THE GEOLOGY OF EGYPT. 397 



The geological formations which are represented in 

 Egypt are not very numerous. For convenience of de- 

 scription they may be grouped as follows : — 



Crystalline and schistose rocks. 



Nubian Sandstone. 



Cretaceous. 



Eocene and Oli^ocene. 



Miocene. 



Pliocene and recent. 



Crystalline and schistose rocks.- -The crystalline and 

 schistose rocks which form the basis upon which rest the 

 sedimentary formations of Egypt, are first exposed in the 

 bed of the Nile near the First Cataract at Assuan. Many 

 writers have referred to them more or less briefly, but 

 they have never been very carefully examined. Hawkshaw 

 (13) has given a map of the area, and Dawson (9) has 

 divided the rocks into two series which he correlates with 

 the Laurentian and Arvonian ; while Bonney (6) and Miss 

 Raisin (21) have described their penological characters. 

 Dykes of diorite appear to be abundant. 



According to Floyer (10) the crystalline rocks which 

 form the core of the range of mountains along the shores 

 of the Red Sea, have metamorphosed the sandstone in 

 contact with them f and according to Johnson (15) there 

 is a similar alteration around the granite near Kalabsheh, 

 above Assuan. Much doubt has been cast on these 

 statements ; but it should be remembered that most large 

 crystalline masses consist of rocks of various ages, and 

 some of these are usually intrusive. Moreover, the "sand- 

 stone ' : which is in contact with the crystalline rocks is 

 probably not everywhere the same age. Some of it is 

 almost certainly Palaeozoic and some of it Cretaceous. 



Nubian Sandstone. — The " Nubian Sandstone," as the 

 term is generally used in Egypt, includes the whole of the 

 beds which lie between the crystalline rocks and the fossil- 

 iferous Cretaceous series. At Assuan it rests upon gneiss 

 and schist ; but a little west of the Nile it extends much 

 further south, and occupies in fact nearly the whole 



