384 DONALD C. BARTON 



have taken place under the estuarine or marine conditions then 

 prevailing or at some later time under the action of ground-water. 

 The disintegration and decomposition penetrate cracks to the 

 depths of 10 to 20 ft. and in one or two places may be seen to have 

 taken place before the disintegration next to be mentioned. 



The effects of the second period of disintegration are mani- 

 fested in a tendency toward deep, granular disintegration massively 

 affecting the coarse Syene red granite at a level which is approxi- 

 mately that of the Aswan Reservoir when full. This disintegration 

 is best seen on the island of El Hesa, in some recently excavated 

 graves at the site of the former village of Garba. The graves are 

 cut back into hill slopes of various inclination and have a hori- 

 zontal depth of about 3 meters on the average and a height of about 

 1 j m. The roof at the back commonly has a thickness of 1 to 2 m. 

 The greatest distance to which a grave was seen to extend hori- 

 zontally backward from the surface of the hill slope was 4 m. 

 The height of the grave was about if m. and the roof at the back 

 was slightly over 2 m. in thickness. The graves are cut entirely 

 in the disintegrated, or rather, partially disintegrated, granite 

 and in no case were they seen to penetrate unaffected rock. The 

 disintegration has therefore penetrated to a depth of at least 3 to 4 

 meters from the surface. The disintegration is of the granular 

 type and, although affecting the rock uniformly, is not quite com- 

 plete; blocks of the granite may be obtained which to the eye 

 seem entirely sound but which crumble readily under the hammer. 

 In the shallow sections that are afforded there is not any appreci- 

 able decrease of intensity of the disintegration with depth. The 

 disintegration has been accompanied by slight but megascopically 

 noticeable kaolinization and in its products resembles closely the 

 partial granular disintegration which is found at a depth of about 

 4 m. in the Morvan and Plateau Central regions of Central France. 

 This tendency toward massive granular disintegration is mani- 

 fested also at several points along the old Nile Valley about 1 km. 

 north-northeast of Shellal, at several points along the river trail 

 from Shellal to the Aswan Dam, at several points immediately 

 north of the village of Kuror along the river trail to Aswan, and 

 about one-half mile northeast of Kuror in a small pass on the trail 



