Rocks in the Nile Valley, in Nubia. 131 



is also the lowest, and only 2*50 metres (8 feet 1 inch) above the highest 

 inundation ; the next in height is 2*70 metres (8 feet 9^ inches) above the 

 former, and was made 250 years earlier, under Tutmes III. Although I 

 only measured the present level of the valley near Korusko, nevertheless 

 it appears to me that, during the whole of the new kingdom, that is, from 

 about 1700 years before Christ to this time, the Nile has not reached to 

 the full height of the low land of the valley. 



** It is, however, conceivable that, at the time when the present low 

 land of the Nubian Valley was formed, the cataracts at Assuan were in a 

 totally diiferent state ; one that would, in some degree, justify the over- 

 charged descriptions of the ancients, according to whom they made so 

 great a noise that the dwellers near them became deaf. The damming up 

 of the inundation at Assuan could have no material influence on Egypt, 

 any more than that at Semne, or the land from thence to Assuan." 



It appears therefore, from the above statements, that at the time 

 mentioned, the Nile, during the inundations, stood 26 feet 8 inches 

 higher than the highest level to which it now rises in years of the 

 greatest floods ; and that, to account for this. Professor Lepsius con- 

 ceives that, between the time of Mcesis and the present day, the bed 

 of the Nile, from a considerable distance above Semne to Assuan, 

 must have been worn down to that extent. In the index to the 

 volume of the Berlin Monatsbericht, in which the letters of Profes- 

 sor Lepsius are inserted, there is the following line: — 



** Nil, senhung seines Bettes um 25 Fuss seit 4000 Jahren." 

 " Nile, sinking of its bed about 25 feet (Paris) within the last 4000 

 years." 



Rivers are, undoubtedly, among the most active agents of change 

 that are operating on the earth's surface ; the solid matter which 

 renders their waters turbid, and which they unceasingly carry to the 

 sea, afford indisputable proof of this agency. But the power of 

 rivers to abrade and wear down the rocks over which they flow, and 

 to form and deepen their own bed, depends upon a variety of cir- 

 cumstances not always taken into account ; and although the great 

 extent of that power, in both respects, is shewn in the case of many 

 rivers, to conclude, as some have done, from these instances, that all 

 rivers have excavated the channels in which they flow, is a gene- 

 ralization that cannot be safely assented to. The excavation of the 

 bed of a river is one of those problems in geological dynamics which 

 can only be rightly solved by each particular case being subjected to 

 the rigorous examination of the mathematician and the physicist. 

 The solid matter which rivers carry forward is in part only the pro- 

 duce of their own abrading power ; and the amount of it must be 

 proportional to that power, which is mainly dependent on their 

 velocity ; they are the recipients of the waste of the adjoining lands 

 by other combined agencies, and the carriers of it to the lower dis- 

 tricts and to the sea. They often affbrd the strongest evidence of 



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