;28 
 18 
 
 NRLF 
 
 tat 
 
ift valleys o 
 rn Sinai. 
 
BERKELEY 
 
 LIBRARY 
 
 UNIVERSITY OF 
 CALIFORNIA 
 
 - 
 
 EARTH 
 
 SCIENCES 
 
 LIBRARY 
 
THE 
 
 RIFT VALLEYS & GEOLOGY 
 OF EASTERN SINAI. 
 
 BY 
 
 W. F. HUME, D.Sc., A.R.S.M., F.G.S. 
 
 READ BEFORE THE INTERN A TIONAL GEOLOGICAL CONGRESS, 
 PARIS, AUGUST, 1900. 
 
 LONDON : 
 
 DULAU & CO., 37 SOHO SQUARE, W. 
 1901. 
 
H~\ C. O 
 
 K^ 
 
 EARTH 
 
 SCIENCF 
 
 LIBRARY 
 
 LONDON: PRINTED BY STBANGEWAYS AND SO 
 TOWER STEEET, CAMBRIDGE CIRCUS, W.C. 
 
INTRODUCTION. 
 
 OWING to the kind permission granted me by the 
 Egyptian Government through Sir W. Garstin, 
 Under-Secretary of State for Public Works, and Captain 
 H. G. Lyons, R.E., Director of the Survey Department, I 
 am enabled to lay before you a brief statement of certain 
 results obtained in the course of the Survey of Eastern 
 Sinai during the season of 1898-99. The following 
 remarks are based upon the admirable map prepared by 
 Mr. H. G. Skill, F.R.G.S., who spared no pains to obtain 
 as exact a picture of the country as was possible in the 
 time at disposal. Unfortunately, this map has still to 
 await publication, as there are many others of earlier date 
 to be compiled and printed. 
 
 Eastern Sinai has been remarkably neglected by the 
 many scientific writers and travellers who have visited the 
 holy mountain, most of them contenting themselves with 
 an examination of the western side of the peninsula, or 
 with a rapid traverse through the region from Sinai to 
 Akaba, this being especially the case with the south-eastern 
 corner between Dahab and Sherm, an area of which much 
 will be said in the present paper. The only travellers of 
 note in this district, before 1842, appear to have been 
 Riippell and Burkhardt, and in 1847 Russegger published 
 a map of Syria and Arabia Petrea, which has, at least, the 
 merit of suggesting the mountainous character of the 
 country, and shows one long valley running parallel to the 
 
 462676 
 
4 The Rift Valleys of Eastern Sinai. 
 
 general outline of the Gulf of Akaba, from near Noweiba 
 to Nebk. 
 
 In 1868 the Rev. F. W. Holland, M.A., one of the 
 members of the Ordnance Survey, which made an excellent 
 survey of the western side of the peninsula, under the 
 direction of Sir C. Wilson and Captain Palmer, published 
 a small map in the Proceedings of the Royal Geographical 
 Society, which appears to have remained the standard 
 since that date, and to have been adopted for the interior 
 of the country in the Admiralty Chart of the Red Sea, 
 the result being a curious topographical contrast between 
 the east and west sides the latter taken from the 
 Ordnance Survey which it is hoped will disappear when 
 our own contribution is printed. Professor Hull's fault 
 region touches our district to the north, he having crossed 
 by the usual Akaba route. 
 
 TOPOGRAPHY OF EASTERN SINAI. 
 
 The traveller who enters Sinai by the quarantine port of 
 Tor, will, when standing on the shore and looking eastward, 
 see a prominent mountain range running roughly north-west 
 and south-east, and extending as far as eye can reach in 
 both directions, broken here and there by more prominent 
 summits, among which the many-peaked Serbal in the 
 extreme north, the dark plateau massif of Catherina or 
 Zebir, and the bold peak of Um Shomer, opposite Tor, are 
 especially conspicuous. This great range is the western 
 edge of the region, which will be dealt with in this paper, 
 and is itself a relic of a tectonic change of the first magni- 
 tude. Professor Fraas, in an eloquent passage (A us dem 
 Orient, p. 7), has referred to it ' as rising, since the beginning 
 of things, out of the ocean, untouched by Silurian or 
 Devonian, by Dyas or Trias, by Jura or Cretaceous ; only 
 
The Rift Valleys of Eastern Sinai. 5 
 
 round the foot of it has the Red Sea drawn a crown of 
 corals/ yet we now know that it represents the upthrow 
 side of a magnificent fault which at the western foot of 
 Serbal has a throw of at least 1500 metres, the granite wall 
 rising over 1250 metres above the plain of El Gaa, while 
 uptilted Cretaceous marls and limestones form low 
 hillocks, or white plateaux, at its foot (see Walther, J., 
 Korallenriffe der Sinaihalbinsel, p. 452) itself certainly 
 post-Eocene in age, and, from comparison with the Red 
 Sea Hills, probably only originating during the Pliocene. 
 On this point, however, Mr. Barron, who studied the 
 western side of the peninsula, will, no doubt, have much of 
 interest to tell in the future. The main range, in reality, 
 consists of a series of narrow crests, separated by but few 
 high mountain passes, and only traversable, by heavily 
 loaded camels, at two points, viz : up Wadi Isleh and 
 across the Tarfah Pass, into Wadi Nasb, and through 
 Wadi Hebran to Wadi Solaf and Wadi Feiran while it 
 gradually descends in level from Zebir and Um Shomer, 
 over 2500 metres, to about 1500 metres in Sahara, then 
 rapidly dying away towards Ras Muhammed. It may be 
 mentioned in passing, that the watershed but seldom agrees 
 with the principal chain, lying to the east of it, north of 
 Eth Thebt, while to the south most of the higher summits 
 are on its eastern side. 
 
 If this range be crossed, and Sinai itself ascended, the 
 view to the east is decidedly disappointing. To the north- 
 east is seen the long white limestone wall of Jebel Gunneh 
 running more or less east and west, and far to the east, 
 breaking into isolated masses, ending with the fine trun- 
 cated cone of Jebel El Ain. In front of and parallel to 
 it extend the sandy plains and precipitous plateaux of 
 sandstone, cut into deep ravines meandering in all 
 directions, while still nearer is an apparently flat or 
 
6 The Rift Valleys of Eastern Sinai. 
 
 undulating granite plateau, out of which the Derawi Er 
 Roghah ridge, the dark peak of Habshi, and a few lesser 
 heights, rise as isolated projections. 
 
 To the south-west extends a mountain wall, which 
 hides all the southern land from view, and constitutes the 
 most important scenic feature in Eastern Sinai, extending 
 across the country from the Central Range to the Gulf of 
 Akaba, where it forms a precipitous ridge close to the 
 sea-shore. This Transverse Divide claims special attention 
 not only from the fact that it separates two different types 
 of country, but also because, at least on the western side, 
 these two regions are at very different levels, there being 
 an abrupt fall to the south. In general the Transverse 
 Watershed and Range are identical at all important points, 
 the main characteristic being the gradual lowering in 
 height from west to east. 
 
 Thus Fersh Sheikh El Arab, near the Central Range, is 
 over 2000 metres, while Jebel Gnai, close to the Gulf of 
 Akaba, is only 1000 metres high, the watershed itself being 
 thrown into striking curvatures, due to causes which will 
 shortly be considered. There are only five passes over 
 this divide, two of which are easy, while the remainder can 
 only be negociated by lightly loaded camels, and on these 
 special stress is here laid, because they all have one 
 remarkable feature in common, viz. : That the valleys 
 they connect form five roughly straight lines, all parallel to 
 one another and to the Gulf of Akaba, that is running in a 
 direction somewhat west of south. 
 
 What then is the origin of this structure and what 
 characters do these depressions present ? 
 
 We will at first examine two which are already to some 
 extent outlined on the existing map, and to which the 
 names of Um Raiyig-Shelala and Melhadge rifts have 
 been respectively applied, these, it will be easy to show, 
 
The Rift Valleys of Eastern Sinai. 7 
 
 belong to the category of Rift Valleys, of which the Gulf 
 of Akaba itself is a well-known and striking example, 
 and are the effects of dynamical changes whose char- 
 acter, extent, and possible age may be more or less 
 accurately determined. It may be recalled that these 
 are not necessarily single depressions, but rather a series 
 of basins separated by barriers, which, though higher than 
 the main valley, are of no great altitude compared with 
 the bordering hills. 
 
 There are, as has been said, two main longitudinal 
 valley-systems of this kind in Eastern Sinai, both crossing 
 and extending far north and south of the Transverse 
 Divide, and of these the Um Raiyig-Shelala rift will 
 first be dealt with. 
 
 In descending Wadi Nasb, the scenery of the granite 
 region is for the most part of a fine character, bold hills 
 scored by wild gorges filled with boulders bounding the 
 deep and narrow ravine, which in part has a flat sandy 
 floor, grooved only by shallow dry water-courses, while at 
 other spots groves of tamarisk and palm, or jungles of 
 weeds and rushes give an additional touch of beauty, and 
 the effect of contrast is therefore very striking when, at 
 the gates of Nasb, the way is suddenly barred by dark- 
 green hills of softer outlines, and a valley is seen running 
 at right angles to the previous course in a T-shaped 
 manner. This change in the geology and topography is 
 too marked to escape the most casual observer, but 
 another point speedily arrests attention, a small mass of 
 yellow sandstone being seen to rest on the opposite 
 side of the valley against the igneous hills, which rise 
 600 metres above it. The interest of this occurrence is 
 enhanced when it is found that the nearest Nubian 
 Sandstone to the north is 25 kilometres distant, and 
 this occurs not in the valley, but capping a granite 
 
8 The Rift Valleys of Eastern Sinai. 
 
 plateau. Turning down Wadi Shelala to the south, the 
 same sandstone first rests on the western side, and finally 
 blocks the way, stretching across the valley as a barrier 
 of brilliantly variegated or dazzling white colour rising as 
 a cliff 100 metres high, and forming the watershed at this 
 point. 
 
 A later study of the distribution of the Nubian Sand- 
 stone showed that this relic, which has all the typical 
 features of the rock of the main plateau to the north, has 
 been let down for at least 700 metres, the height of the 
 igneous hills which rise above it on both sides. Crossing 
 the ridge, the rift is seen to continue south in an almost 
 
 Nub. 
 
 /Sandstone. 
 
 N.s.:3_ . i-% _. ....._. .. 
 
 Granite 
 Fig. i. 
 
 perfectly straight line, but crossed at oblique angles by 
 transverse valleys, south of which in each case is a low 
 pass, so that the furrow is not one continuous valley, but 
 several, separated by low watersheds. After crossing the 
 great drainage line of Kyd, the rift is finally cut off by 
 Wadi El Tema, which curves round to join Wadi Kyd 
 through Wadi El Beda. 
 
 Returning and proceeding northward from the gates of 
 Nasb, the only striking feature at first is the steepness of 
 the bounding walls, which rise 500 metres on each side, 
 and it is not till the head of Um Raiyig which continues 
 the north trending loop of Nasb is reached, that another 
 point of special interest is rioted, where a ridge of lime- 
 stone with white sandstone at the base, almost absolutely 
 
The Rift Valleys of Eastern Sinai. 9 
 
 blocking the road and being enclosed between two walls of 
 Nubian sandstone resting on granite, forms the hill of 
 Um Raiyig (see fig. i). 
 
 On the northern side of this valley the depression still 
 continues to the foot of the Cretaceous limestone plateau, 
 the normal boundary being the Nubian sandstone either 
 resting on granite or occupying the whole of the low cliff 
 the height of the boundary walls rapidly diminishes to the 
 north of Wadi Nasb but in the rift itself different 
 conditions prevail, there being the curious combination 
 of an outlier and inlier in close proximity to one another, 
 for on leaving Um Raiyig and proceeding northward after 
 passing a second Cretaceous hill, we are suddenly face to 
 face with a sharp granite crest, running north and south, 
 and rising steeply through the surrounding sedimentaries. 
 It is thus seen that the Shelala-Um Raiyig rift is charac- 
 terised by : 
 
 1. Its length, being about seventy-two kilometres long. 
 
 2. Its almost perfectly straight character, there being 
 only a very slight bend where Wadi Nasb turns east, at 
 the mouth of Um Raiyig. 
 
 3. By the steep slopes of the bounding hills throughout 
 the greater part of its course. 
 
 4. By the occasional diversity of geological structure 
 on both sides, especially marked where it separates the 
 granite range of Ashara from the felsitic hills of Ferani. 
 
 5. By the letting down of younger beds along this line, 
 so that strata have been displaced from 200 to 600 metres 
 at least, the result being that both Cretaceous limestone 
 and Nubian sandstone exposures occur far south of their 
 main outcrop. 
 
 6. The presence of older granites surrounded by the 
 younger sedimentary rocks. 
 
io The Rift Valleys of Eastern Sinai. 
 
 Raib-Melhadge Rift. This second rift has again a 
 striking effect on the features of the country, arid is 
 longer than the previous one ; but does not have marked 
 rift characters throughout its whole length, though 
 sufficient for Russegger's map to show it as an un- 
 broken valley extending from north of Dahab to 
 near Nebk. The first point that strikes the traveller 
 going from Ain El Hudera to Dahab through Wadi Raib 
 erroneously named Wadi Zal by Holland is the fact 
 that the granite range extends far further to the north 
 on its eastern than on its western border, a feature well 
 brought out in Russegger's map. The eastern and western 
 sides of the upper part of this valley are also in sharp 
 contrast, the former being a continuous steep wall, while 
 on the west the country is geologically far more complex, 
 and has clearly undergone considerable disturbance. 
 Cenomanian limestone ridges and plateaux of Nubian 
 sandstone, the latter capping masses of granite, succeed 
 each other in a way that shows the whole to be the 
 result of folding and step-faulting. 
 
 Fig. ?. 
 
 Thus, in one place, a side valley, Wadi Um Rowah, 
 the features present are seen to be due to the breaking 
 down of an anticlinal fold, the centre having been step- 
 faulted. On both sides of the valley are low granite 
 slopes G.N. (see fig. 2) capped by the dark-red sand- 
 stones here named Lower Nubian L.N. at the foot of the 
 cliff being lower plateaux of the same rock. The centre of 
 the valley is occupied by rocks of much younger age, 
 
The Rift Valleys of Eastern Sinai. 1 1 
 
 ridges of Cenomanian limestone C.L. and the white grits 
 of the Upper Nubian U.N. -being present below the level 
 of the granite in the bounding walls. To produce this 
 result there must have been a displacement of at least 200 
 metres. In the main valley itself the result is still more 
 striking, for there Cretaceous limestones form a low ridge 
 dipping steeply eastward towards the granite which rises 
 immediately above it to a height of over 300 metres. 
 Descending Wadi Raib the conditions become simpler, 
 and the nature of its origin becomes more and more 
 evident, the Nubian on the west giving way to granite 
 cliffs, and the valley becoming a broad highway bounded 
 on both sides by precipitous heights. Yet scattered all 
 along its course are low hills of white Nubian sandstone, 
 and in one place Cenomanian limestone, so that the sur- 
 prising result is realised, that Cretaceous fossils are collected 
 from a limestone on botJi sides of which tower granite 
 cliffs to a height of over 500 metres, the extent of dis- 
 location being here at least 700 metres. 
 
 There is thus no question that Wadi Raib, and its 
 extension in the eastern loop of Wadi Nasb, is undoubtedly 
 a rift, while its parallelism to the Um Raiyig line and 
 the Gulf of Akaba shows them to have all been formed 
 as part of the same movement. At the mouth of Wadi 
 Abuksheib, where the last Nubian outlier a fine mass 
 100 metres high is met with, and beyond that point, 
 the fissure character disappears in the low granite country, 
 though the valleys forming the main road to Sherm run 
 parallel to the Gulf of Akaba, and are the only ones 
 available for camels. At the head of the Wadi Gnai, 
 which trends north and south, the transverse divide is 
 crossed by a low pass, from the south of which extends 
 the long and narrow furrow of Melhadge cutting in a 
 straight line through a dark range of metamorphic hills, 
 
12 The Rift Valleys of Eastern Sinai. 
 
 which rise on both sides to heights of from 300 to 500 
 metres. Those on the east are of special interest, because 
 they form a well-defined Coast watershed, running parallel 
 to the rift. This watershed is, however, not continuous, 
 in the low granite country near Nebk being broken through 
 by the two large valleys of Kyd and Um Adowi, and 
 further south, near Letih, being only formed by a gravel 
 terrace six metres high. As the central chain is ap- 
 proached, it again becomes conspicuous, attaining its 
 maximum height in the bold projecting spur of Jebel 
 Haimar. Holland failed to recognise this, for he speaks 
 of finding an easy way across the head of several valleys 
 running to the Gulf of Akaba, whereas he would have had 
 to cross a pass in each case, had he tried to reach the 
 sea by their means. Similarly, he has made Wadi Letih 
 run out to the south towards Sherm, whereas it is deflected 
 north by this watershed, and becomes a tributary of Um 
 Adowi. The north and south trending depression can be 
 traced as far as, and including, a portion of Wadi Letih, 
 broken only by the insignificant transverse divide of 
 Wadi Merari. 
 
 Of the remaining three rifts, one lying half-way 
 between the two just mentioned, though lost in the Nubian 
 sandstone district to the north, runs as a deep furrow 
 through the granite plateau north of Wadi Nasb, and 
 crossing the latter valley forms the eastern boundary of 
 the Ferani range, while finally it bends south-east in 
 Wadi Madsus, and cuts through the schistose hills. Here 
 again, the depression is bounded throughout the greater 
 part of its course by steep walls, and crossed by 
 several low ridges, in one of which, between Wadi Um 
 Shokeh and Abuksheib, a small inlet of Nubian sandstone 
 is still preserved. The other two possible rifts are deter- 
 mined as such by their parallelism to those previously 
 
The Rift Valleys of Eastern Sinai. 1 3. 
 
 described, but their northern extension has not been 
 surveyed, while they are both cut off to the south by the 
 transverse line of Wadi Kyd. These valleys lie to the west 
 of the Shelala fracture at a far higher level than the latter, 
 and do not contain traces of younger beds let down ; but 
 sufficient has been said to show that a system of rifts 
 parallel to the Gulf of Akaba has given rise to the most 
 important longitudinal valleys in Eastern Sinai, where 
 their presence does not seem to have been previously 
 suspected, Hull only showing faults further to the north. 
 Though viewed from a distance, it seems probable that 
 rifts of similar nature are developed on a still grander 
 scale on the eastern side of the gulf, a broad plain 
 apparently separating two remarkably precipitous ranges 
 of mountains. 
 
 ORIGIN AND CORRELATION OF THE EAST SINAI RIFTS 
 WITH THOSE OF NEIGHBOURING DISTRICTS. 
 
 As the Eastern rifts form but parts of a complex system 
 it is necessary to consider their relation to those on the 
 western side, and in regions immediately adjoining, before 
 their age and origin can be adequately discussed. 
 
 Glancing at the map of the Ordnance Survey, an 
 important line is observable running close to 34 E. 
 longitude in a north-south direction, which extends over 
 20' of latitude, and is throughout traversable by baggage 
 camels. 
 
 The explored portion of this depression opens in the 
 north with the remarkable break of El Watiyeh, a cleft 
 across a solid granite wall trending slightly east of north. 
 From here Wadi El Sheikh runs south in an almost 
 perfectly straight line, and from its continuation in Wadi, 
 
14 The Rift Valleys of Eastern Sinai. 
 
 Sebaiyeh, an easy pass leads into Wadi Rahabeh, and 
 another forms a connection with Wadi Tarfah. At the 
 junction of the latter with Wadi Isleh, this straight 
 character disappears, but Wadi Eth Themnin and Theman, 
 separated by a narrow col, are not far removed from the 
 dominant direction, and may possibly be referable to the 
 same movement. The importance of this line lies chiefly 
 in the fact that it is practically the separation between two 
 differently trending systems of connected valleys, the 
 Akaba type above mentioned being to the east, while to 
 the west is the Suez, or N.W.-S.E. type. A study of the 
 Ordnance map of Sinai shows that such a line is roughly 
 outlined from Wadi Entish through Wadi Sheiger and 
 Hargus, close to the limestone escarpment, but a still 
 more striking example is the one which, beginning 
 with Wadi Suwig in 29 2' North latitude, crosses the 
 head of Tayiba, and forming many connected valleys, 
 viz., Lebweh, Berrah, &c., at length reaches the granite 
 wall bounding the Central Sinai range on the north. It 
 is therefore of the highest interest to find that the 
 Nagb Hawa pass, the only other entry into the Sinai 
 region besides El Watiyeh. is precisely on the pro- 
 longation of this line, the rift being further continued 
 in the plain of the Law, Er Rahab, the convent valley, 
 and so over a low pass to Es Sheikh. 
 
 How completely the existence of these dislocations 
 in the Central Sinai region were unknown is best seen by 
 reference to a compilation of our knowledge on the subject 
 brought together by Dr. M. Blanckenhorn, under the 
 title 'Die Strukturlinien Syriens und des Roten .Meeres,' 
 in the Festschrift in honour of Baron von Richthofen, 
 Berlin, 1893, where not a single one of the rifts above- 
 mentioned is suggested. 
 
 An examination of the western coast of the Red Sea 
 
The Rift Valleys of Eastern Sinai. 1 5 
 
 and Arabian desert generally, by my colleague, Mr. Barron, 
 and myself, emphasises the enormous importance of 
 the N.W.-S.E. Suez system of rifts, these having ap- 
 parently given rise not only to the abrupt western slope 
 of Sinai and the Gulf of Suez itself, but also being the 
 cause of the steep mountain barrier of the Red Sea hills, 
 and of the two perfectly parallel igneous ranges Esh, &c., 
 and Zeit which lie between it and the gulf. The same 
 series of dislocations have probably given rise to longi- 
 tudinal drainages in the centre of the Red Sea hills west 
 of Abu Harba and the Gattar range, there being a road 
 running up the centre of the northern Red Sea hills at 
 present unexplored. Nor is it difficult in glancing at 
 Zittel's geological map of Egypt based on Schwein- 
 furth's work to recognise the general parallelism of 
 Wadi Qena and even, in fact, of the Nile valley itself, 
 to the dominant trend. 
 
 On the east of the north-south Es Sheikh line prac- 
 tically longitude 34" E. as has been stated above, the 
 Akaba type is alone present as far as our experience goes, 
 though the faults shown by Hull north of latitude 29 N. 
 in Eastern Sinai are indicated as absolute due north and 
 south. Personally I am inclined to think that a re- 
 investigation would show them really to lie somewhat 
 east of north, parallel to the Gulf of Akaba. On the 
 eastern side, as has already been remarked, the fine 
 precipitous ranges of Midian visible from the Sinai side, 
 with the broad plain which runs parallel to them, must in 
 all probability have the same character, the Akaba rift- 
 system being to this country what the Suez type is to 
 Egypt. Unfortunately this portion of Arabia is not at 
 present readily available for scientific investigation. 
 
 There is a third type of dislocation which has not yet 
 been described, but which may nevertheless play a not 
 
1 6 The Rift Valleys of Eastern Sinai. 
 
 unimportant part in the structure of the peninsula. 
 Attention has been called by Walther ' Die Korallenriffe 
 der Sinai Halbinsel,' vol. xiv., Abhandl. Math. PJiys. 
 Classe Konigl. Sacks. Gesell. der Wissenschaften basing 
 himself on the Admiralty charts of Nares and Moresby 
 to the threefold character of the Red Sea, Gulf of Suez, 
 and Gulf of Akaba, respectively, and also to the remarkably 
 sudden increase in depth south of the Straits of Jubal, 
 which join the Gulf of Suez and Red Sea, a similar sharp 
 difference being noted at the mouth of the Gulf of 
 Akaba. Here Blanckenhorn has drawn a transverse 
 fracture south of Tiran Island, and Hull has shown 
 similar east and west faults north of latitude 29 N. 
 at right angles to his north and south displacements. 
 
 It is scarcely to be supposed that South-Eastern Sinai 
 would escape taking part in movements of this nature, 
 and, as a matter of fact, several important physical features 
 must be directly due to their existence. Their most 
 prominent result is probably the Transverse Divide itself, 
 the general level of the country to the north of this 
 physical feature being higher than that to the south. 
 Similarly the broad spurs and transverse chains which 
 run from the central range have had the same origin, and 
 Jebel Zafara, south of Sherm, is undoubtedly the result 
 of a transverse fault In this connection, a notable feature 
 is the regularity and parallelism of the valley directions, e.g., 
 other than the longitudinal rifts already mentioned. Thus, 
 east of the main chain, 17 out of 25 valleys show a decided 
 south-eastward trend, these all entering the Gulf of Akaba. 
 On the other hand, six others mapped follow a north-east 
 course, these being all situated north of the Transverse 
 Divide, and west of the Um Raiyig-Shelala rift, against 
 which they terminate abruptly. In fact, the following 
 generalisation will not be far from the truth, viz., that in 
 
The Rift Valleys of Eastern Sinai. 17 
 
 the space between the divide, the Es Sheikh and the 
 Shelala rifts, the valley directions are normally either 
 slightly east-of-north, west-of-south, or north-east, while in 
 all other parts of the peninsula the dominant valleys 
 trend slightly east-of-north, west-of-south, or south-east. 
 
 It may be mentioned that on the opposite or western 
 side of the main chain, the valleys trend north-west, south- 
 east, or south-west. Many of these valleys on both sides 
 are distinguished by the fine character of their gorges, 
 this being especially true of the valleys north of the 
 transverse divide, Wadis Nasb and Goura being deep 
 fissures, on both sides of which rise precipitous hills over 
 600 metres high. 
 
 PRINCIPAL SUMMARY AND GENERAL STATEMENT 
 OF THE STRUCTURE OF EASTERN SINAI. 
 
 The principal results of this investigation may thus be 
 brought together. 
 
 1. The main mountain range from Sinai to Eth Thebt 
 does not in general agree with the Central Watershed, 
 but the latter is usually a short distance to the east 
 of it. 
 
 2. The chief mountain line from Eth Thebt to Ras 
 Muhammed seldom agrees with the Central Watershed, 
 but the latter in the main lies to the west of it. 
 
 3. The main Sinai Peninsula mountain system consists 
 of a series of long crests separated by high passes 
 trending N.W.-S.E., and gradually lowering from 2600 
 metres in the north to sea-level at Ras Muhammed. 
 The principal chain is bordered by a secondary longi- 
 tudinal system, lower than the former in the northern 
 half of the area, but, together with the east-west spurs 
 running from it, rivalling it in the southern half. From 
 
 B 
 
1 8 The Rift Valleys of Eastern Sinai. 
 
 Wadi Hebran to Ras Muhammed only two easy passes 
 cross the chain. 
 
 4. East of Fersh Shiekh El Arab, a Transverse system 
 runs from west to east to the Gulf of Akaba, the general 
 level of the country to the north of it being higher than 
 that to the south. This is formed of a series of hill 
 masses, at Fersh Sheikh El Arab 2100 metres high, and 
 lowering to about 500 metres near the gulf. 
 
 5. The Transverse Watershed is identical with the 
 Transverse Chain at most of the important points. 
 
 6. The Transverse Chain is crossed by five passes 
 two available for baggage camels which have this 
 remarkable feature in common, viz., that the valleys they 
 connect form five roughly straight grooves, all parallel to 
 one another and to the Gulf of Akaba , e.g., in a direction 
 somewhat east of north or west of south. 
 
 7. A Coastal Watershed broken at two points runs close, 
 first to the Gulf of Akaba, and then to the Central plain, 
 until it joins the spur of Haimar running out from the 
 main chain. 
 
 8. The Transverse Chain separates two districts : 
 a Northern, still retaining much of its original plateau 
 character, and having an average level of over 1200 metres, 
 except where it is cut through by deep narrow gorges ; and 
 a Southern, cut up into a multitude of ranges and peaks, 
 the valleys at whose bases only reach 1000 metres at the 
 foot of the main chain. 
 
 9. In consequence of the above, the northern moun- 
 tains though absolutely higher, are relatively lower above 
 the valleys rarely exceeding 600 metres than the 
 southern ones, which commonly rise from 600 to 1200 
 metres above the valleys at their base. 
 
 10. Within the hill-districts, the superior hardness of 
 igneous dykes has been the cause of a special form of 
 
The Rift Valleys of Eastern Sinai. 19 
 
 country dyke-country in which the harder dykes parallel 
 to each other have given rise to parallel ridges, separated 
 by shallow valleys. 
 
 11. All the main south-eastern mountain ranges are 
 included between the above watersheds, outside being 
 either foothills, coastal plain, or merely fringing coral 
 reef. 
 
 12. The three principal eastward trending valleys 
 stand in sharp contrast to each other : thus, Wadi Nasb 
 receives almost all its drainage from the north ; Wadi 
 Kyd drains the country both to north and south ; while 
 Wadi Um Adowi receives all its tributaries of note from 
 the south only. 
 
 13. There are six north and south valleys, each con- 
 sisting of deep depressions bounded by steep-sided hills, 
 running in a straight line, and, by the presence of younger 
 strata at their base, showing direct geological evidence of 
 their rift origin. 
 
 14. Three dominant valley directions are noticeable. 
 South of the Transverse Chain the valleys runs south- 
 east : north of that chain and west of the Shelala rift, 
 north-east, while the third system is that above-mentioned. 
 
 15. In contrast with these, on the western side of the 
 main chain the predominant direction is north-west, south- 
 east in the north of the peninsula, and soiith-west on the 
 south-western side of the main chain. 
 
 GENERAL CONCLUSION. 
 
 The principal features of Southern Sinai have been 
 produced by dislocation rather than erosion, fracture in 
 three directions, either directly proved or in the highest 
 degree probable, having determined the general structure 
 of the country. 
 
2O The Rift Valleys of Eastern Sinai. 
 
 It is, in fact, the meeting-point of two great longi- 
 tudinal rift-systems, parallel to the Gulf of Suez and Gulf 
 of Akaba respectively, traversed by a third or Transverse 
 type, the result being the apparently intricate maze of 
 sharp crest and deep valley characteristic of this region. 
 
 GEOLOGY OF EASTERN SINAI. 
 
 The importance of the rift-structure in Eastern Sinai 
 having been more specially treated in the first part of 
 this paper, we now propose to touch upon the problems of 
 geological interest on which the district may throw light 
 and which at present may be considered of a contro- 
 versial character. The country to which your attention 
 is directed is that portion of the peninsula of Sinai which 
 lies between the degrees of latitude 27 42' North and 
 29 N., and between longitude 34 East and the Gulf of 
 Akaba. Considered in the broadest sense its geological 
 structure is comparatively simple, the hill districts in the 
 southern half being entirely composed of igneous and 
 metamorphic rocks, which north of Wadi Nasb are capped 
 by Nubian sandstone. In the neighbourhood of Ain El 
 Hudera the latter forms a belt of low plateaux, broad 
 plains and vertically-sided sandstone hills, extending to 
 the foot of the escarpment of Gunneh, which itself con- 
 sists of light Nubian grits capped near the summit by 
 Cenomanian limestones. Owing to the fault and rift 
 formation, this simple succession is considerably disturbed, 
 the result being the production of extremely complex 
 topographical conditions. Apart from those already 
 mentioned the most important feature outside the hill 
 region is the plain between Nebk and Sherm, in which 
 
The Geology of Eastern Sinai. 2 1 
 
 the superficial gravel deposits and coral-reefs are well 
 displayed. North of this expanse similar reefs border the 
 Gulf of Akaba throughout its whole length north of 
 Nebk, forming a strip often only a few metres wide 
 between the igneous ridge and the sea. 
 
 The geology will be considered in the following 
 order : 
 
 1. Pebble gravels, Travertine, &c. 
 
 2. Coral reefs. 
 
 3. Cretaceous limestones of Cenomanian age. 
 
 4. Nubian sandstone. 
 
 5. Igneous rocks, &c. 
 
 I. 
 
 i tf. PEBBLE GRAVELS. 
 
 Nothing will strike the observant traveller more 
 forcibly on entering the narrow gorges in the Sinai hills 
 than the great development of high terraces of gravel in 
 the principal valleys, these being often over 20 metres in 
 height, and composed either of materials of different 
 consistency very roughly stratified, or still more often of 
 the debris of the igneous hills mixed together in a more 
 or less chaotic manner. Fraas was especially impressed 
 by these occurrences, which he could only presume were 
 the moraines left by former glaciers (though as to their 
 age he could say nothing), an idea which is not really so 
 far-fetched as might appear, as even at the present time 
 snow lingers on the summits of the Sinai hills, sometimes 
 for days together. Thus, in December 1898, when we 
 ascended Jebel Sabbagh, it was covered with a coating 
 of snow which had not disappeared after several days of 
 sunshine, the temperature at the summit at mid-day 
 barely exceeding o Centigrade. If the temperature here 
 
22 The Geology of Eastern Sinai. 
 
 were reduced to the same extent as it would be in Europe 
 during the Glacial Period, a small amount of neve would 
 have accumulated in the higher mountains, and the 
 increased torrent-action resulting therefrom might well 
 have been a factor in the formation of these deposits. 
 
 Distribution of the Gravels. The facts connected with 
 these beds are as follows : Gravels of greater or less 
 thickness are present in almost all the principal 
 valleys, in a great number of the side tributaries, 
 and especially near points where longitudinal and 
 transverse depressions cross one another. Thus Wadi 
 Isleh emerges into the Ga'a plain between gravel cliffs 
 40 metres high, the pebble beds also extending for many 
 kilometres over the plain in the direction of Tor. 
 Another striking case is seen where Wadi Abuksheib 
 issues from the Ferani range, while a ridge partly bars 
 Wadi Kyd, a little south of its junction with Wadi 
 Melhadge. 
 
 Age of the Gravels. The age of the gravels is best 
 determined on the coast of the Gulf of Akaba, where they 
 are found to overlie raised coral-reefs at Ras Atantur, while 
 pieces of granite and schist are themselves mixed with and 
 cemented in between the Astrean corals, which are accom- 
 panied by such typical Pleistocene or recent forms as 
 Laganum depression, Heterocentrotus mammilatus, and 
 Tridacna. The gravels at this point are therefore not 
 earlier than Pleistocene, a conclusion quite in accord with 
 the results obtained for similar beds on the western side 
 of the Red Sea. 
 
 Character of the Gravels. The gravels above 
 mentioned are characterised by the fact that they 
 contain fragments of all shapes and sizes, derived 
 from the surrounding hills, which are embedded in 
 a sandy matrix consisting of material of the same 
 
The Geology of Eastern Sinai. 23 
 
 derivation, the source being thus strictly local. With 
 regard to the question of their origin, it is only possible to 
 suggest considerations, the theory which commends itself 
 to the writer involving a combination of two circum- 
 stances, viz., the earth-movements of which the region 
 shows such abundant evidence, and a greater rainfall. 
 
 The earth-movements might very readily have resulted 
 in temporary ponding back of the mountain torrents, when 
 it is recalled that the greater part of south-eastern Sinai is 
 even now almost a closed system, bounded on three sides 
 by mountainous watersheds, only one of which is broken 
 through by two valleys. With regard to the question of 
 greater rainfall, it need only be noted that at the present 
 day the storms, though frequent in winter, are of short 
 duration, and the resulting torrents are active in the work 
 of erosion, rather than of deposition, these being chiefly 
 engaged in rilling the smaller valleys with confused masses 
 of huge boulders, such as will be familiar to every traveller 
 who has climbed the mountains of the peninsula. 
 
 But one of the most striking features connected with 
 these gravel plateaux, is the perfectly flat nature of their 
 upper surface, even in the upland wadies, a character quite 
 inconsistent with their having been produced by rushing 
 torrents, but in accordance with the hypothesis of their 
 formation in ponded-back lakes, or marine fjords. The 
 apparent absence of any marine shells renders it probable 
 that the detrital beds of the central portion of Sinai are 
 due to deposition of the material derived from the 
 surrounding hills in lakes, rather than to their accumula- 
 tion in arms of the sea. Whatever theory may finally 
 gain acceptance must take account of their extensive 
 distribution, and the height at which they are now found, 
 they sometimes being 1200 metres above sea-level. 
 
24 The Geology of Eastern Sinai, 
 
 \b. MANGANIFEROUS PEBBLE GRAVELS. 
 
 While the majority of the bays of the Akaba coast are 
 broad inlets of the sea, running into the land between the 
 yellowish-white limestone cliffs of the raised coral series, 
 Sherm is at once distinguished by the red and black 
 colouring of the scarp commanding the bay to the west 
 and south. This exceptional appearance is due to the 
 presence of a conglomerate, whose constituents are 
 cemented by the hydrous black oxide of manganese, 
 psilomelane, in places as much as four metres thick, while 
 underneath are beds coloured red by ferruginous ochre. 
 These gravels are closely connected with a core of red 
 granite, stopping abruptly where the latter is no longer 
 exposed at the surface to the north, with the result that 
 the northern cliff is of a totally different character, con- 
 sisting of coral-reef, forming a cap to sand-rock of varied 
 tints. The manganiferous gravels, too, only seem to be 
 connected with and overlie the granite at the point where 
 the latter faces the sea, extending but a short distance up 
 the valleys, and not being found south of the transverse 
 chain of Zafara. It is interesting to note that the 
 Austrian ss. Pola found manganiferous deposits forming 
 on the floor of the Gulf of Akaba itself, a fact which lends 
 support to the view that these gravels are of marine origin, 
 though no organic remains have been noted in them. 
 
 \c. OOLITIC VALLEY DEPOSITS. 
 
 Walther, J. (' Die Korallenriffe der Sinaihalbinsel,' Bd. 
 xiv. ; AbhandL math. phys. Konigl. Sachs. Gesellschaft 
 der Wissenchaften, pp. 481-484), calls attention to the 
 fact, that near Suez, and especially on the border of the 
 
The Geology of Eastern Sinai. 25 
 
 Tyh desert, he found oolitic grains, while he had nowhere 
 noted oolitic rocks, either in Sinai or in the Arabian 
 Desert. From his examination he concludes that these 
 grains, met with especially at the mouth of Wadi Dehese, 
 are really a recent formation in statu nascendi. A closer 
 examination showed him that these consisted of quartz- 
 grains enclosed in a calcareous layer, and that when several 
 zones were present, there was a darker band between the 
 inner dark yellow, and outer clear shell of calcits. 
 Amongst the minerals noted as nuclei, were felspar, 
 garnet, magnetite, and fragments of Foraminifera. His 
 conclusion is that the mineral grains come from the desert, 
 and have been carried by land-winds into the shallow sea, 
 where various small animals would play their part in 
 assisting the formation of the calcareous coatings. 
 
 These interesting observations can now be extended, 
 as an oolitic rock of this very nature is most extensively 
 developed among the hills north of Ras Muhammed, 
 where it forms a striking light-coloured calcareous sand- 
 rock, bounding Wadi Hashubi, and almost filling the small 
 tributary valleys, which are reduced in many cases to 
 narrow canon-like ravines. Walther has mapped this as 
 Dtinensandstein of Hashubi. 
 
 The facts noted in connection with it are : 
 
 1. The sand-rock consists of quartz and orthoclase 
 grains, similar to those of the wind-blown sand in the 
 neighbourhood, cemented by carbonate of lime, which in 
 many places surrounds them in a series of concentric 
 coats. 
 
 2. These strata dip in every direction being often 
 plastered against the sides of the hills, or forming horizontal 
 beds cut down vertically in the gullies. In places they 
 show traces of ripple-marking, very fine sun-cracks, and 
 abundant longr tubular cavities. 
 
26 The Geology of Eastern Sinai. 
 
 In the lower part of Wadi Hashubi they are very thick 
 and horizontal, in some places being strongly current- 
 bedded and containing lenticular masses of pebbles, the 
 dip they show when overlying the surface of the igneous 
 rock being probably due to slipping of once horizontal 
 beds worn away from below, for the sand -rock has a 
 peculiar habit of weathering internally, a thin external 
 wall pierced by small holes only masking a larger internal 
 cavity. 
 
 Similar strata were found to be present in the small 
 side valleys of the lower igneous ranges west of Sherm, 
 but detrital material is more abundant than in Hashubi, 
 pebbles of granite over 10 cm. in diameter being present. 
 An interesting feature here too is the height at which the 
 sand-rock occurs, a typical example on the pass between 
 Jebels Abuzag and Hedemia being at 696 metres above 
 sea-level. 
 
 At the head of the valley running from this point the 
 canon structure is strikingly displayed, these light-coloured 
 beds forming almost vertical battlemented walls about 45 
 metres high (pierced with holes, mostly of semi-circular 
 form), overhanging a sandy plateau, which is again cut 
 into by narrow, winding ravines, themselves carried down 
 deeply in the underlying granite. 
 
 The origin of this remarkable deposit is again wrapped 
 in some obscurity, the natural view that it is of marine 
 derivation not being absolutely confirmed by the discovery 
 of any marine organisms. Nevertheless, the results ob- 
 tained by Walther are in favour of this hypothesis, which 
 would demand a differential movement of no less than 700 
 metres in the southern end of the peninsula during 
 comparatively recent times, a result which, though 
 startling, is in accord with evidence from neighbouring 
 regions. 
 
The Geology of Eastern Sinai. 27 
 
 id. GRAVELS CEMENTED BY CALCITE. 
 
 As though the difficulties connected with the superficial 
 deposits were not sufficient, there occur in the lower part 
 of Wadi Nasb, and especially close to its junction with 
 Wadi Abuksheib, certain terraces resting on Nubian sand- 
 stone and granite, containing boulders of syenite, biotite- 
 gneiss, felsite, and red granite (often over one metre in 
 diameter), cemented together by crystalline calcite in the form 
 of well-developed scalenohedral crystals. The question of 
 the source of the calcite which has acted as the cementing 
 substance rises. in connection with other beds which appear 
 in most unexpected places, viz. : 
 
 \e. TRAVERTINE AND CONGLOMERATE CEMENTED 
 BY TRAVERTINE. 
 
 The igneous hills are probably the last place in which 
 one would expect to find deposits of the above character, 
 but, subsequent to the first discovery by Mr. Skill of typical 
 calcareous travertine of spongy texture lining the walls of 
 a granite gully, or couloir, we frequently met with it in 
 out-of-the-way valleys, either in similar positions or at the 
 foot of precipitous steps, which would be waterfalls in 
 time of rain. In the latter cases a conglomerate of 
 igneous pebbles has been produced, the cementing sub- 
 stance being compact carbonate of lime, while in a fine 
 example occurring at the water-hole in Wadi Um Shokeh, 
 over 500 metres above sea-level, remains of the con- 
 glomerate cling to the walls of the ravine at the upper 
 level of the slope. From whence then would the calcite 
 be forthcoming for the formation of these beds ? Three 
 possible sources at once suggest themselves: (i) Cretaceous 
 
28 The Geology of Eastern Sinai. 
 
 limestones have been let down in Wadi Raib and are 
 abundant at its head, so that the torrents might bring 
 down bicarbonate in solution. (2) There is, however, no 
 evidence of the presence of these limestones in many 
 places where travertine is of common occurrence, so we 
 are driven to a second local cause, viz., the production of 
 calcite by the decomposition of the felspathic portion of 
 the diabase dykes. How far this is active can only be 
 proved by an analysis of selected torrent waters, a work 
 which must be undertaken by future travellers. (3) There 
 is, finally, the possibility already suggested that there has 
 been a marine depression to the extent of 700 metres, 
 which would probably bring all the valleys in which 
 travertine has been noted beneath sea-level. If this were 
 so, no further search need be made for the source of the 
 carbonate of lime. 
 
 SUMMARY. 
 
 It will thus be seen that the gravels, &c., suggest 
 considerable changes of level and different con- 
 ditions from those now prevailing, erosion at present 
 exceeding deposition. The theoretical deductions 
 helping to explain their presence may be here briefly 
 recalled : 
 
 1. In South-eastern Sinai earth-movements have pro- 
 duced three high watershed lines, only one of which is 
 now broken through. If these were formed at the same 
 period, all the water draining into the basin enclosed by 
 them would collect to form narrow lakes. This would 
 account for : 
 
 (a) The flat character of the plateaux. 
 () The absence of marine organisms. 
 
 2. A marine depression resulting in the invasion of the 
 
The Geology of Eastern Sinai. 29 
 
 sea, and amounting to at least 700 metres, is also suggested, 
 and would best account for : 
 
 (c) The oolitic beds of Wadi Hashubi. 
 (d} The manganiferous gravels of Sherm. 
 (e) The travertines of the higher valleys. 
 (/) The gravels of Nasb, cemented by calcite. 
 
 The flat character of the plateaux is also not excluded by 
 this hypothesis. 
 
 3. A subsequent elevation accompanied by earth-move- 
 ments, resulting in the uptilting of coral-reefs, brought the 
 formation 'of these special features to a close, the gravels 
 from the hills . being now distributed irregularly over the 
 surface, in places overlying the oolite beds, and being inter- 
 bedded with Pleistocene coral reefs. 
 
 II. 
 CORAL REEFS AND RAISED BEACHES. 
 
 At the commencement of the above-mentioned paper 
 of Professor Walther (loc. cit., p. 440) occurs the following 
 statement : ' The shore boundary rich in corals is entirely 
 wanting in the Gulf of Akaba. Only to the east of Ras 
 Muhammed small fringing reefs (Schirmriffe) are found 
 against the steep slopes of the cliffs, and more extended 
 reefs of younger Tertiary age are also to be observed. In 
 the main gulf there are also small coral aggregations at 
 the mouth of Wadi Nasb and Wadi Ghasaleh. Im- 
 mediately beyond the shore, depths of 60-150 fathoms 
 have been noted, while at the exit of the Tiran Straits, 
 bottom was only touched at 594 fathoms. Therefore the 
 
30 The Geology of Eastern Sinai. 
 
 Gulf of Akaba presents itself as a deep rift, bounded by 
 steep slopes, and poor in reefs/ 
 
 Somewhat of the same impression for the southern end 
 is left by a study of Moresby's Admiralty chart, which was 
 probably followed by Professor Walther, who does not 
 appear to have visited the Gulf of Akaba himself. As a 
 result of the present expedition, the above-expressed view 
 must be abandoned, Mr. Skill having now mapped con- 
 tinuous reef from Dahab to Ras Muhammed wherever it 
 was possible to get a view of the shore line, it forming an 
 almost unbroken fringe, which renders approach to the 
 coast dangerous for even small boats, except at a few 
 localities, such as Sherm, Dahab, and Nebk. 
 
 THE FRINGING REEF AND LOWER CORAL 
 SERIES. 
 
 The Fringing Reef is in reality one of the most con- 
 spicuous features of the gulf, extending from the shore as 
 a white, narrow, usually submarine, ledge, its outer border 
 being marked by a long line of surf, beyond which the 
 water is of intense dark blue colour, due to its great 
 depths. Closely associated with it, but at a higher level, is 
 a second reef, which to the north forms isolated terraces 
 up to 25 metres high, standing only a little way back from 
 the water's edge. The former is naturally the one which 
 attracts the attention of the zoologist, but the latter is also 
 characterised by a very rich and varied fauna. North of 
 Nebk this ' Lower Coral Series ' is only conspicuous at 
 three points : 
 
 1. The northern end of Dahab peninsula. 
 
 2. In one of the mountain bays to the south of Dahab, 
 and 
 
 3. Forming the point of Ras Atantur, at the northern 
 end of the sea-plain. 
 
The Geology of Eastern Sinai. 3 1 
 
 South of Nebk the terraces increase in thickness and 
 height above sea-level, and extend with but few breaks to 
 the neighbourhood of Ras Muhammed. The age of this 
 series presents no difficulty, as the limestone is crowded in 
 its lower part with such typical Pleistocene forms as the 
 flattened spines of Heterocentrotus mammilatus, Laganum 
 depressum, also Tridacna, Nidlipores, &c., Cceloria, and 
 Fungia. At both Dahab and Ras Atantur the uppermost 
 layer is a compact limestone, consisting of closely aggre- 
 gated Astraean corals, but in the former case the base- 
 rock is composed of granitic gravels, which near the 
 junction are full of large boulders of the igneous rock, 
 while at the latter locality the limestones rest on soft salty 
 marls, containing a band of broken oysters. 
 
 South of Nebk the contained fauna vies in richness 
 with that obtained on the western shores of the Red Sea, 
 where beds of identical age yielded several hundred 
 species. An especial point is the abundance and size of 
 the Gasteropoda, including a characteristic striped Strombus 
 (S.fasciatus) and large Terebras. 
 
 Raised Beaches. Closely associated with the lime- 
 stones of the ' Lower Coral Series ' are the Raised 
 Beaches which line the shore wherever the cliffs do 
 not rise directly from the sea. Many of the shells 
 are identical with those found in the neighbouring 
 terraces, while where the coasts are rocky, shells of 
 large Pteroceras bryonia and Tridacna, associated with 
 many beautiful sea-urchins, are crowded amongst the 
 boulders. This is especially the case between Nebk and 
 Daha,b, where in addition a thin ledge of raised coral- 
 reef, flanking the coast, forms a flat natural road, which 
 was very useful when mapping the hills, here dipping 
 steeply towards the gulf. The summit of this raised reef 
 is formed of a pavement of smoothed and polished blocks 
 
32 The Geology of Eastern Sinai. 
 
 of gneiss and hornblende-rock cemented together by white 
 calcareous material and corals, the whole forming a smooth 
 surface, which is an admirable track wherever developed. 
 This raised reef containing Astraean corals in abundance 
 may be equally included in the ' Lower Coral Series.' 
 
 UPPER CORAL LIMESTONE OR OLDER FOSSIL 
 REEF OF WALTHER. 
 
 South of Nebk a second coral reef flanks and apparently 
 overlies the lower one, but is evidently of older date, the 
 coral having undergone much alteration. This is the 
 same rock as the one described by Walther (loc. cit., p. 
 494), and of which he has given a very good figure when 
 representing the probable relations of the beds in his 
 No. 5, fig. 20, p. 465. 
 
 The characteristics of this bed are its extremely porous 
 nature, recalling in this respect the cavernous character of 
 a modern reef, but with this difference, that in the older 
 reef the cavities are filled up to a certain extent with 
 shells and broken calcareous fragments. It differs, too, 
 from the younger reef in its peculiar dirty-brown colour, 
 due in the main to the dolomitic alteration which has 
 been so frequently noted in connection with raised coral. 
 
 Owing to its perfect horizontality, a flat plateau has 
 been produced which extends a long distance between the 
 sea and the plain north of Sherm, unbroken by the 
 slightest elevation. South of Sherm it is less conspicuous, 
 though, as will be seen when the geological map near 
 Ras Muhammed is published, by no means uncommon, 
 and finally at the cape itself it attains a maximum height 
 of 90 metres, this being at a very different level from that 
 on the Gulf of Suez, where Walther gives 230 metres as 
 its height at Jebel Hammam Musa, north of Tor. 
 
The Geology of Eastern Sinai. 33 
 
 At present it is not possible to give a very clear idea 
 of the fauna of these beds, but the corals, which are still 
 in many cases well preserved, at least externally, agree 
 closely with those described from the higher reefs on the 
 west coast of the Red Sea, and include not only typical 
 Astraean forms, but also abundant mceandroid specimens 
 here provisionally referred to Cceloria. The most im- 
 portant genus in this upper Coral Limestone is probably 
 Orbicella. 
 
 The best sections are those seen immediately north of 
 Sherm, and from these the following typical succession 
 may be given, beginning from above : 
 
 1. Cavernous Calcareous Limestone (Older Coral Reef) 
 which has undergone dolomitic alteration, containing 
 Orbicella, and three other Astraean types, Cceloria, Ana- 
 dara, large gasteropod casts, Nullipores. Thickness one 
 metre. 
 
 2. Coral and Millepore limestone, in places forming a 
 small vertical cliff, and to the east changing into a 
 compact white chalk, in which are casts of large bivalves, 
 
 Venus reticulata. Four metres. 
 
 3. Oyster and Pecten bed, full of oysters, Pecten, 
 Laganum depressum, the small Echinus verruculatus, only 
 previously recorded from Mauritius (according to Professor 
 Gregory). 
 
 4. Brown and greenish salty marls. 
 These are apparently succeeded by 
 
 5. Nullipore rock. 
 
 6. Limestone with large ornate Venus, Cyprcea, Tri- 
 dacna, and a large Trochus. 
 
 7. Limestone rich in Gasteropoda, &c., including the 
 striped Strombus, Conus, Dentalium, sea-urchin spines (He- 
 terocentrotus}, Goniastrcea, and several species of Fungia. 
 
 8. This limestone is separated from the sea-shore by 
 
 C 
 
3-j. The Geology of Eastern Sinai. 
 
 two beaches, the higher consisting of larger spineless 
 specimens of Echinometra lucunter, associated with 
 Haliotis, while the lower consists of small varieties of 
 the same sea-urchin still covered with their spines. 
 
 Nos. I to 4 include the Older Coral Reef series, the 
 latter being the oldest member and No. I the youngest. 
 
 Nos. 5 to 7 form a second terrace, and compose the 
 Younger Coral Reef series, No. 7 being younger than 
 No. I, but older than 6 and 7. Finally No. 8 is quite 
 recent. 
 
 South of Aad Bay a still older set of beds make their 
 appearance, which differ from those previously described in 
 being tilted at high angles, in most cases standing well 
 back from the sea, and having undergone extreme altera- 
 tion. South-west of Aad Bay they form a small, but 
 conspicuous hill, rising 52 metres above the Upper Terrace 
 (that of the older Coral Reef) in which the beds of semi- 
 crystalline limestone are dipping 4 south-east and still 
 show traces of coral. South of Jebel Zafara, a conspicuous 
 east and west ridge near Sherm (well shown in a photo- 
 graph taken by Professor Natterer of the Polo], these 
 are still better developed, forming a series of yellow hills 
 lying close to the junction with the igneous rocks, and 
 rising nearly 200 metres above the sea. Here the beds 
 have been tilted to an extraordinary extent, in some cases 
 dipping from 30 to 60 east, and being apparently 
 connected with a longitudinal fault of importance. In 
 these the whole general appearance recalls the altered 
 coral reefs, and they still contain oysters and casts of 
 Pecten, but at present the evidence is not sufficient to 
 establish whether they are Pleistocene, or pre-Pleisto- 
 cene in age, a point obviously important in connection 
 with the discussion of the earth-movements in this 
 region. 
 
TJie Geology of Eastern Sinai. 35 
 
 Having thus dealt with such details as are necessary, 
 special stress may be laid on the following general 
 points : 
 
 The coral reefs of the Gulf of Akaba show the following 
 distribution : South of Aad Bay and Sherm there are 
 conspicuous tilted coral hills, and two horizontal terraces 
 representing Pleistocene reefs of different age. Going 
 north, between Nebk and Aad Bay, the two latter alone are 
 represented, the tilted beds being absent. Finally, north 
 of Nebk, only the Lower Terrace, or Younger Coral Reef, 
 and the recent fringing reefs are observed, there being no 
 trace of raised coral beds high on the sides of the hills such 
 as have been noted on the Red Sea coast. In other words, 
 the Older Reefs are only present at the southern end of the 
 Gulf of Akaba. 
 
 Coral Reefs formed in a region of elevation. From 
 what has been said above, it is obvious that only one 
 conclusion can be arrived at, viz., that the coral reefs 
 of the whole of this region have been formed during 
 a movement of elevation, the oldest ones being at the same 
 time tJie highest, while the upper terrace is composed of 
 beds which are older than those forming the lower terrace. 
 This elevation is directly proved from the present height 
 of the coral reef to be at least 200 metres in amount, and 
 the question arises, is it still being continued ? For the 
 Gulf of Akaba, the answer is perhaps a slight negative, the 
 chief grounds for this conclusion being the discovery made 
 by Walther, that a reef, probably dead judging from its 
 striking white colour, exists under the present submarine 
 living one, suggesting a local depression of about 6 metres, 
 and the same idea occurred to me as an explanation of the 
 fact that so many inlets from the gulf are only intrusions 
 of the sea up the mouths of the valleys. 
 
 Thus Ghazlani, Sherm, Aad, and Nasb Bays are all of 
 
36 The Geology of Eastern Sinai. 
 
 this nature. The only other alternative would be that the 
 material brought down by rains from the hills had had an 
 unfavourable effect on the growth of the reefs ; but against 
 this theory many objections can be urged. It therefore 
 appears probable that a small local depression (6 metres 
 according to Walther) is at present taking place in the 
 Gulf of Akaba, the latter differing in this respect from 
 neighbouring regions. 
 
 It will now be of general interest to take up the five 
 questions which Walther set himself, and see how far the 
 Gulf of Akaba leads us to agree with or differ from his 
 conclusions. 
 
 1. To what thickness may coral reefs attain ? In this 
 respect our agreement with Professor Walther is absolute, 
 
 .-viz., that a coral reef does not attain any great thickness. 
 Thus to the north of Sherm a bed mainly composed of 
 corals just exceeds I metre in thickness, and if the under- 
 lying limestones, Pecten beds, &c. be taken into account, 
 6 metres is the maximum noted. Presumably, Walther 
 has included these beds also when he gives the thickness 
 of the younger reef at Ras Muhammed as 9 metres, and 
 the older at about 7 metres, while the recent reef does 
 not exceed 3 metres. The greatest thickness of raised 
 limestone observed on the gulf is 54 metres, viz., in 
 the section described on page 14, yet an examination 
 of the component rocks will show that in all these beds 
 true coral reefs are of comparatively rare occurrence, 
 strata composed of millepores, calcareous algae, and 
 broken fragments of sea-urchins, mixed with innumerable 
 gasteropoda, being more conspicuous elements. 
 
 2. What is the basis of a coral reef? On this point our 
 results differ to a certain extent, and especially in one 
 particular to be referred to later. The upraised reefs give 
 good opportunities in many cases for a close study of the 
 
The Geology of Eastern Sinai, 37 
 
 base on which rests the limestone of the coral series, and 
 it is seen that the latter varies very widely at different 
 localities. Thus, at Dahab, it consists of granite gravels, 
 which near the junction are full of large boulders of the 
 igneous rocks, while at Atantur only soft, salty marls are 
 visible beneath the coral limestone. From Dahab to 
 Atantur no base rock has been observed, but the reef 
 projects directly from the hills composed of gneisses and 
 hornblende-granite, immediately outside which the sea 
 sinks to great depths, so that it is probable that the coral 
 has grown directly on the detrital materials derived from 
 the neighbouring mountains. Immediately north of 
 Sherm, a junction is again beautifully displayed, the coral 
 reef resting unconformably and horizontally on the 
 underlying sand rock (probably Nubian sandstone) which 
 here dips at four degrees, while elsewhere it overlies 
 gypseous sand-rock and marl. Again, near Hedemia 
 Bay, our field notes read, ' The road taken lay among the 
 coral-reef series, which forms a thin covering to sandy 
 beds with red ferruginous bands and lines of pebbles 
 dipping four degrees south-east, while in the small valleys 
 a flaggy rock of granitic materials also appears at the 
 base, having the same dip/ Walther, after a careful 
 discussion of the relations of the base to the coral reef 
 (loc. tit., pp. 496, 498), answers the above questions as / 
 follows : ' The fossil, and probably also the living coral 
 reefs of the Sinai peninsula are based on the outcrops 
 (Schichten-kopfen) of compact sedimentary [the italics are 
 ours] rock, they are wanting on the softer and more 
 crumbly coast-rocks of the Sinai peninsula.' The discus- 
 sion and conclusion both suggest that the igneous rocks 
 are of little use as bases for reef formation, but if this be 
 the right interpretation of Professor Walther's view, 
 strong exception must be taken here to such a limitation, 
 
38 The Geology of Eastern Sinai. 
 
 which would render it impossible to account for the 
 existence of the fringing reef bordering the hills south of 
 Dahab. Indeed, elsewhere, viz., on the western side of 
 the Red Sea, on the eastern border of Jebel Esh, where 
 coral-reef is tilted at over 20 all along the sides of the 
 igneous hills, the limestone is only separated from the 
 underlying granite by a thin granitic conglomerate, and 
 near Qosseir there is scarcely any detrital material 
 between the diabases and the coral bed plastered against 
 them. Instead, therefore, of having any limitation, we 
 conclude that, in general, the deposition of a coral reef is 
 practically independent of the nature of the rock forming its 
 base. Our own experience now includes red granite, 
 diabase, sand-rock, and marls, amongst the basal members, 
 with gneiss and hornblende-granite as highly probable. 
 
 3. What role does detrital filling material play in the 
 living reef? Practically, there is nothing to add to 
 Professor Walther's statements. He very justly points out 
 the easily breakable character of the madrepores and the 
 importance of the calcareous .algae, such as Lithotham- 
 nium and Lithophyllum in binding together the broken 
 fragments, or forming a crust over a sandy floor, on which 
 basis a coral reef can be built up. It may here merely be 
 further stated that attention is also called by the above 
 writer to the importance of crabs in breaking up the 
 organic remains, producing the fine calcareous sand, 
 which fills the cavities between the dying coral-stems, 
 and in addition may be noted the abundance of the red 
 encrusting foraminifer Polytrema, the fragments on the 
 shores of the gulf being in places completely overgrown 
 by this bright-coloured organism, 
 
 4. What alterations do the reef-sediments undergo 
 when they finally rise out of the water ? 
 
 The effects of change are only too quickly visible, the 
 
The Geology of Eastern Sinai. 39 
 
 brilliant-coloured living reef being replaced nearer the 
 shore by the dead-white surface so familiar to all students 
 of coral deposits. As the coral limestones are examined 
 the observer cannot fail to be struck with the absence of 
 many forms, which on the sea-shore itself seem to be the 
 principal members of the fauna. In vain will traces of 
 crabs be sought for, though on the beach they occur by 
 thousands, while the beautiful Phyllocanthus, the large 
 Heterocentrotus, and many other fine sea-urchins, are 
 only represented by spines in varying degrees of preser- 
 vation. Though Ophiurids fill every pool, they leave no 
 record behind them, and if it were not for the abundance 
 of Mollusca and the Corals, but little would be left to 
 recall the life and movement of the tropical marine fauna. 
 
 No doubt this disappearance has in large measure to 
 do with the instability of the aragonite composing the 
 skeletons of many of the above-mentioned animals, while 
 in addition, in the higher parts of the reef, the progressive 
 formation of casts from shells of S trombus, &c, can be 
 watched in all its various stages. But this is not the 
 only change to which a coral reef is subject, and the 
 upper terrace has lost its whiteness and taken on a dusty 
 grey appearance, which is indicative of the further 
 chemical alteration, viz., the passage from limestone to 
 dolomite by the increase in magnesia. 
 
 This change is too well known to require further 
 pressing here, and Walther's analyses show how far it has 
 advanced in some of the reefs. As a result the coral 
 structure has become practically obliterated, and in the 
 older reefs, where the correct identification of the fossil 
 contents is of first importance, the collector finds only 
 unidentifiable casts, or at most the last traces of calices 
 and septa. 
 
 5. The final question What alteration in form and 
 
40 The Geology of Eastern Sinai. 
 
 extension of reefs has taken place in the course of geo- 
 logical history ? has been answered as far as possible 
 previously, but it may be here repeated, that apart from 
 the tilted limestones whose age still remains uncertain, the 
 two horizontal raised reefs do not appear to be older than 
 the Pleistocene, north of Nebk the Pleistocene terraces, 
 but little above sea-level, being alone present. 
 
 CRETACEOUS LIMESTONES AND NUBIAN 
 SANDSTONE. 
 
 As has already been stated, the older sedimentary 
 strata only appears in the northern part of the area under 
 discussion, but these in the neighbourhood of Ain El 
 Hudera give rise to very varied scenic effects. 
 
 The main divisions recognised beginning from above 
 are as follows : 
 
 1. Cretaceous limestones, of considerable thickness, 
 somewhat poor in fossils, forming the summit of th< 
 plateau of Gunneh, which terminates in a steep escarp- 
 ment facing southward, and they also play a similar part 
 in the various outliers let down in the rift valleys, as 
 described in the paper dealing with those occurrences. 
 
 2. Underneath the limestones a highly characteristic 
 striped series of green marls, &c., is always present, which 
 contains typical Cenomanian fossils, such as Hemiaster 
 cubicus, Pseudodiadema variolare, and Heterodiadema 
 libycum. 
 
 3. The marls themselves are only the surface capping 
 to a thick series of white sands, which, having been cut by 
 vertical furrows to their very base, now rise as isolated 
 masses over 100 metres high, bordered on all sides by 
 
The Geology of Eastern Sinai. 41 
 
 vertical walls, and, owing to the softness of the material, 
 far more dangerous to climb than the higher igneous 
 hills to the south. 
 
 4. These are based on broad, low, smooth plateaux, in 
 general dipping gently northward, due to a hard ferruginous 
 bed overlying variously coloured ferruginous sandstones, 
 which themselves have been deposited on a planed-down 
 surface of granite. 
 
 Owing to the existence of the Raib rift, these strata are 
 separated from the sea by the long range of granite which 
 runs from Noweiba to Dahab, and similarly granite hills 
 rise from amongst them, or tongue into them in an 
 apparently bewildering manner when first observed, though 
 after a time it is possible to trace the various faults and 
 folds which have caused the complexity. 
 
 One or two special examples will further illustrate 
 these points : On ascending the northern bend of Wadi 
 Nasb and Wadi Um Raiyig, which continues it to the 
 northward, the valley is suddenly narrowed by a tongue of 
 granite projecting from the eastern cliff, and only widens 
 out again behind it to be once more completely barred. 
 The nature of the obstruction is interesting, for while the 
 side wall of the valley consists of granite, on which rests 
 the flat-topped ferruginous sandstone (No. 4) above 
 mentioned, the barrier itself is of very different composition, 
 its base consisting of the fine white sand-rock (No. 3), im- 
 mediately succeeded by green and closely banded marls, 
 almost entirely consisting of oysters and mytiloid forms 
 (probably Ostrea africand). Above these follows a com- 
 pact limestone about 6 metres thick, crowded with casts of 
 a large Tylostoma-\\k. univalve, and in the downwash a 
 small variety of Hemiaster cubicus is abundant, also 
 Tylostoma and flat bivalves, and large forms of Cucullcea 
 are also found in the upper layers. 
 
42 The Geology of Eastern Sinai. 
 
 The total thickness of these striped beds is 18 metres, 
 the summit being formed of non-fossiliferous bedded lime- 
 stones. Practically every section of the striped series 
 examined in this region yielded these Tylostomas and 
 Hemiaster cubicus. Many local variations are, however, 
 noticeable ; thus, in an outlier north of Um Raiyig, small 
 red Nucleolites and Heterodiadema hbyciim occurred in 
 hundreds weathered out at one spot on the hill, and in 
 most of the exposures a large Exogyra bed is conspicuous 
 near their base. 
 
 The escarpment of Jebel Gunneh also gave a good 
 section for thickness, this being determined as follows : 
 
 Metres. 
 Compact limestones, from which the fossils are 
 
 difficult to obtain in recognisable form, pro- 
 visionally referred to Cenomanian ... ... 100 
 
 Marls and limestones with typical Cenomanian 
 fauna, including large Exogyra and Tylostoma, 
 Hemiaster cubicus, Heterodiadema libycum ... 20 
 
 White sands and ferruginous Nubian sandstone 207 
 
 Total thickness ... ... 327 
 
 Very briefly, then, the lessons suggested by the sedi- 
 mentary series at this point are as follows : 
 
 i . The granite was planed down and the Nubian sand- 
 stone deposited regularly on the plain of marine denuda- 
 tion. In this region there is no case of the dykes (so 
 abundant in the granite) passing up into the sandstone, 
 they being cut off abruptly at the point of junction. The 
 sandstone at the base, brightly-coloured, ferruginous, and 
 false-bedded, passes up into a great thickness of white, 
 friable sands, themselves underlying marls and limestones 
 
The Geology of Eastern Sinai. 43 
 
 containing a Cenomanian fauna which belongs to Zittel's 
 Africano-Syrian Series, since Mr. Beadnell's discovery of a 
 group of Cenomanian fossils in Baharia, shown to have 
 had an enormous extension north of latitude 28 north. 
 It will be seen from the above remarks that the 
 Carboniferous limestone has died out to the east, and there 
 is no proof whatever that any of the Ain el Hudera sand- 
 stone is Carboniferous, but, as in the whole 200 metres no 
 fossil has been obtained, no decisive answer can be given 
 on this point. Similarly the uppermost Cretaceous beds in 
 Jebbel Gunneh have not yielded a fauna capable of closer 
 identification. 
 
 Attention has been called in the first part of this paper 
 to the remarkable extension southward of the Cretaceous 
 limestones and Nubian sandstones owing to the faulting of 
 the peninsula, so that Exogyras of the Cenomanian series can 
 be collected in Wadi Raib from low hills, on both sides of 
 which rise steep walls of granite 500 metres high, while 
 similarly the Nubian sandstone of the Shelala Pass is 
 dominated by ranges whose summits are 600 metres above 
 the valley. 
 
 The history of South-eastern Sinai since and including 
 Cretaceous times thus presents many gaps, for records 
 from the Eocene and Miocene, and possibly Pliocene as 
 well, are absent, yet sufficient remains to show that during 
 the Cenomanian period began the depression first marked 
 by sandstones and sandrock, and gradually succeeded by 
 the fossiliferous marls and limestones. 
 
 The dip and present position of the Nubian beds would 
 be sufficient to show that these strata once extended over 
 the whole of the present igneous mountain region, even if 
 they were not found let down in the heart of the moun- 
 tains, and flanking the plain between Nebk and Ras 
 Muhammed, where sandy layers, sometimes containing the 
 
44 -The Geology of Eastern Sinai. 
 
 quartzite pebbles typical of the Nubian, form the basis of 
 the superincumbent coral reefs, Only with the Pliocene or 
 Pleistocene is the record once more resumed, but no longer 
 as a story of quiet depression and deposition, but one of 
 storm and stress, of mountain upheaval and gigantic frac- 
 ture, producing valleys cutting deep into the plateaux, and 
 giving rise to a topographical puzzle, which we hope partly 
 to have elucidated, and which will be more clearly under- 
 stood when the map prepared by Mr. Skill shall have been 
 published, geologically coloured along the lines of our 
 original field-sheets. 
 
 Resulting from these movements the Gulf of Akaba 
 came into existence, and connection was set up with the 
 Indian Ocean by way of the Red Sea, the depressions and 
 elevations produced being witnessed to by the coral reefs 
 and gravels described in the previous pages. 
 
 ADDITIONAL NOTES. 
 
 THE IGNEOUS ROCKS OF EASTERN SINAI. 
 
 The Peninsula of Sinai has been justly described by 
 Captain H. S. Palmer, as follows : (' Ordnance Survey of 
 Peninsula of Sinai/ Part I, Chapter I, page 17). 'The 
 Peninsula of Sinai, or at any rate the greater part of it, 
 is in reality one of the most mountainous and intricate 
 regions on the face of the earth : sand is a feature seldom 
 met with, plains are rather the exception than the rule, 
 the roads are often steep and rugged, and wind for the 
 most part through a labyrinth of narrow rock-bound 
 valleys. It is a desert, certainly, in the fullest sense of 
 the word, but a desert of rock, gravel, and boulder, of 
 
The Geology of Eastern Sinai. 45 
 
 gaunt peaks, dreary ridges, and arid valleys and plateaux, 
 the whole forming a scene of stern desolation which fully 
 merits its description as the "great and terrible wilder- 
 ness." So far from there being nothing to survey, the 
 topographer may well shrink from the task of delineating 
 its countless intricacies.' These words are no exaggeration, 
 and a few figures tell the same tale, for during a period 
 of seven months, Mr. Skill and the writer ascended over 
 54,000 metres in the course of the daily work (this 
 excluding all minor stations), the average height of the 
 summits ascended for over four months and a half being 
 450 metres per day. 
 
 In addition to the mere surface diversity, the geological 
 structure plays a great part in producing scenic variation, 
 granite ranges rising in abrupt precipice or smooth-sided 
 slopes above deep ravines, and breaking up into sharp 
 peaks or thin saw-like crests. Elsewhere, as in the Ferani 
 range, felsites have produced high plateaux, only slightly 
 undulating at the summit, but terminating on all sides in 
 frowning cliffs, which tower above rock-strewn and sinuous 
 boulder valleys, during times of storm scoured by rushing 
 torrents and foaming cascades. Standing on the central 
 summit of Abu Mesud and looking towards the Gulf of 
 Akaba, the eye rests on a dark confused mass of hills 
 mainly composed of schists contrasting strongly with the 
 granite which surrounds them on every side, one of the 
 most arid regions in the whole peninsula barren ridges 
 dominating sinuous gorges, where only a scanty herbage 
 finds a foothold. 
 
 THE IMPORTANCE OF DYKES AS DETERMINING 
 SCENERY, &c. The traveller in Sinai, and especially 
 one who has to examine it closely, is almost immediately 
 struck with the remarkable banding of the whole country 
 by variously coloured dykes, which seam the mountains, 
 
46 The Geology of Eastern Sinai. 
 
 running over the highest peaks, and preserving a perfect 
 parallelism to each other, which persists over many kilo- 
 metres. Thus, even before Wadi Isleh is entered, the 
 small ridges which cluster at the foot of the higher 
 mountains are all seen to owe their origin to dykes 
 mainly running in a N.N.E. and S.S.W. direction, while 
 in the high ranges of Shiddok and Emlaha, the red and 
 dark bands pass over the main crest. Our own obser- 
 vations show that these veins practically extend throughout 
 the whole igneous region over many kilometres, without 
 any perceptible break in their continuity, and by their 
 superior hardness determine the directions of many ranges. 
 
 When composed of basic rocks, they often produce 
 gullies, which not infrequently form the only road by 
 which some of the steeper scarps can be ascended. 
 
 These dykes are of almost every petrographical 
 variety, from the coarse quartz-felsites and fine-grained 
 felsites, which are more commonly found in the granitic 
 regions, to the dark dolerites and spheroidal diabases 
 which, in the metamorphic districts, are sometimes so 
 crowded as to completely mask the schistose rocks 
 enclosed between them. They are clearly the youngest 
 members of the igneous series, as every other type of 
 rock has been penetrated by them, but as has been 
 previously remarked, none of them have been noted 
 passing into the Nubian Sandstone, which rests upon a 
 plane cutting them off abruptly. Thus, in Eastern Sinai, 
 at any rate, all the dykes appear to be Pre-Cenomanian, 
 and, judging from the neighbouring regions, probably 
 Pre- Carboniferous as well. 
 
 DUPLICATE SYSTEM OF DYKES. While the general 
 trend of the main system of dykes is N.N.E. and S.S.W., 
 there is frequently a second system, practically at right 
 angles, which in some cases shows marked differences, 
 
The Geology of Eastern Sinai. 47 
 
 though these are not sufficiently constant to establish 
 any general rule. Thus in the slopes of Abuksheib, 
 above Wadi Nasb, a N.W.-S.E. running group consists 
 of basic dykes which have shifted the acid and basic 
 members of the principal series, and is consequently of 
 younger age. At other times two cross each other, giving 
 rise to X-shaped forms such as are developed in Wadi 
 Letih, or to an interlacing mass of dark veins, there being 
 a beautiful example of this class in the hills near Dahab. 
 
 For further remarks see Holland, ' Ordnance Survey/ 
 p. 220, Fraas, and many other writers. 
 
 The dykes vary considerably in thickness, sometimes 
 being only a few centimetres wide, while more commonly 
 they vary from the ten metre bands of Isleh and Beidha 
 to the huge green dyke, 100 metres broad, which runs 
 steeply up the granite slope opposite Jebel Jeraimdeh, 
 near Dahab. 
 
 It is here only possible to mention in addition that 
 in the broadest outlines the Sinai Hills resemble the 
 mountains on the opposite side of the Red Sea, though the 
 fundamental rocks of the central axis of the peninsula 
 are granitoid gneiss and hornblende-granite, not the red 
 granite which forms the main summits in the Red Sea 
 Hills. The latter is, however, also widely distributed in 
 the peninsula, especially in its northern half, and in 
 places it has been found possible to map the line of 
 junction of the two types. Of special interest are beds 
 of andesite, tuff, and agglomerate, which form some of the 
 principal summits capping the granite and gneiss. This 
 ' Volcanic Series/ which recalls that of Jebel Dokhan, 
 crowns the' high ranges of Katherina, Abu Mesud, and 
 Ferani, and is in general only a surface covering underlaid 
 and intruded into by the granites, &c. Closely associated 
 with it is a MetamorpJiic type, developed in a broad 
 
48 The Geology of Eastern Sinai. 
 
 region embracing many of the lower hills near the Gulf 
 of Akaba between Dahab and Nebk, and giving rise to 
 a series of steep-sided ranges enclosing deep, barren, 
 desolate, and waterless valleys. On the west above Wadi 
 Kyd these rocks are mainly spotted slates, ' Knoten- 
 schiefer,' containing large quartz pebbles which have been 
 recemented, and compact yellowish-grey siliceous varieties. 
 Further to the east they are replaced by true dark -green 
 chlorite and hornblendic schists, pierced near the Gulf 
 of Akaba by innumerable dykes of dolerite, and flanked 
 towards the sea by a band of grey and red gneiss, 
 while nothing is more striking than the abrupt junction 
 between the granite and schists where the two meet in the 
 hills north of Nebk. 
 
 It is impossible here to discuss the numerous questions 
 connected with regional and contact metamorphism on 
 which Sinai may help to throw light, as there has been as 
 yet little opportunity to compare the results noted with 
 those recorded in the literature already collected on this 
 subject. Some of the most striking special features 
 observed are as follows : 
 
 (a) In Wadi Um Gerat, a short distance from the 
 junction of the granitoid gneiss and schists, true gneisses 
 are developed on a magnificent scale, occurring, however, 
 in bands only a few metres thick, alternating with a 
 finely developed deep-green or black hornblende-schist. 
 This highly foliated structure seems to be purely local, 
 the gneissose character being usually somewhat obscure, 
 though clearly marked on a smaller scale at many points, 
 e.g., in Wadi Isleh. 
 
 (b) In Wadi El Tema the junction of the granitoid 
 gneiss and schists is marked by a band of peculiar gneiss 
 which appears to be composed of the two members closely 
 interlaminated, suggesting that the granite has been forced 
 
The Geology of Eastern Sinai. 49 
 
 in a molten condition between the laminae of the schistose 
 rock. 
 
 (V) While the main summits of the southern range are 
 composed of a granite with little quartz, and much acicular 
 hornblende (almost a syenite), the spur of Haimar and 
 Jebel Aad consists mainly of a well marked tourmaline- 
 granite, whose precise relation to the first-named has not 
 been determined. 
 
 (d) The gneisses seem chiefly limited to the high 
 ranges, the low country to the south being mainly formed 
 of true granite rich in porphyritic felspars, while north of 
 Wadi Nasb the areas occupied by the two types are 
 sharply marked off from one another, differing in colour, 
 and to a certain extent in surface features as well. 
 Thus, the true granite country is usually more rugged, and 
 has a distinct and characteristic pink shade. 
 
 (e) Spherulitic Felsites are very abundant in the district, 
 and have been shown to form part of dykes penetrating 
 the granite, &c., and not to be members of an outpouring 
 of lava at the surface. 
 
 (/) No proof has been obtained of the existence of 
 basalt, such as was stated to be present near Sherm by 
 Burckhardt. The only black rock of any importance in 
 that neighbourhood is the manganiferous gravel previously 
 described. 
 
 In conclusion, it will be seen from these brief notes, 
 that the igneous and metamorphic rocks themselves afford 
 a wide field for speculation and study, and will be dealt 
 with more fully when sections have been made of the 
 specimens brought back for closer examination. 
 
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