588 PRINCIPLES OF STRATIGRAPHY 



deep. Other waste basins of this kind are found in Spain, Italy, 

 and elsewhere. 



In arid regions the basins often have an inward drainage and 

 are filled by the combined atmoclastic creep and the river wash. 

 P^ans with their heads rising 500 feet or more above their bases 

 and extending 10 or 15 miles outward characterize such basins. 

 The water of the stream evaporates or sinks into the ground be- 

 fore the center of the basin is reached. When such fans become 

 confluent they form huge waste plains of relatively steep grade, 

 filling the valleys and partly burying the mountain slopes. In Utah, 

 Nevada, and Arizona depressions of great depth have thus been 

 wholly filled, while the waste mantle backs up 2,000 or 3,000 feet 

 on the mountain flanks. 



"A great part of Persia consists of large basins enclosed by 

 mountains and without outlet to the sea. Long waste slopes stretch 

 forward 5 or 10 miles with a descent of 1,000 or 2,000 feet, stony 

 near the mountain flanks, and gradually becoming finer-textured 

 and more nearly level. The central depressions are absolute deserts 

 of drifting sands, with occasional saline lakes or marshes. 



"Central Asia repeats the same conditions on a still larger scale. 

 The basin of eastern Turkestan includes many half buried ranges 

 in its central part. It is quite possible that some ranges are com- 

 pletely covered with waste. JNIaliy rivers flowing from the moun- 

 tain rim wither on their way toward the chief central depression ; 

 only the largest river (Tarim) reaches it, there spreading out in 

 Lob (Lake) Nor. The chief settlements are near the border of 

 the -basin, where the larger rivers come out from the mountains." 

 (Davis-iSij//.) 



The deposits of these regions must be considered as in part at 

 least of purely atmoclastic and anemoclastic origin. 



River Flood Plains. River flood plains vary enormously in 

 extent as well as in the character of the material. Streams with 

 relatively steeply sloping beds may have stony flood plains, if they 

 are abundantly supplied with coarse detritus from the head and 

 sides. The flood plain of the Saco in the Intervale is covered with 

 rounded cobbles and boulders, these often forming a regular cobble- 

 stone pavement. The stream is a rushing one, and in flood carries 

 away all the finer material. A large part of the boulders and 

 cobbles is formed of the granite of which this part of the White 

 Mountain region is composed, but a part of the material at least 

 is derived by the rehandling of flood-plain deposits formed during 

 the preceding flooded stage period controlled by the melting ice of 

 the glacial period. 



