hypothesis which concedes something to both sides, for 
 scientific men are not exempt from the common failing of 
 veering too rapidly from one extreme to another, when in 
 so many cases the truth lies midway between the extreme 
 views. The advice which Horace gave to his friend Licinius, 
 and which Ovid so tersely expresses by the words, 
 
 " medio tutissimus ibis," 
 
 is equally applicable to the ways of science and philosophy. 
 Thus I feel convinced that the truth is neither with those 
 who assert the complete permanence of oceans and conti- 
 nents, nor with those who teach the frequent conversion of 
 one into the other. Similarly, that the existence of the 
 calcareous ooze in modern oceans should be regarded as 
 
CHAP. XV.] OF CONTINENTS AND OCEANS. 335 
 
 proving the present to be only a continuation of the Cre- 
 taceous period, I hold to be as untrue as the opinion that 
 the Chalk is not the product of a Cretaceous ocean. So 
 also with the arguments of those who urge and those who 
 oppose the doctrine of Uniformity in the rate of geologic 
 change ; the Unif ormitarian may push his advocacy to 
 such an extreme that he departs almost as far from the 
 truth in one direction as the Convulsionist does in another. 
 Avoiding these extremes, we may believe in the long- 
 continued existence of continents and oceans, and yet 
 admit that the Chalk is a genuine oceanic deposit ; we 
 may adopt the doctrine of Uniformity as our guiding 
 principle in the interpretation of the past, and yet believe 
 in the theory of Evolution. 
 
INDEX. 
 
 A. 
 
 ABERDEEN, glacial beds of, 
 263. 
 
 Anglesey, rocks of, 30, 57, 76. 
 Antrim, lavas of, 209, 316. 
 Antwerp Crag, 239. 
 Aptien, 164. 
 Arbroath flags, 51. 
 Archaean rocks, 13. 
 Arctic-plant bed, 286. 
 Arctic regions, rocks of, 38, 86. 
 Ardennes, rocks of, 63. 
 Arenig series, 28. 
 Artois, axis of, 230. 
 Atlantic, Palaeozoic land in, 24, 
 
 37, 45, 86. 
 
 Atlantic Ocean, formation of, 107. 
 Austen. See Godwin- Austen. 
 
 B. 
 
 Bagshot Beds, Lower, 201, 204, 
 
 225. 
 
 - Middle, 206, 225. 
 
 Upper, 206. 
 
 Bala series, 28. 
 
 Bangor Beds, 17. 
 
 Barrois, Dr. C., 88, 178, 198, 230. 
 
 Barton Clay, 207. 
 
 Beccles, boring at, 256. 
 
 Belgium, Eocene of, 229. 
 
 Crag of, 239, 244. 
 
 Bell, Mr. A., 252. 
 Bembridge Beds, 211. 
 Blackheath Beds, 201, 218. 
 Blake, Professor J. F., 142. 
 Boom, argile de, 213, 233. 
 Bonney, Professor T. G., 21, 119, 
 
 120, 128, 129. 
 Borrowdale series, 31. 
 Boulder-clays, 262, 265, 274, 278, 
 
 287. 
 
 Bournemouth Beds, 204, 206, 226. 
 Box-stones, 236, 241. 
 Bracklesham Beds, 206. 
 
 fossils, 228. 
 Breccias, Jurassic, 144. 
 
 near Nice, 128. 
 
 Permian, 105, 111. 
 
 Triassic, 117. 
 
 Brighton, depth of chalk near, 
 
 199. 
 ! Bristol coalfield, 93. 
 
 Brittany, rocks of, 48, 63, 88. 
 
 Bruxellien, 229. 
 
 Bunter Beds, 116. 
 
 formation of, 129. 
 
 Burford, boring at, 116, 138. 
 i Burnley coalfield, 93. 
 
 C. 
 
 Cadell, Mr. H. M., 84. 
 
 Caithness flags, 61. 
 
338 
 
 INDEX. 
 
 Calcaire grossier, 208. 
 Caledonia, Old Red Sandstone 
 
 lake of, 61, 64. 
 Callaway, Dr. C., 13, 15, 19, 25, 
 
 30, 33. 
 
 Cambrian period, 16. 
 Cambridge Greenland, 173. 
 Carboniferous Limestone, 69, 71, 
 
 90. 
 
 period, 69. 
 
 geography, 83, 305. 
 
 slate, 54. 
 
 Carse clays, 264, 302. 
 
 Caspian Sea, 112, 146. 
 
 Chalk, 164, 174. 
 
 composition of, 174, 176, 
 
 329. 
 
 a deep-sea deposit, 328. 
 
 range of, 328. 
 
 thickness of, in borings, 198. 
 
 Lower, 175. 
 
 Middle, 176. 
 
 Upper, 178. 
 
 Marl, 173, 174. 
 
 Rock, 176. 
 
 Chalky Boulder-clay, 266, 283. 
 Chatham, boring at, 198. 
 Chartham, boring at, 198. 
 Cheshunt, boring at, 198. 
 Cheviot, Lake, 60, 65. 
 Chillesford Beds, 243, 244. 
 Chloritic Marl, 173. 
 Clays, 5. 
 
 Coal-measures, 69, 70, 90, 92, 99. 
 Codrington, Mr., 270. 
 Conglomerates, 3. 
 
 Cambrian, 16. 
 
 Carboniferous, 73, 75, 76, 80. 
 
 Cretaceous, 168. 
 
 Dyassic, 105. 
 
 - Eocene, 201, 221. 
 Liassic, 136. 
 
 Conglomerates, Ordovician, 27, 
 
 30, 33. 
 
 Old Red, 53, 57, 58, 66. 
 
 Silurian, 40, 42, 43. 
 
 Triassic, 117, 119, 120, 122. 
 
 Continents, permanence of, 324. 
 Contorted Drift, 283. 
 Coralline Crag, 239, 251. 
 Coral Rag, 142. 
 
 Cornet and Briart, Messrs., 126. 
 Cornwall, rocks of, 48, 55. 
 Cornstone series, 50. 
 Cotteswolds, map of, 269. 
 Crag, Newer, 236, 240, 242. 
 
 Older, 236, 240. 
 
 Cretaceous period, 168. 
 
 geography, 178, 312. 
 
 Croll, Dr., 280. 
 
 Cromer, glacial deposits of, 266, 
 
 282. 
 
 Crosby, Mr. W. O., 325, 331. 
 Crossness, boring at, 123. 
 Culm-measures, 69. 
 
 I). 
 
 Dana, Professor, 324, 325. 
 Daubree, Professor, 4. 
 Dawkins, Professor Boyd, 258, 
 
 294, 296, 297, 300. 
 Deep-water beds, 6, 327. 
 Denbigh Grits, 46. 
 Devonian system, 49, 55. 
 
 geography, 63. 
 
 Diestien Sands, 239, 251. 
 Dogger Bank, 293. 
 Dolfuss, M., 213. 
 Dolomite, formation of, 112. 
 Dover, Straits of, 292, 321. 
 Drew, Mr. F., 60. 
 Drums, 281. 
 
INDEX. 
 
 339 
 
 Durness, rocks of, 33. 
 Dutton, Captain C. E., 215. 
 Dyassic period, 102. 
 geography, 106. 
 
 E. 
 
 East Horsley, boring at, 198. 
 
 Eigg, Scuir of, 210. 
 
 English Channel, valley of the, 
 
 296. 
 Eocene period, 196. 
 
 geography, 213, 314. 
 
 volcanoes, 216, 316. 
 
 Erratics, dispersal of, 285. 
 Evolution, geographical, 2, 304, 
 
 334. 
 
 F. 
 
 Fanad, Lake, 63. 
 Faroe Islands, 216, 252, 258, 301. 
 Fitton, Dr., 166. 
 Flints in Scotland, 194. 
 Fontainebleau, Gres de, 212. 
 Forbes, Professor E., 145, 148, 
 298. 
 
 Professor J. D., 281. 
 
 Forest bed, 245, 259. 
 Forests, submerged, 273, 299. 
 France, Cretaceous of, 163, 164. 
 
 Devonian of, 56. 
 
 Eocene of, 205, 227. 
 
 Miocene of, 235. 
 
 Ordovician of, 48. 
 
 Trias of, 123. 
 
 G. 
 
 Gardner, Mr. J. S., 200, 204, 205, 
 209, 220, 223, 225, 227, 233, 
 325. 
 
 Gault, 170, 187. 
 
 Geikie, Dr. A., 14, 52, 59, 60, 61, 
 
 182, 194, 210, 279, 324, 327. 
 Geikie, Professor J., 262, 264, 
 
 271, 272, 274, 277, 281, 285, 
 
 292, 297, 300. 
 Geographical evolution, 2, 304, 
 
 334. 
 
 Girvan, rocks of, 32, 42. 
 Glacial deposits, 261, 262, 265, 
 
 273. 
 
 Glengariff Grits, 54. 
 Godwin- Austen, Mr., 27, 157, 
 
 258, 259. 
 
 Goodchild, Mr. J. G., 81, 82, 281. 
 Gosselet, Professor J., 63, 162, 
 
 222, 229, 230. 
 Gravels, Glacial, 268, 289. 
 
 Plateaux, 268, 291. 
 
 River, 264, 271, 291. 
 
 Green, Professor A. H., 86, 89, 
 
 92, 95, 100, 125. 
 Greenland, connection of Britain 
 
 with, 215, 252, 287, 314. 
 Greensand, Lower, 166. 
 
 Upper, 170. 
 
 Upper, geography of, 188. 
 
 Greywethers, 204. 
 Guillier, Mons. A., 173. 
 Gunn, Mr. J., 259. 
 
 H. 
 
 Hantonian period, 196. 
 
 geography, 213. 
 
 Hardman, Mr., 274. 
 Harlech Beds, 17. 
 Harris, Mr. G. F., 224. 
 Harrison, Mr. W. J., 119, 120. 
 Harwich, boring at, 198. 
 Hastings Sands, 164. 
 
340 
 
 INDEX. 
 
 Headon Beds, 210, 232. 
 Hebert, Professor E., 162, 230. 
 Hempstead Beds, 212, 233. 
 Hessle Clay, 268, 283. 
 Hicks, Dr. H., 19, 23, 24. 
 Highlands, land in Carboniferous 
 
 time, 84. 
 
 scenery of the, 52. 
 
 Hill, Mr. W., 171, 172, 174, 176. 
 Hordwell Sands, 207. 
 Horsley, East, boring at, 198. 
 Hudleston, Mr. W. H., 156. 
 Hull, Professor E., 24, 54, 59, 62, 
 
 86, 107, 108, 110, 151, 157, 270, 
 
 274, 325. 
 
 Humber valley, date of, 255. 
 Hunstanton limestone, 171. 
 
 I. 
 
 Iceland, Britain connected with, 
 253, 260. 
 
 Icenian period, 235, 261. 
 
 Imperfection of the geological re- 
 cord, 11. 
 
 Inferior Oolite, 138. 
 
 Ingleborough, 82. 
 
 Interglacial deposits, 275, 279. 
 
 Ireland, Cambrians of, 20. 
 
 Carboniferous of, 72. 
 
 Chalk of, 176, 178, 179. 
 
 Glacial beds of, 273. 
 
 Greensand of, 173. 
 
 isolation of, 298. 
 
 Old Red Sandstone of, 54, 58. 
 
 Ordovician of, 35. 
 
 Permian of, 105. 
 
 Silurian of, 44. 
 
 Irving, Rev. A., 206, 207, 222, 
 225. 
 
 Isle of Man, 75, 76. 
 
 J. 
 
 Jamieson, Mr., 258, 262, 263, 281. 
 Judd, Professor J. W., 21, 137, 
 
 141, 144, 216, 316. 
 Jukes, Professor J. B., 73, 74, 
 
 79, 273. 
 
 Jurassic period, 135. 
 geography, 149, 311. 
 
 K. 
 
 Kellaways Beds, 155. 
 Kendall, Mr. J. D., 252. 
 Kentish Town, boring at, 123. 
 Keuper Beds, 121. 
 
 Lake, 131. 
 
 Kiltorcan Beds, 58, 67. 
 Kimeridge Clay, 142, 158. 
 Kinahan, Mr. G. H., 72, 275, 276. 
 
 Lake District, 30, 80, 81, 104. 
 Lancashire coalfield, 93. 
 Lankester, Professor Ray, 236. 
 Lapparent, Mons. de, 48, 63, 150, 
 
 195. 
 
 Lapworth, Professor, 32, 33, 43. 
 Lenham Sands, 237, 238. 
 Lias, 133. 
 
 Liassic Sea, 148, 311. 
 Limestones, 5, 6. ? 
 Lincolnshire limestone, 139. 
 Lingula Flags, 17, 18, 20. 
 Linnarsson, Professor, 23. 
 Llanberis grits and slates, 17, 20. 
 Llandeilo Flags, 23. 
 Llandovery Beds, 40. 
 London Clay, 201, 222, 223. 
 
INDEX. 
 
 341 
 
 London Sands, 205. 
 Longmynd, rocks of the, 17, 18, 
 19. 
 
 an island, 47. 
 
 Loughton, boring at, 198. 
 Lower Greensand, 166. 
 Lyell, SirCh., 128,324,328. 
 
 M. 
 
 Mackintosh, Mr. D., 285, 289. 
 
 Marr, Mr. J. E., 14, 38. 
 
 Mell Fell conglomerate, 80. 
 
 Menevian Beds, 17. 
 
 Meux's Brewery, boring at, 140. 
 
 Meyer, Mr. C. J. A., 145, 160, 
 
 166, 179. 
 
 Middlesborough, borings at, 103. 
 Midford Sands, 152. 
 Miller, Hugh, sen., 52. 
 
 - Hugh, jun., 302. 
 Millstone Grit, 69, 70, 90, 92, 93, 
 
 95. 
 Miocene epoch, 234. 
 
 geography, 246. 
 
 Moel Tryfaen, 265. 
 Moffat Beds, 33, 42. 
 Morris, Professor J., 169. 
 Morton, Mr. G. H., 77. 
 Mull, lavas of, 209. 
 Murchison, Sir R., 38, 61. 
 Murray, Mr. J., 294. 
 
 N. 
 
 Neocomian group, 163. 
 
 Neolithic man, 300. 
 
 Neozoic rocks, position of, 112. 
 
 oceans, depth of, 333. 
 
 Newark, boring near, 103. 
 Nice, deposits near, 128. 
 Normandy, rocks of, 63. 
 
 Northampton, borings near, 79, 
 
 122. 
 North Sea, origin of, 257, 317. 
 
 shallowing of, 320. 
 
 Norwich Crag, 243, 255. 
 Nummulitic limestones, 227, 332. 
 
 O. 
 
 Oceans, permanence of, 324. 
 
 evolution of, 334. 
 
 Oceanic deposits, 326, 328. 
 
 rarity of among ancient 
 
 rocks, 326, 327. 
 Oceanic islands, 330. 
 Old Red Sandstone, Lower, 50. 
 
 - Upper, 56, 57. 
 Oldhaven Beds, 201. 
 Oligocene deposits, 210. 
 
 geography, 231, 315. 
 
 Oolite, Great, 138, 154. 
 
 Inferior, 138, 152. 
 
 Ooze, oceanic, 326, 328. 
 Orcadie, Lake, 61, 64. 
 Ordovician period, 27. 
 
 geography, 36. 
 
 Ortlieb, Mons., 229. 
 Orton, boring at, 79. 
 Osborne Beds, 211. 
 Overlap, 10. 
 
 Owthorpe, boring at, 103. 
 Oxford Clay, 141. 
 geography of, 155. 
 
 P. 
 
 Palaeolithic gravels, 271. 
 
 man, 292. 
 
 Palaeozoic geographies, uncer- 
 tainty of, 38, 305. 
 seas, depth of, 333. 
 
342 
 
 INDEX. 
 
 Paris, Eocenes of, 205, 227. 
 Peach, Mr. B. N., 15, 21, 34, 37, 
 
 67. 
 Pebble Beds, 3. 
 
 of Trias, 119, 129. 
 
 of Eocene, 201, 218. 
 
 Pennine chain, 81, 106, 108, 309. 
 Permian system, 102. 
 Permanence of continents, &c., 
 
 324. 
 
 Phillips, Mr. J. A., 4, 119. 
 Plateaux gravels, 268. 
 Pleistocene epoch, 261. 
 
 geography, 291, 320. 
 Pliocene epoch, 236. 
 
 geography, 248, 318. 
 
 Portraine, rocks of, 35. 
 Portland Beds, 142. 
 
 epoch, geography of, 159, 312. 
 
 Post-glacial deposits, 261, 264. 
 Pourtales, Mons., 328. 
 Prestwich, Professor, 195, 196, 204, 
 
 207, 218, 220, 221, 224, 227, 
 
 236, 243, 255, 259, 323, 333. 
 Purbeck Beds, 144. 
 geography, 160. 
 
 R. 
 
 Raised beaches, 268, 275, 302. 
 Ramsay, Sir A., 26, 46, 59, 112, 
 
 127, 128, 148, 265. 
 Reade, Mr. T. M., 265, 268, 274. 
 Reading Beds, 200, 218. 
 Red Chalk, 171. 
 Red Crag, 242, 255. 
 Reid, Mr. Clement, 212, 237, 242, 
 
 245, 248, 250, 259, 266, 268, 286. 
 Rhsetic Beds, 133, 146. 
 Richmond, boring at, 123, 140, 
 
 169, 198. 
 
 Ricketts, Dr. C., 215. 
 River-gravels, 264, 271, 291, 293. 
 Rupelien, 213. 
 
 S. 
 
 Sables de Cuise, 205. 
 
 Saffron Walden, boring at, 169. 
 
 Sandstones, 3. 
 
 Scandinavia, Cambrian of, 22, 23, 
 
 24. 
 
 Carboniferous of, 85. 
 
 Scotland, Cambrian of, 21. 
 
 Carboniferous of, 70, 82. 
 
 Chalk of, 177, 178. 
 
 Eocene of, 209, 216. 
 
 Glacial beds of, 262. 
 
 Lias of, 136. 
 
 Oolites of, 140. 
 
 Ordovician of, 32. 
 
 Old Red of, 51, 58. 
 
 Pleistocene of, 262. 
 
 Silurian of, 42. 
 
 Trias of, 124. 
 
 Sedgwick, Professor, 27. 
 Shallow-water deposits, 3. 
 Shanklin Sands, 166. 
 Sheppey, London clay of, 224. 
 Shotover Beds, 168. 
 Shropshire, section through part 
 
 of, 29, 
 
 Silica, soluble, 329. 
 Silurian period, 40. 
 
 geography, 45. 
 
 Skertchly, Mr. S. B. J., 271. 
 
 Skiddaw slates, 31. 
 
 Sorby, Dr. H. G., 119, 171. 
 
 Southwold, boring at, 256. 
 
 Spitzbergen, rocks of, 88, 149. 
 
 St. Erth Beds, 242, 250. 
 
 St. George's Channel, formation 
 
 of, 292, 317. 
 
INDEX. 
 
 343 
 
 Stonesfield Slate, 31. 
 Strahan, Mr. A., 265, 268. 
 Streatham, boring at, 198. 
 Submerged forests, 273, 276. 
 Subsidence, recent, 321. 
 Symonds, Rev. W. S., 50, 57. 
 
 T. 
 
 TeaU, Mr. J. J. H., 108. 
 Thames Valley, date of, 247, 
 
 255. 
 
 Thanet Beds, 199, 217. 
 Thinning out of beds, 7. 
 Till, 262. 
 Tongrien, 213. 
 Torridon Sandstone, 21. 
 Totternhoe Stone, 175. 
 Tremadoc Slates, 17, 20. 
 Trent Valley, date of, 256. 
 Triassic period, 114. 
 geography, 124, 307. 
 
 U. 
 
 Unconformities, meaning of, 8. 
 Uniformity, doctrine of, 334. 
 Upheaval of the Weald, 218. 
 
 of Scotland, recent, 322. 
 
 Urgonien, 163. 
 
 Ussher, Mr. \V. A. E., 117, 271. 
 
 Utrecht, boring at, 239, 320. 
 
 V. 
 
 Valleys, Miocene, 247. 
 
 Pliocene, 254. 
 
 Post-glacial, 290. 
 
 Pre-glacial, 286. 
 
 Vandenbroeck, Mons. E., 239. 
 Vectian group, 166. 
 
 Vectian geography, 186, 313. 
 
 sea, 185, 313. 
 
 Volcanic group of Lake District, 
 
 31. 
 Volcanoes of the Eocene period, 
 
 216. 
 
 W. 
 
 Wales, North, 17, 28, 30, 41, 46, 
 
 76, 78, 265. 
 
 South, 19, 28, 57, 72, 136. 
 
 Wallace, Dr. A. R., 253, 298, 
 
 301, 324, 325, 328, 330. 
 Walpen Sands, 166. 
 Ward, Rev. J. C., 31, 42, 79. 
 Ware, boring at, 41, 116. 
 Wash, formation of the, 255. 
 Watson, Rev. B., 280. 
 Way, Professor, 330. 
 Weald, upheaval of the, 219. 
 condition of, in Miocene time, 
 
 249. 
 Wealden Beds, 164. 
 
 - Lake, 179. 
 Wenlock Beds, 41. 
 Weybourn Crag, 244. 
 Whitaker, Mr. W., 199, 200,201, 
 
 202, 204, 218, 221. 
 Wilson, Mr. E., 108, 112. 
 Woodward, Mr. H. B., 118, 136, 
 
 255, 257, 261, 266, 294. 
 Woolwich Beds, 199. 
 
 Y. 
 
 Yoredale Beds, 69, 81. 
 Yorkshire, Carboniferous of, 89. 
 
 Cretaceous of, 169, 171. 
 
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