IOWA ACADEMY OP SCIENCES. HI 



TERRACES OF THE NILE VALLEY. 



BY CHARLES R. KEYES. 



(Abstract.) 



Erosion forms in regions of very dry climates are always of 

 great interest. The characteristic relief outlines are not only 

 preserved much longer than in regions of abundant rainfall, 

 but the types of different cycles or parts of cycles are not 

 merged with one another. In other words, the sequence of 

 events is read at a glance in the one district, while in the 

 second it is made out only partially after long and laborious 

 effort. The Great Basin is the best example in this country. 



In the Nile valley, in lower Egypt, there is a similar group 

 of conditions presented that we find in the Great Basin. The 

 annual amount of rainfall is so scant (only about one inch) 

 that the older European geologists who have visited the great 

 delta and the valley opening out to the south have been unable 

 to ascribe any of the hill terraces to the action of water. They 

 have been pretty well agreed in considering the terraces as 

 the result of faulting, though admitting that the terrace 

 courses are remarkably sinuous and angular. 



In some places the faces of the terraces do resemble fault- 

 scarps. The appearance of some of these are shown in the 

 accompanying photographs which represent the approach to 

 the Mokattam hills, which form the high ground on the east 

 side of the Nile, near Cairo. The photographs were obtained 

 a few months ago while on a visit to the Nile country in com- 

 pany with Mr. Alexis Pry, of Boston, and Dr. Woodrow, of 

 Columbia. 



In the waddies, or deep ravines, running back from the main 

 Nile escarpment the terraces are found to follow all the wind- 

 ings for several miles at least. Those of the several different 

 levels are easily traced. Their concidence with the terraces 

 of the mam escarpment bordering the Nile precludes the idea 

 of faulting as a satisfactory explanation of the terrace forms. 



It is manifest in the waddies that torrent action is vigorous, 

 though of course at irregular and long intervals. Moreover, 



