OF EGYPT. 35 



In order to givt a slight idea of the geological formation 

 of Egypt and Nubia up to the Second Cataract, and also 

 to indicate whence the ancient Egyptians procured the granite 

 and greenstone for their obelisks and statues, as well as 

 to show the general distribution throughout the country of 

 that splendid white limestone on which they executed some 

 of their finest carving, I shall give a short sketch of the 

 formations which contain them, with their general localities ; 

 for by understanding the geology of a coimtry we add con- 

 siderably to our knowledge of its physical geography. These 

 rocks may be conveniently divided, for our present con- 

 sideration, according to their mineralogical characters, into 

 foui' distinct groups, which I shall enumerate in their order of 

 superposition, beginning with the most recent. 



1. Alluvium of the Nile. — This forms the entire Delta, and 

 extends in a thin layer over all the cultivated land of Egypt 

 and Nubia, and is generally bounded on either bank by 

 cliffs. Large tracts towards its edges have in many places 

 been covered over by the sand borne from the deserts, and are 

 no longer cultivated. This alluvial soil may often be traced 

 at a considerable distance from the river by the nodules of 

 " natron" (a species of travertine) which are met with on the 

 desert sand wherever it overlies an ancient deposit of the 

 Nile. The alluvium consists of a mixture of sand and clay, 

 and is occasionally, though rarely, intersected by thin beds of 

 " natron," of the appearance of white limestone. 



2. Sandstone. — This formation overlies the limestone rocks 

 both in Egypt and Nubia. At Silsilis it shows itself in con- 

 siderable thickness, and has here been largely quarried by 

 the ancient Egyptians. It imparts at this part of the Nile- 

 valley a wilder character to the scenery than lower down the 



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