628 PRINCIPLES OF STRATIGRAPHY 



of the so-called Bridger of the Beaver Divide appears to represent 

 a series of conjoined alluvial fans spreading out over the banded 

 clays of the Wind River, but it is not possible to say whether the 

 gravels and sands were transported by torrential streams under 

 a dry climate or by streams whose carrying capacity had been in- 

 creased by uplift." (Sinclair and Granger-52 :7/j.) The fresh- 

 ness of the feldspars indicates that they had not been leached by 

 carbonated waters, such as might be expected to occur if they 

 were deposited in a region of high humidity. This also suggests 

 that they have not been derived from the parent rock by ordinary 

 weathering processes, but rather by temperature changes, which 

 shatter the minerals without affecting their freshness. Altogether, 

 the deposits suggest dry, not necessarily arid, climate, with rapid 

 changes of temperature and rapid transportation for short dis- 

 tances and burial beyond the reach of carbonated waters. 



The clays of the Wasatch and Wind River deposits are com- 

 monly banded, alternating beds of red and blue-green clay or of red 

 with mottled clay occurring. "The red clays are frequently streaked 

 with blue-green color along joint cracks or are traversed by anas- 

 tomosing green lines along what may have been the courses of 

 roots. The beds are lenticular in shape, varying from a few 

 inches in thickness, with little horizontal extent, to strata from 18 

 inches to 50 feet in thickness, traceable sometimes for several 

 hundred yards to a mile or more. . . . Lignite is never found 

 in the red clays, but may be present in the blue. . . ." The fos- 

 sils found in the red beds are always fragmentary, "the more re- 

 sistant parts, such as jaws and teeth, predominating. In the blue 

 and mottled clays associated skeletons ... of Coryphodon 

 w^ere found." (Sinclair and Granger-52 ://^, J75.) The microscope 

 has not revealed any essential difference between the variously 

 colored clays. 



Sinclair and Granger ascribe the color banding to the alternation 

 of moist and dry climatic conditions, though no evidence of exces- 

 sive aridity has been found ; the fauna of the red and blue bands 

 being the same. "The clays cannot owe tlieir color to different 

 sources of supply, for they are microscopically the same and the 

 alternation of color bands is too regular and of too frequent re- 

 currence to permit this inference. The red clay cannot represent 

 upland oxidized wash, for waters swift enough to carry the bone 

 fragments found in the clay would also transport rock fragments 

 of some size, and these are not found." The blue clays of the 

 Wasatch are sometimes lignitic and often afford associated skeletal 

 remains, and this suggests that they were formed during cycles 



