or EGYPT. 37 



lies in the great rent in the limestone formation hollowed out 

 by the Nile waters, and which averages, from Cairo to Assouan, 

 five or six miles in breadth. Such is the wealthy laud of 

 Egypt ; for the desert is only a home for the Gazelle and the 

 Vulture. 



4. Crystalline rocks. — These are not met with until we 

 reach Assouan ; but there they are seen in vast masses 

 hemming in the river on all sides at the First Cataract. 

 Here the scenery changes from the fruitful land of fertile 

 Egypt into the bleak and barren realms where the huge 

 granite rocks rise in stately grandeur around the struggling 

 waters of the Nile as they force their way through the narrow 

 channels of the Cataract. The granite rocks bind the river 

 so closely on either side throughout its course between the 

 First and Second Cataracts, that they leave but a slight margin 

 on its banks for cultivation in Nubia, which country is almost 

 entirely composed of these rocks, with here and there a lime- 

 stone mountain, the whole surmounted by the sandstone 

 strata, which has been much worn away, and in some parts 

 almost entirely decomposed into loose sand, forming in many 

 places " dunes." 



The crystalline rocks are of two kinds, viz. a rich pink 

 granite, by far the most abundant, and " greenstone," which 

 forms dykes through it. These dykes are well exhibited at 

 the First Cataract, and appear to run very constantly from east 

 to west, owing to their being more easily decomposed than 

 the surrounding granite; the water-courses of the Cataract 

 almost invariably follow their directions. They show the 

 line of very ancient prehistoric volcanic action in a country 

 which appears ever since to have remained remarkably un- 

 disturbed by subterranean fires ; for, except at the junction of 



