OF EGYPT. 31 



this probably accounts for the great absence of lamination in 

 the alluvium; for the successive deposits would naturally- 

 become mixed by cultivation, the boring of insects, and the 

 natural cracking of the mud as it dries, together with the 

 drifting of the particles by the wind. 



We know that the sea once washed the foot of the rocks on 

 which the Pyramids of Sakkara stand, the bases of which are 

 now bathed by the inundations of the Nile from seventy to 

 eighty feet above the Mediterranean ; but when we attempt to 

 carry back our ideas to such a remote period, we are lost in 

 the contemplation of so vast an interval of time during which 

 the Nile has deposited the hundred square miles of soil which 

 now form its true Delta. Besides the great volume of allu- 

 vium brought down from the river- sources, there is vast 

 degradation taking place along its course ; for the atmosphere 

 acts very considerably in crumbling the sandstone ; and the 

 wind, carrying these particles along, adds to the Nile-deposit, 

 forming sandbanks in the river, which are now added to and 

 then swept away again by some slight alteration in the 

 currents; and, owing to the power of the wind to drift sand, 

 the physical aspect of Nubia is constantly changing. This is 

 probably the great source from which the sandy particles in 

 the Nile-deposit are derived, while the clayey portions are 

 mostly brought down from Abyssinia. In Nubia we can 

 trace the effects of the tremendous scouring which the country 

 has undergone, at one time or another, in the torrent-beds 

 and deep valleys of denudation which are cut through the 

 horizoutal strata. The heavy storms which occasionally break 

 over the country bear a large amount of strata into the 

 river. 



The Nile, like other rivers, has often shifted its course, as 



