Thomas 
 Westmorland Slates
 
 THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 LOS ANGELES 
 
 The RALPH B 
 
 LO-
 
 Hr 
 
 Westmorland Slates 
 
 (Ufieir (s^eofogtj, diftemi^trij, anel 
 
 A PAPER READ BEFORE 
 
 MANCHESTER SOCIETY OF ARCHITECTS 
 7TH JANUARY 1896 
 
 J. J. THOMAS, M.I.M.E. (Kendal) 
 
 Member of the In.ititutf of Mi/iini/ anil Mechanical Engineers, Newcastle 
 
 Member of the Mininv Assnc.intion and Institute of Cornwall; 
 
 Manager of Jas. Stephensrm <t Co.'.v Tilhertfiinnte 
 
 Green Nii/e Quarries 
 
 REPRINTED FROM THE 
 JOURNAL OF THE ROYAL INSTITUTE OF BRITISH ARCHITECTS 
 
 VOL. III. THIRD SERIES, NO. 6 
 
 SPOTTISWOODE & CO., NEW-STREET SQUARE, LONDON 
 1896
 
 WESTMORLAND SLATES 
 
 THEIR GEOLOGY, CHEMISTRY, AND 
 ARCHITECTURAL VALUE 
 
 A PAPER READ BEFORE 
 
 THE MANCHESTER SOCIETY OF ARCHITECTS 
 7TH JANUARY 1896 
 
 BY 
 
 J. J. THOMAS, M.I.M.E. (KBNDAL) 
 
 Afeniber of the Institute of Mining and Mt-i'hfinical Engineers, Nric 
 Member of the Miiiintj Ats<icititin ami Institute of Cornwall; 
 Manaijer of Jas. Stevenson <0 C'o.'s Tilberthwaite 
 Green Klate Quarries 
 
 REPRINTED FKOM THE 
 
 JOURNAL OF THE ROYAL INSTITUTE OF BRITISH ARCHITECTS 
 VOL. III. THIRD SERIES, NO. ti 
 
 SrOTTISWOODE & CO., XKVV-STREET SQUARE, LONDON 
 1896
 
 Oology 
 Library 
 
 TN 
 
 WESTMOBLAND SLATES: 
 
 THEIR GEOLOGY, CHEMISTRY, AND 
 ARCHITECTURAL VALUE. 
 
 BY J. J. THOMAS, KENDAL. 
 Read before the Manchester Society of Architects, 7th January 1896. 
 
 So far as I am aware, it is seldom that slates and slate- 
 quarrying form the subject of a Paper to be read before an 
 Architectural Society, and I wish to say at the outset that 
 the opportunity now afforded of placing on the records of 
 this important Society some account imperfect though 
 it be of Westmorland slates is one which I highly 
 appreciate. 
 
 It will be generally admitted, I believe, that slates de- 
 serve to be classed among the most important materials 
 with which the architect, during the course of his profes- 
 sional career, has to deal ; but it is doubtful whether the 
 same scientific study has been made of them as of many 
 other articles used in architectural work. It may be in- 
 teresting at this point to give some idea of the magnitude 
 of the industry which we have under consideration, and 
 the quantity of slates produced in this country. I find 
 from official statistics that about 15,000 men are employed 
 in the slate quarries of Great Britain and Ireland ; and that 
 they produced, in 1894, 461,673 tons of slates, amounting 
 in value to 1,171,366 ; out of this total 940,553 worth 
 were used in this country, the remainder being exported to 
 various foreign countries, a list of which, with the quantities 
 sent to each and their values, I append to this Paper. It 
 is also interesting to note that the slate trade comes fourth 
 on the list of those industries tabulated in the mineral 
 statistics of Great Britain and Ireland. Coal comes first. 
 
 1051'
 
 the value in 1894 being 62,730,179 ; stone, 7,095,716 ; 
 iron ore, 3,190,647 ; slates, 1,171,366. 
 
 From the foregoing figures it will be seen that the slate 
 industry in this country is one of very considerable magni- 
 tude, and represents in money value a large annual turn- 
 over. 
 
 In order to make the Paper easy to follow and as in- 
 telligible as possible, I propose to deal with the subject 
 under three main headings : 
 
 1. The Geological Position and Extent of the Slate - 
 producing Area of the Lake District. 
 
 2. The Chemical Composition of Slates, and the Action 
 upon them of Impure Atmospheres and varying Degrees 
 of Temperature. 
 
 3. General Description of Westmorland Slate-Quarrying, 
 the Method of preparing the Slates, Cleavage, Architectural 
 Value. 
 
 The Geological Position and Extent of the Slate-Pro- 
 ducing Area of tlie Lake District. The Lake District 
 proper is composed of Silurian strata, both the lower and 
 upper divisions of the formation being represented, and 
 they may be divided into five groups, which I give in order 
 of deposition, viz. : 
 
 Skiddaw Slates, 7,000 feet . . . . ) T 
 
 Green Slate and Porphyry Series, 7 to 10,000 feet Vo-T' 6 
 Collision Limestone, 300 feet . . . . J bli 
 Coniston Flags and Grits, 7,000 feet . ) TT c-i 
 Ludlow Rocks, 5,200 feet . . . j U PP er Silurian. 
 
 From the above table it will be seen that the Skiddaw 
 Slates, which comprise a group of rocks of enormous 
 thickness, and cover an area of about 200 square miles, 
 form the base of the Lower Silurian series of the Lake 
 District, and have their equivalent in the Arenig Slates or 
 Lower Llandeilo Flags of North and South Wales. 
 
 The group mainly consists of dark slates or slaty mud- 
 stones, with occasional beds of harder material of a flaggy 
 nature, but almost devoid of cleavage. Some geologists 
 describe the Skiddaw Slates as of little industrial import- 
 ance : so far as slates are concerned, this may be correct, 
 as, with the exception of Bowscale Fell and Embleton 
 Valley Slate Quarries, both of which, I believe, are now 
 idle, no roofing slates are obtained from this group. But 
 several important, and at one time lucrative, mineral de- 
 posits were worked in this formation, among which may 
 be mentioned the famous Goldscope Mine, which produced 
 in former years both gold and copper, the latter, it is said, 
 in large quantities. A number of other mines produced 
 lead, copper, iron, and cobalt. It may also be stated that
 
 good Hags have been quarried at Crummock, and near 
 Shap slate pencils were once largely produced. 
 
 Lying conformably on the Skiddaw Slates are the Green 
 Slate and Porphyry series, also of Lower Silurian age. their 
 equivalent in the Silurian Rocks of North and South Wales 
 being part of the Bala Beds, the whole of Llandeilo, and 
 probably part of the Arenig formation. . 
 
 It need hardly be mentioned that this group of rocks is 
 one presenting many points of considerable interest, and 
 has for years attracted the attention of some of our leading 
 men of science, several of whom have placed on record, at 
 considerable length, the result of their investigations; and, 
 although it would be extremely interesting to follow some 
 of these geological pioneers in the study of these rocks, I 
 shall only briefly notify their chief geological features, and 
 proceed more especially to deal with them as slate-produc- 
 ing rocks, as it is from this formation that all the West- 
 morland green roofing slates of commerce are obtained. 
 
 The group is one of great superficial extent, extends 
 twenty-five miles in an E.N.E. and W.S.W. direction, and 
 averages about thirteen miles in a N.W.W. and S.S.E. 
 direction ; covers an area of about 325 square miles, and 
 attains a thickness of about 10,000 feet. It is composed 
 of a vast accumulation of bedded felspathio ashes and 
 breccia, with alternate beds of porphyries of considerable 
 thickness. The whole group, which is entirely devoid of 
 fossils, except a small band near the top, is the result of 
 a series of volcanic actions, estimated to have spread over 
 a period of about one and a half million years. The chief 
 centres of this volcanic activity are supposed to have been 
 Ambleside and Keswick, in addition to which there were 
 several other smaller centres of irruption in various parts 
 of the district. 
 
 The volcanic activity which commenced at the close of 
 the Skiddaw Slate period is not supposed to have been 
 marked in its earlier stages by any general upheaval of 
 rocks. In all probability the earlier volcanic outbursts 
 were submarine, as the rocks at Eycott Hill, near Black 
 Coombe, and also in an exposure near Shap, seem to point 
 to the conclusion that the lower deposits, although in all 
 probability thrown high above the water, fell back and were 
 interstratified with deposits of mud and sand. Later in the 
 period, however, it seems clear that the volcanic action was 
 accompanied by a gradual upheaval of the old ocean bed. 
 
 Turning now to the series, and examining it from a 
 quarrying and slate-producing point of view, I think it 
 may be safely stated that it presents more difficulties and 
 complications than any other slate-producing formation
 
 on the geological chart. Out of the whole 325 square miles 
 which this group covers, there are only about twelve or 
 fourteen beds from which slates are obtained. Ten or 
 twelve of these are situate near the top of the series in the 
 Coniston district, and the remainder at the base of the 
 series in the neighbourhood of Keswick. The whole area 
 between these two points is practically barren of any rock 
 sufficiently well cleaved to produce roofing slates. 
 
 It may be pointed out here that the fine ash beds from 
 which the slates are obtained are in each case in close 
 proximity to where the main centres of eruptions are sup- 
 posed to have been located, and this may point to a period 
 of less violent volcanic activity than when the porphyries 
 and breccias were emitted. 
 
 Accompanying the fine ash beds are almost invariably 
 found beds of breccia, also cleaved, but generally too rough 
 and coarse in the grain to make marketable roofing slates. 
 One of the principal difficulties to contend with in this 
 series is the uncertainty of the continuity of the bed of slate, 
 from the fact that there is a marked difference between a 
 volcanic deposit and a sedimentary formation. The former 
 is not only subject to considerable variation in the charac- 
 ter as well as in the degree of fineness of its deposit, but 
 also in its extent ; while, on the other hand, sedimentary 
 formations, such as occur in North Wales, have been 
 formed under deep sea, and during a period of comparative 
 calmness. You will therefore readily understand why a 
 sedimentary bed is much more regular than a fine ash bed 
 emitted from the crater of a volcano. 
 
 Coniston Limestone. The Green Slate and Porphyry 
 series is overlaid by the Coniston Limestone, a narrow 
 band averaging about 300 feet in thickness, and extending 
 from Millom to Wasdale Crag, near Shap. This is con- 
 sidered to be the equivalent of the Bala Limestone of 
 North Wales, and is the topmost bed of the lower Silurian 
 Rocks of the Lake district. It consists of hard and com- 
 pact limestone of a dark blue colour, and is largely inter- 
 mixed with cleaved slates. It is of little or no commercial 
 value. 
 
 The Limestone is succeeded by the Stockdale SJiales, a 
 narrow group of Graptolitic mudstones, with bands of dark 
 and purple shales, forming the base of the Upper Silurian 
 of the district. On Torver and Broughton Moors several 
 attempts have been made at quarrying these shales for 
 slates and flags, but hitherto the discoveries have not been 
 of an encouraging character. 
 
 Lying on the Stockdale Shales are the Coniston Flags 
 and Grits, which are precisely the same as the Denbigh-
 
 UUlale 
 
 OaMbppk 
 
 - Matterdale
 
 10 
 
 shire Grits and Flags overlying the Tarranon Shale in 
 North Wales. The lower bed the flags attains a thick- 
 ness of about 2,800 feet, while the grits measure 4,000 feet 
 in thickness. The flags consist of dark blue sandy mud- 
 stones, which when cleaved are largely quarried for slates 
 and flags, the principal quarries in this series being on 
 Torver and Kirkby Moors. The grits are composed of 
 harder material, principally gritty sandstones with inter- 
 stratified beds of slates and flags. These bring us to the 
 Ludlow Rocks, an extensive group of fossiliferous rocks 
 extending from Kendal to the Lune Valley, and, as 
 will be seen from the section, are of the same geological 
 age as the formation bearing the same name in North 
 Wales. 
 
 The above brief outline of the geology of the slate forma- 
 tions brings us to the next heading viz. : 
 
 The Chemical Composition of Slates, and the Action 
 upon them of Impure Atmospheres and varying Degrees of 
 Temperature. However interesting and valuable may be 
 the inquiry into the geological history and relative age of 
 the various slate-producing rocks, and the manner in which 
 they have been formed, it is possible that from a utilitarian 
 point of view the chemical analysis of the slates, and the 
 effect varying degrees of temperature, &c., have upon them, 
 is equally, if not more, important to us, 
 
 There is probably no article of domestic use with which 
 we are more familiar and have more prominently brought 
 before us than a slate ; even from our earliest schooldays 
 we were brought face to face with this useful article of 
 commerce. It is, however, doubtful whether many, even 
 of those who most frequently use them, have thought it 
 necessary and of sufficient importance to inquire into the 
 characteristics and relative values of the different kinds of 
 slates. 
 
 It is a remarkable fact that although, as will be readily 
 admitted, there is a great difference in the " wearing" 
 quality of the various descriptions of slates, the variation 
 in the chemical compositions is exceedingly slight. I will 
 give the analyses of some of the principal varieties of 
 roofing slates. 
 
 1. Analysis of ordinary blue Welsh roofing slate, 
 Cambrian formation ; by Professsor Hull. 
 
 Silica 60-50 
 
 Alumina ....... 19'70 
 
 Iron (protoxide) 7 '83 
 
 Lime ri2
 
 Magnesia ...,,.. 2'20 
 
 Potash 8-18 
 
 Soda 2-20 
 
 Water 3'30 
 
 2. Analysis of a dark-blue slate from Llangynog, 
 North Wales ; by D. H. Richards. 
 
 Silurian Rock. Slate dried at 100 C. 
 Loss on ignition .... 
 
 Silica 
 
 Alumina ...... 
 
 Protoxide of Iron .... 
 
 Sesquioxide of Iron .... 
 
 Not determined (alkaliesj 
 
 . Analysis of the material of the green bands in tlie 
 bluish-purple slates at Llanberis ; made by the E< yal 
 School of Mines. Cambrian formation. 
 
 Silica r>(>-|."> 
 
 Titanic Acid 0'63 
 
 Alumina l:\~W 
 
 Protoxide of Iron ..... 1'71 
 
 Peroxide of Iron 1'41 
 
 Protosesquioxide of Manganese . . - 91 
 
 Lime 2-8(5 
 
 Magnesia 6'28 
 
 Potash 0-05 
 
 Soda . 0-90 
 
 Carbonic Acid I'oO 
 
 Combined Water 8'90 
 
 Hygroscopic Water <>'U; 
 
 99-91 
 
 4. Analysis of the purple slates of Nantlle. Kirwan's 
 Mineralogy. Cambrian formation. 
 
 Silica 48 
 
 Argillaceous Matter 2(! 
 
 Magnesia 8 
 
 Lime 4 
 
 Iron . . 14
 
 12 
 
 5. Analysis of a green Westmorland slate ; by George 
 Vogt. 
 
 Silica 50'88 
 
 Alumina 14'12 
 
 Iron Oxide (Ferrous) .... 9'96 
 
 Lime 8'72 
 
 Magnesia 8'67 
 
 Carbon Dioxide 6'47 
 
 Potash -88 
 
 99-70 
 
 It will be seen from the foregoing analyses that slates 
 are chiefly made up of silica and alumina, from which we 
 may reasonably infer that they were once ordinary clay. 
 
 The principal difference in the composition of the Welsh 
 blue, Welsh purple, and Westmorland green, lies in the 
 varying proportions of iron which they contain. The 
 blue Welsh slate contained 7'83 per cent, of iron in the 
 ferrous state FeO; the purple contained 14 per cent, of 
 iron in the ferric state Fe./> 3 ; and the green Westmorland 
 slate contained 9'96 per cent, of iron in the ferrous state. 
 
 It is generally asserted that iron is the agent which 
 determines the colour of the slate, and it has always been 
 laid down that Westmorland slates derive their colour 
 from the presence of iron in the ferrous state, while the 
 purple slates of North Wales derive their colour, like the 
 marls of the Permian Eocks, from iron in the ferric state ; 
 but on examination of the analyses given it will be seen 
 that the iron in the blue Welsh slate is also in the ferrous 
 state, hence it is difficult to determine with any degree of 
 certainty which of the elements plays the most important 
 part in the determination of colour. 
 
 One of the most important points to notice in the 
 determination of the quality of a slate is its porousness, as 
 undoubtedly those slates, other circumstances being equal, 
 are best which absorb the least amount of moisture, for 
 the absorbed moisture not only increases the weight of the 
 slate, but in frosty weather is converted into ice, and swells, 
 with consequences highly detrimental to the soundness of 
 the slate. 
 
 Several experiments have from time to time been made 
 to demonstrate this quality. I will only mention two, 
 which I have made specially for this Paper. 
 
 I took three slates, each having a surface of 144 square 
 inches. I had them all carefully weighed, and then placed 
 in a bath of water. One was taken out after an im- 
 mersion of fifty hours, and after the surface-water had 
 ceased to drip, was weighed again, and I found the weight
 
 100 grains in excess of its original weight. It was then 
 placed before a fire, and in a few minutes the surface was 
 quite dry, and on being put on the scales again was only 
 30 grains in excess of its original weight. The other two 
 slates were in the water 312 hours, and after the surface- 
 water had ceased to drip I placed them on the scale. In 
 the one case the increase in weight was 127 grains, and in 
 the other 200 grains. Both were then placed before a fire, 
 and, as in the first case, the surface was perfectly dry in a 
 few minutes, and on being again weighed one was 8 grains 
 heavier than its original weight, while the other was 
 exactly its original weight. This shows in one case the 
 absence of any absorption, and in the others only a few 
 grains, which may be considered as highly satisfactory. 
 
 It may be taken that the amount of moisture the best 
 Westmorland and Welsh slates may absorb is not suffi- 
 ciently great to make any material difference in their 
 weight, or in the action of frost upon the absorbed 
 moisture ; but there are slates to which, from their flaky 
 and jointy nature, the absorption of moisture is highly 
 detrimental, as the absorbed water when frozen tends to 
 loosen the joints and open the flakes, which process, when 
 frequently repeated, materially damages such slates. These, 
 however, when used in countries less liable to sudden and 
 violent changes in temperature than we are in England, 
 prove as serviceable as the best known slates in this 
 country. There is still another point of importance de- 
 pending upon the compactness or otherwise of the slate. 
 It was shown by the tables of analyses that all slates con- 
 tain varying percentages of iron, some in the ferrous and 
 some in the ferric state. Iron, as you all know, has a 
 great affinity for oxygen, and if the slate be porous the 
 oxygen of the air combines with the iron when in the 
 ferrous state, changing it into ferric, with the result that 
 the colour is altered and decomposition on a small scale is 
 carried on. 
 
 In addition to this there is a further chemical action 
 that takes place, and a much more disastrous one than 
 the changing of ferrous into ferric oxide. As the analyses 
 show, all the slates contain calcic carbonate, and some of 
 them magnesic carbonate. If the slate be sufficiently 
 porous to admit carbon dioxide (Co.,), which is equally 
 prevalent in otherwise pure and impure atmospheres, the 
 carbonates are changed into bi-carbonates, which are 
 soluble in water CaCo 3 + H,Co :t = CaH,(C0 3 ) 2 the natural 
 result of this being that the slate will in time decompose, 
 and its " waterproof " quality be eventually destroyed. 
 
 Some time ago a Swiss scientist contributed a Paper on
 
 14 
 
 Slates to one of the magazines, in the course of which he 
 suggested the following experiment to test the quality of a 
 slate : Reduce the slate to powder, add hydrochloric 
 acid ; if strong effervescence, proof of a bad slate, full of 
 lime. A portion of another slate is taken, and likewise 
 reduced to powder, and placed in a test tube and heated 
 over a Bunsen flame. A yellow sublimate and fumes of 
 sulphurous acids prove the presence of much iron pyrites, 
 consequently a bad slate. 
 
 I am afraid I cannot agree with these conclusions, as 
 my experience, and that of many others, of slates contain- 
 ing both lime and iron pyrites proves the contrary. 
 
 The analyses I have given show the presence of lime 
 in all the slates which, on the application of HCL., gives a 
 brisk effervescence, and if the above contention be correct, 
 we must classify all these as bad slates, whereas quite the 
 contrary is the fact. 
 
 The best Westmorland slates which we know have stood 
 the action of the atmosphere in some instances at least 
 100 years ; and of some of them it would be safe to state 
 that they have been exposed 200 years, and still show no 
 signs of decay. The same might be said of some slates 
 containing iron pyrites, which would give chemical results 
 pointing, according to this theory, to a bad slate ; but here, 
 again, we are in a position to produce slates heavily 
 charged or permeated with iron pyrites such, for in- 
 stance, as the Ballachulish and Easdale slates, in the 
 North of Scotland, both of which have stood for a con- 
 siderable time, without the least sign of decay from this 
 cause. 
 
 After all, I am much inclined to believe that there is a 
 limit to chemical analysis in the determination of the 
 quality of a slate. The chemical composition of most 
 slates with which we have to deal is very much the same, 
 but we do know that the wearing quality of the various 
 slates differs materially. All this seems to me to suggest 
 the presence of another agent playing an important part in 
 the formation of a slate, and I humbly submit that the 
 meclianicdl arrangement of the particles contained in the 
 slate has more to do with the determination of quality than 
 the best conceived proportions in chemical analysis. 
 
 If we were to take the various elements or ingredients 
 which from analysis we know constitute the best slate, 
 mix all together, and apply sufficient pressure to produce a 
 compact sheet or block, we should not produce an article 
 possessing the same qualities as an ordinary roofing slate. 
 In support of this theory, I beg to mention as an illus- 
 tration the substances known as diamond and graphite,
 
 15 
 
 both of exactly the same chemical composition but differ- 
 ing widely in their properties and ultimate value, which 
 seems to me to point to a different mechanical arrangement 
 of the particles of which the two substances are composed. 
 
 How, then, are we to determine the quality of a slate ? 
 For my part, while acknowledging with gratitude the 
 assistance obtained from the chemical laboratory, I am 
 of opinion that the best and safest of all tests is that of 
 experience. We know from evidence furnished us by 
 buildings erected 80, 100, and even 150 years ago that 
 certain materials have stood the most severe of all 
 tests, that of time ; and until chemical science has dis- 
 covered a more reliable one, we must give time and 
 experience the pre-eminence. 
 
 Amongst those materials I may safely state that none 
 are more conspicuous and none have more highly dis- 
 tinguished themselves in the war with the elements than 
 Westmorland green slates. 
 
 General Description of Westmorland Slate Quarries ; the 
 Method of Preparing the Slates. Cleavage. Architectural 
 value. - The question of cleavage is perhaps one in which the 
 quarry owner is more directly interested than the architect, 
 but a Paper on slates would be far from complete if no 
 reference were made to this subject, and on this ground I 
 crave your indulgence while notifying some of the prin- 
 cipal points coming within our scope under this heading. 
 
 While scientists are mainly interested in discovering the 
 agent or agencies by which cleavage was produced, the 
 quarry owner, on the other hand, is more especially con- 
 cerned in the character of the cleavage in the particular 
 bed of slate he is working, as on the nature of the cleavage 
 depends to a large extent the value of his bed of rock. 
 This property of slate rock by which we are enabled to 
 split it into thin pieces consists of lines or lamination 
 planes running in the direction of the strike of the bed, 
 and always at right angles to the dip of the rock, but 
 cleavage lines occur at varying angles of inclination from 
 the planes of bedding. In Westmorland the cleavage lines 
 are not so well developed as in the slate rocks of North 
 Wales, where it is possible to split a block 2J inches thick 
 into 40 slates equal to ~- d of an inch each in thickness. It 
 would, however, be well-nigh impossible to get from any 
 Westmorland rock an equal number of slates from a block 
 of the same thickness. 
 
 As to the manner in which slaty cleavage was produced, 
 I will merely mention that there are two theories the 
 magnetic and mechanical. 
 
 The former was held by, amongst others, Professor
 
 16 
 
 Sedgwick, in support of which it is pointed out that the 
 direction of the cleavage being N.N.E., coincides with the 
 course taken by the magnetic currents which are passing 
 through the earth. 
 
 On the other hand, it is assumed by a number of emi- 
 nent scientists that cleavage is due to mechanical forces 
 that compressed the sediment at right angles to the line 
 of cleavage. Dr. Sorby, who studied and examined it 
 microscopically and otherwise, states that the " sedi- 
 "ment has been compressed to about one-half of its origi- 
 " nal bulk, and the particles pressed with their flattest 
 " sides towards each other." This arrangement may be 
 seen by grinding a piece of slate thin enough to admit 
 light through it, the particles may be then discerned by 
 the aid of a pocket lens, or to better advantage if placed 
 under a microscope. The specific gravity of Westmorland 
 slates is as follows : 
 
 Green, 2'77. Blue, 2'73. 
 
 If all the slates were split to equal thickness, the differ- 
 ence in weight on roof timbers would be very small, which- 
 ever kind of slate was used. 
 
 The late Bishop Watson gives in his Chemical Essays 
 the result of a series of tests made to determine the weight 
 of a cubic foot of slate, and he found that the difference 
 between a cubic foot of the heaviest and a cubic foot of 
 the lightest of 14 different sorts was only Go oz., or 
 about 5 ^ part of the weight of the heaviest sort. The fol- 
 lowing is a list of the tests : 
 
 Purple Slate. Kentmere, near Kendal . . 27H7 
 
 Pale Blue. Coniston, Waterheacl . . . 2791 
 
 Dark Blue. Troutbeck 2781 
 
 Pale Blue. Thrang Crag 2780 
 
 Pale Blue. White Moss 2779 
 
 Deep Blue. Old Cauldron .... 2778 
 
 Pale Blue Greenish. Near Ambleside . . 2768 
 
 Pale Blue. Ingletou, Yorkshire . . . 2767 
 
 Dark Writing Slate. Bannisdale . . . 2765 
 
 Blackish. Head of Windermere . . . 2758 
 
 Deep Blue. Langdale 2752 
 
 Greenish Blue. Kentmere .... 2750 
 
 Blackish. Cartmell, Lancashire . . . 2740 
 
 Very Pale Blue (fine grained.) Ambleside . 2732 
 
 Medium weight of cubic foot . . . 2767 
 
 It is possible that there may be some present who 
 have not had an opportunity of visiting a slate quarry, 
 and witnessing the process of slate-making, and perhaps
 
 17 
 
 a few descriptive remarks will therefore not be out of 
 place. 
 
 Slate quarries may be divided into two classes, open top 
 and underground. The former, when situate on the hill- 
 side, are generally worked by means of adit levels, through 
 which the slate material and debris are carried out ; but 
 when in the bottom of the valleys are worked " pit " like, 
 and the material for slate working, debris, as well as the 
 water, are hoisted to the surface by means of steam 
 engines or hydraulic machinery. 
 
 As to the best and most economical of these two methods 
 to adopt, much depends on the nature of the rock, and 
 the amount of "top rock" overlying the slate. If the 
 slate rock be capped with a great thickness of "top rock," 
 it will as a rule be cheaper to work the quarry under- 
 ground, as the cost of removing this would be so great as 
 often to render the working unprofitable. On the other 
 hand, by working the quarry " close head," or under- 
 ground, the removal of the" top rock " is dispensed with, 
 but a much larger percentage of the good slate rock is 
 spoiled than in the open quarries, and the work of ren- 
 dering the roof safe is often very costly. 
 
 These are some of the considerations which frequently 
 tax the best energies and resources of the management. 
 
 When commencing slate-making it is necessary in the 
 first place to blast the rock from the cliff-side : this is done 
 by means of a hole varying from | to 1| inch in diameter, 
 according to the size of the piece to be dislocated. The 
 depth of the hole depends on the distance the first joint 
 or " back" may be from the face. The hole being bored, 
 a charge of gunpowder is put in, which is fired by means 
 of a fuse or short straw filled with small gunpowder, 
 having fixed to the end a piece of "match paper." 
 
 The " docker-up " now proceeds to view the dislocated 
 rock, and by means of a hammer and chisel reduces the 
 blocks into smaller and more convenient pieces. They 
 are now loaded into waggons, and either taken out through 
 the tunnels, or hoisted to the surface by the aid of ma- 
 chinery, and delivered in front of the splitting sheds, 
 their final destination prior to being made into roofing 
 slates. 
 
 There is a considerable variation in the size of the blocks, 
 and good judgment, only acquired by experience, is neces- 
 sary to cut them, so as to avoid waste and to the best 
 advantage. Thus a block 6 feet long x 2 feet wide is 
 cut into two pieces of three feet long each ; this is done by 
 cutting a small aperture on one side and applying a series 
 of heavy blows with a wooden mallet on the other side
 
 18 
 
 immediately above the aperture ; by this means the block 
 is cut in two. It is now ready for the splitter. 
 
 There are two methods of splitting in Westmorland, 
 viz. chisel riving and hammer riving, the latter is pecu- 
 liarly characteristic of Westmorland the chisel riving 
 alone being in use in Wales. The chisel-river does his 
 work seated with crossed legs, always putting the left leg 
 over the right; any departure from this is considered 
 slovenly and bad form. He now takes a block, and, rest- 
 ing it on his left knee, proceeds to reduce it to thin slates 
 by the aid of mallet and chisel. The hammer-river, unlike 
 his colleague, works standing. A raised platform or bench is 
 provided on which the block is placed, held by his left hand, 
 while, with the hammer in the right hand, he applies a 
 series of gentle blows along the cleavage planes, with the 
 result that the block is reduced into thin slates. This 
 latter method is much more tedious, and on the whole less 
 expeditious than the former, in addition to which it takes 
 much longer time to become a good hammer-river than a 
 chisel-river. 
 
 I may just mention in passing that at Collyweston, in 
 Northamptonshire, slates are produced which are prepared 
 in a somewhat novel manner. The blocks, which are 
 usually quarried in the autumn, are placed in a position 
 in which the moisture will most readily percolate into the 
 natural joints. The moisture freezes, and the blocks 
 split of themselves into slates suitable for roofing pur- 
 poses. 
 
 As to the antiquity of the slate industry in Westmor- 
 land, it is difficult to find any reliable data ; but it will be 
 perfectly safe to say that quarrying in a crude manner has 
 been carried out for centuries. It is interesting to find, 
 however, that about 100 years ago slates were sent from a 
 Westmorland quarry for Montague House, Whitehall, the 
 Duke of Buccleuch's London residence, from which we 
 may reasonably infer that quarrying had then attained 
 some proportion, and was being carried on more or less 
 systematically ; and it may be mentioned here that when 
 this same house was rebuilt about forty years ago the same 
 slates were used over again, and it was found that they 
 worked out so well that new ones were only sent for the 
 additional area to the roof. 
 
 Up to within about thirty years ago the method of 
 quarrying was, however, still rather primitive, and the 
 quantities produced on a limited scale. This was in a 
 large measure due to the difficulties of transit, want of 
 enterprise on the part of the owners, and what was perhaps 
 worse than all, the reluctance of both masters and men to
 
 adopt the most improved and expeditious methods of pro- 
 ducing. In consequence of this indifference the industry 
 was at one time in great danger of becoming a thing of the 
 past. However, during the last twenty years a remarkable 
 change has been effected in the Westmorland slate trade. 
 The facilities for transit are greatly improved. More 
 energy has been displayed, and more scientific knowledge 
 has been brought to bear upon the working. The newest 
 and most improved methods of production are now em- 
 ployed, with the result that more quarries are in operation, 
 more men engaged, and larger quantities by more than 
 double are produced at this moment, than at any other 
 period in the history of the industry. The outlook for the 
 future is encouraging, the quarries are being deepened, 
 and with increased depth there is always improved quality. 
 The production in the area under our consideration has 
 increased, according to the figures given in the mineral 
 statistics, from 5,309 tons in 1886 to 17,'2<J1 tons in 1894. 
 These figures speak for themselves, and point to the grow- 
 ing popularity of these slates amongst architects, and also 
 to unmistakable activity in the slate trade of the northern 
 counties. From an architectural point of view, Westmor- 
 land Green Slates are exceedingly valuable. There are no 
 slates with which the architect has to deal that will give 
 more satisfaction and produce better effect than these. 
 They possess all the necessary qualities of a good slate ; 
 they are hard and all good slates are hard, although it 
 must not be taken that all hard slates are good. When 
 struck they will give a clear, ringing sound like a solid piece 
 of metal, whilst the sound from an inferior slate is always 
 dull and thick. Their colour is the most beautiful of all, 
 and, especially when used in combination with any build- 
 ing material of a red or terra-cotta shade, produce a most 
 charming effect. Their lasting quality is proverbial ; once 
 a roof is properly covered with Westmorland Green Slates, it 
 is seldom, if ever, any repairs are needed ; and when the 
 building has, owing to age or other circumstances, to come 
 down, the slates are as sound as ever, and with a little 
 dressing may be used over again. Their strength and 
 resisting power are very great ; it takes on an average 
 '20,000 Ib. weight to crush one cubic inch. This quality, in 
 conjunction with their tenacity and elasticity, enables even 
 thin slates to sustain great weight, and gives to them a 
 pre-eminent commercial value for roofing purposes. 
 
 In addition to making good slates, the rock is also 
 capable of being worked for other architectural purposes, 
 in the shape of building and monumental stones of almost 
 every description.
 
 Table of Strata. 
 
 Welsh equivalent 
 i Upper Ludlow. 
 
 LudlowRock, 
 
 Coniston Flags and Grit, 
 Coniston Limestone . 
 
 w <;! itoK 
 w Slates 
 
 Upper Wenlock. 
 = { 
 = Bala Limestone. 
 
 I the Arenig Formation. 
 / Arenig, with perhaps Trema- 
 ={ do(; 8 and Lingula Flags. 
 
 Total production of the different Counties in England, 
 Scotland, and Walt's during the year 1894. 
 
 Value ut 
 
 Quantities Mines or 
 in Tons. Quarries. 
 
 ENGLAND AND WALES 
 
 Breconshire ...... 
 
 Carnarvonshire .... 
 
 Cardiganshire .... 
 
 Cornwall ..... 
 
 Devonshire ..... 
 
 Cumberland ..... 
 
 Denbighshire .... 
 
 Lancashire ..... 
 
 Westmorland 
 
 Leicestershire 
 Merionethshire 
 Montgomeryshire . 
 
 Totals for 1894 . 
 
 previous year . 
 
 241 
 
 12,0 ( .)5 
 
 1,524 
 14,505 
 
 10 
 
 157,816 
 3,257 
 
 573,307 
 447 
 23,565 
 
 5,512 
 4,485 
 
 40,507 
 20 
 
 509,616 
 8,220 
 
 SCOTLAND No returns. 
 
 . 461,673 1,171,366 
 . 438,993 1,107,626 
 
 Quantity and Value of Roofing Slates exported from the 
 United Kingdom in tlie years 1893 and 1894. 
 
 Declared Declared 
 
 Countries to which Exported. Quantities. Value. Quantities. Value. 
 Number. . Number. . 
 
 Norway 121,500 1,458 
 
 Denmark .... 2,411,800 29,158 2,852,700 34,211 
 Germany . . . 30,922,700 141,743 33,465,100 174,951 
 
 Holland . 
 
 Channel Islands 
 France . 
 Canary Island.-: 
 
 1,044,900 
 
 523,700 
 
 1,009,300 
 
 1,012 10,000 27 
 
 1,120 519,600 427 
 
 4,243 570,600 4,481 
 
 1,436 93S.400 2,223 
 
 1,000 48
 
 21. 
 
 1893 
 
 
 1894 
 
 
 Declared ' 
 Countries to which Exported. Quantities. Value. 
 NuinKer. . 
 
 I 
 Quantities. 
 Xunjlirr. 
 
 c. 
 
 Austrian Territories . . 381,800 
 
 898 
 
 401,500 
 
 GUI 
 
 Rouinania ... 
 
 
 
 10,500 
 
 91 
 
 Turkey .... 
 
 3,000 
 
 31 
 
 
 
 
 Boypfc .... 
 
 7,200 
 
 49 
 
 
 
 
 
 West Coast of Africa . 
 
 13,700 
 
 130 
 
 2,000 
 
 26 
 
 St. Helena . 
 
 
 
 
 2,400 
 
 81 
 
 British Possessions in Soutl 
 
 
 
 
 
 Africa. 
 
 500,500 
 
 4,101 
 
 445,300 
 
 3,578 
 
 British East Indies 
 
 R,700 
 
 816 
 
 84,600 
 
 568 
 
 Australasia . 
 
 1,374,400 
 
 
 021,5(10 
 
 7,001 
 
 British West India Island 
 
 
 
 
 
 and Guiana . . . 97,6(10 
 
 73] 
 
 87,000 
 
 280 
 
 Foreign West Indies . . 25,300 
 
 15(1 
 
 U,70Q 
 
 135 
 
 Mexico 2,000 
 
 8 
 
 
 
 
 
 Chile 
 
 
 
 9,000 
 
 40 
 
 Brazil 19,000 
 
 124 
 
 3,600 
 
 53 
 
 Argentine Republic 
 
 
 
 55,000 
 
 443 
 
 . 38,739,100 203,729 40,459,000 230,813 
 
 Total production of the different Counties in England, 
 Scotland, and Wales during the year 1886. 
 
 ENGLAND AND WALES 
 Breconshire .... 
 Cardiganshire 
 Carnarvonshire 
 Cornwall .... 
 Cumberland .... 
 Denbighshire 
 
 Devonshire .... 
 Durham .... 
 Lancashire and Westmorland 
 Leicestershire 
 Merionethshire 
 Montgomeryshire . 
 Somersetshire 
 Yorkshire 
 
 SCOTLAND 
 Argyllshire . 
 Dumbartonshire 
 Perthshire 
 
 Totals for Great Britain for 188C 
 Totsds for 1885 . 
 
 Quantities 
 
 Value at 
 Mines or 
 
 in Tons. 
 
 Quarries. 
 
 89 
 
 112 
 
 155 
 
 349 
 
 . 250,952 
 
 619,493 
 
 . 11,840 
 
 21,415 
 
 1,954 
 
 8,908 
 
 3,016 
 
 4,603 
 
 1,070 
 
 1,055 
 
 1,469 
 
 1,005 
 
 3,355 
 
 6,509 
 
 500 
 
 1,000 
 
 . 144,034 
 
 408,181 
 
 1,058 
 
 2,130 
 
 1,000 
 
 2,000 
 
 . 17,161 
 
 8,370 
 
 437,653 1,080,180 
 
 17,855 
 500 
 700 
 
 18,555 
 
 24,689 
 1,000 
 1,400 
 
 27,089 
 
 456,208 1,107,169 
 468,954 1,175,772
 
 22 
 
 Quantities and Value of Slates exported from the United 
 Kingdom during the years indicated. 
 
 Year. 
 1877 
 1878 
 1879 
 1880 
 1881 
 
 1884 
 1885 
 
 1898 
 1894 
 
 Number. 
 
 87,565,282 
 
 24,268,500 
 
 27,801,100 
 
 31,189,500 
 
 38,415,100 
 
 47,366,300 
 
 84,544,400 
 
 49,085,600 
 
 45,482,000 
 
 43,389,700 
 
 38,739,100 
 
 40,459,000 
 
 Value. 
 .294,515 
 
 183,915 
 170,533 
 212,699 
 250,226 
 192,257 
 251,824 
 242,484 
 227,648 
 203,729 
 230,813 
 
 Quantities and Value of Roofing Slates exported from the 
 United Kingdom in 1885 and 1886. 
 
 
 
 Declaral 
 
 ,~ 
 
 Declared 
 
 Countries to which sent. 
 
 Quantities. 
 
 Value. 
 
 Quantities. 
 
 Value. 
 
 
 Number. 
 
 . 
 
 Number. 
 
 . 
 
 Russia 
 
 
 
 
 
 9,500 
 
 S3 
 
 Sweden 
 
 60,500 
 
 574 
 
 
 
 
 
 Norway 
 
 10,200 
 
 70 
 
 
 
 
 
 Denmark .... 
 
 2,442,300 
 
 27,888 
 
 1,846,000 
 
 19,197 
 
 Germany .... 
 
 31,279,100 
 
 148,952 
 
 31,828,700 
 
 155.962 
 
 Holland 
 
 307,100 
 
 913 
 
 301,000 
 
 1,1104 
 
 Belgium 
 
 373 800 
 
 268 
 
 5(!7,(H)0 
 
 623 
 
 Channel Islands . 
 
 595,700 
 
 4,139 
 
 532,500 
 
 3,764 
 
 Prance 
 
 1,571,500 
 
 3,291 
 
 79(1,000 
 
 1,118 
 
 Spain 
 
 
 
 
 7,300 
 
 49 
 
 Gibraltar .... 
 
 1,800 
 
 22 
 
 6,000 
 
 60 
 
 Austrian Territories . 
 
 680,900 
 
 1,592 
 
 1,498,600 
 
 3,602 
 
 Turkey 
 
 4,000 
 
 75 
 
 
 
 
 
 West Coast of Africa . 
 
 40,901 
 
 259 
 
 8,500 
 
 74 
 
 British Possessions in South 
 
 
 
 
 
 Africa 
 
 291 500 
 
 1 646 
 
 197,200 
 
 1,067 
 
 British East Indies 
 
 69,900 
 
 590 
 
 6,000 
 
 43 
 
 Australasia . 
 
 7,491.9(10 
 
 49.581 
 
 5,433,800 
 
 38,1177 
 
 British North America 
 
 
 
 
 
 6,000 
 
 34 
 
 U.S. of America on the 
 
 
 
 
 
 Atlantic .... 
 
 
 
 
 
 34,900 
 
 132 
 
 British West India Islands 
 
 
 
 
 
 and Guiana 
 
 . 
 
 
 
 14,500 
 
 104 
 
 Foreign West Indies . 
 
 5,000 
 
 44 
 
 
 
 
 
 Brazil 
 
 
 
 
 
 12,000 
 
 80 
 
 Uruguay .... 
 
 3,000 
 
 28 
 
 
 
 Argentine Republic 
 
 252,900 
 
 2,366 
 
 291,200 
 
 2,280 
 
 i;!.::s'.i.7uO 227,648
 
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