540 CAPT. H. G. LYONS ON THE STKATIGRAPHY AND [Nov. 1 894, 



influenced the course of the river at Korosko and at the Third 

 Cataract, while between these points it runs at right angles to the 

 direction of the folds ; it is also of interest to note the grouping of 

 the wells in the Eastern desert. Till that part is carefully examined 

 nothing of course can be said with certainty, but I would point out 

 that the prolongation of the Bir Murr-and-Korosko line falls on the 

 wells of Keriyat, Haimar, and Movia, with Derehit farther east, 

 and that the general direction of the valleys, especially the upper part 

 of the Wadi Allaki, is the same ; while the wells of Khattat, Om Rish, 

 Khosfur, Rept, Sufir, Medina Dilet-el-Dom and Murat, with that 

 of Shikr farther to the east, are on the Shebb-and-Wadi Haifa line. 



North of the area we have hitherto been considering, a series of 

 folds, having a general north-and-south direction, come in and are 

 well seen in the Kharga Oasis from the village of Bulak northwards, 

 where the strongest springs occur, as usual, situated along them. 

 In some cases ancient springs occur at heights of 60 to 80 feet 

 above the level of the plain, and in old times yielded an abundant 

 supply, but now are sanded up and closed through neglect, only 

 furnishing enough moisture for a few dom-palms which still grow 

 round them. 



At the Farafra Oasis the folds seem to be rather east of north, 

 judging from Zittel's map, and to pass through the Baharia Oasis, 

 5 miles north of which I saw most marked anticlinal folding of the 

 Upper Eocene limestone-beds. By the villages of Mandisha and 

 Zubbo, in the northern part of this latter oasis, there was distinct 

 faulting of the Cretaceous sandstone-beds, which have been brought 

 up till they form the floor of the oasis, and in them the springs 

 occur, the water-bearing rock being met with at a depth of about 

 90 feet from the surface, furnishing a most abundant supply. 



The Natron Lakes owe their water-supply, I believe, to a fault 

 along the line of the valley bringing up the water to form a line of 

 springs. These springs are, as a rule, fresh, and take up sodium 

 chloride from the surface-beds, but, after percolating slowly through a 

 reedy marsh with much decaying vegetation, water appears containing 

 sodium carbonate, which is deposited on evaporation of the lakes. 

 The springs in this valley, which is very little — if at all — above sea- 

 level in the neighbourhood of the lakes, are affected by the pressure 

 of the Nile water, and when that is in flood the water in the wells 

 rises slowly to a maximum of about 2 feet, as I was told, above its 

 lowest level. There are a few other places which require careful 

 examination in this connexion, to see whether any modification of 

 the views that I have put forward is necessary. Among these is 

 the Fayum, which was doubtless at one time an oasis like the 

 others, and was fed by springs which supported patches of vegetation 

 round them ; but now that the irrigation is done by Nile water, 

 brought in by the Bahr Jusef Canal, the influence of the springs 

 is masked by the river-water, and is seen only in the fresh- 

 water springs on the edge of Birket-el-Kurun and in the Wadi 

 Ray an. 



