THE DISINTEGRATION OF GRANITE IN EGYPT 393 



The massive granular disintegration of the Aswan region 

 possibly also may be attributed directly or indirectly to the effect 

 of moisture. The disintegration is found at and for some few 

 meters below the level at which the Nile must have flowed when 

 in the old Nile Valley between Aswan and Shellal. At that time 

 the granite at the level of this disintegration must have been 

 alternately above and below the ground-water level, as the Nile 

 rose and fell, and must consequently have been alternately wet 

 and dry. At the present level of the Nile, the granite was found 

 in the excavations for the navigation canal and for the dam founda- 

 tions to be almost completely disintegrated and decomposed to a 

 depth of several meters below the level of the high Nile. Decom- 

 position in this case has, however, rather predominated over simple 

 disintegration. 



These observations in the light which they throw on the cause 

 of the disintegration of granite are in agreement with similar 

 observations which the writer made in the Odenwald, in the Vosges 

 Mountains, in the Norvan and Auvergne districts of France, and 

 in the eastern United States. In the many places in which the 

 disintegration has reached the depth of 20, 30, or even 40 ft., it 

 seems impossible to believe that the temperature changes are of 

 sufficient amount to be of any appreciable effect. Diurnal, weekly, 

 and monthly temperature changes must be completely eliminated 

 at those depths, and according to Sir William Thompson the 

 annual temperature range is reduced at a depth of 25 ft. to one- 

 twentieth of its superficial amount. The disintegration in these 

 places is accompanied in many cases by very much more and in 

 other cases by only slightly more decomposition than is the dis- 

 integration in Egypt. 



