Vol. 59.] THE SEMNA CATARACT OF THE NILE. f)5 



9. The Semna Cataract or Eapid of the Nile : a Study in River- 

 Ebosion. By John Ball, Ph.D., A.R.S.M., F.G.S., Assoc.M. 

 Inst.C.E. (Eead November 19th, 1902.) 



[Plates III & IV.] 



Contents. Page 



I. Introductory 65 



II. Topographical Description of the District , 66 



III. Geology 69 



I. Introductory. 



Of the numerous ancient inscriptions discovered in Egypt by 

 Lepsius during his expedition of 1812-1845, few were of a 

 higher degree of interest than those on the rocks at Semna, between 

 the Second and Third Cataracts of the Nile, which record the levels 

 of high Nile in various years under the 12th and 13th dynasties. 

 Eor, apart from their purely historical value as indicating the 

 importance attached, even at that early age, to precise records 

 of the river which has always been the life-stream of Egypt, these 

 marks serve as a means of gauging the local changes which have 

 taken place through the geological agency of river-erosion during a 

 period of about 4200 years. 



Lepsius spent 12 days at Semna and the neighbouring village of 

 Kumna, and besides copying a large number of the inscriptions and 

 making detailed plans of the two temples situated one on each side 

 of the river, he made a sketch-plan of the rapid, and determined 

 the fact that the high-Nile level indicated by the sculptured marks 

 on the rocks is about 24 feet higher than the high Nile of our own 

 day. The data published by Lepsius in his great work 1 were the 

 subject of a careful consideration from the geological standpoint by 

 a former president of the Geological Society, Horner, in 1850. 2 

 Horner, who does not appear to have himself visited the place, 

 came to the conclusion that 



' the only hypotheses that could meet the requirements of the facts observed, 

 would be either the wearing away of a reef or barrier at the place in question — 

 a process requiring too long a period — or the existence at some distant period 

 of a dam or barrier, formed perhaps by a landslip of the banks, at some narrow 

 gorge in the river's track below Semna, which in the course of time had again 

 been washed away : — but of the existence of any such contraction of the channel 

 where such a barrier was possible there is as yet no evidence The con- 

 ditions attending these markings, at present so enigmatical, offer an interesting 

 problem to any geologist, well versed in the questions of physical structure 

 involved, who may hereafter visit Nubia.' 



1 ' Denkmaler aus iEgypten&iEthiopien ' Leipzig, 1849-59, Abth. i, Bl. 111- 

 113 ; Abth. ii, Bl. 139 ; Abth. iii, Bl. 47-67. See also Lepsius's * Letters from 

 Egypt' p. 269. 



a Quart. Journ. Geol. Soc. vol. vi (1850) p. 384. The paper is only published 

 in abstract ; I have been unable to consult the original manuscript, so as to 

 examine Horner's reasoning more fully. 



Q. J. G. B. No. 233. f 



