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THE POPULAR SCIENCE MONTHLY. 



stream runs througli unstratified rocks, in a district well supplied 

 with rains, the walls or banks of the stream are cut down in more 

 gentle slopes. 



For purposes of discussion, it will be convenient to call the deep 



V 



Section op Wall in the Grand CaSon. 



channels of streams through table-lands, in arid climates, caiSons ; and 

 the deep channels of streams through heterogeneous beds, in a moist 

 climate, water-gaps, or narrows, and ravines. 



