PLEISTOCENE GEOLOGY. 277 



As against the suggestion which has been made that the loess deposits 

 of the Great Plains are material that has been transported b\ the pre- 

 vailing west winds across the mountains from the arid interior basins of 

 the Cordilleran system, as were the Chinese deposits from the steppes of 

 the interior of Asia, is the negative evidence of the absence, so far as the 

 writer's observations go, of similar deposits in the higher valleys of the 

 mountains themselves. 



On an assumption, similar to that of Chamberlin, that the deposit is 

 a rearranged glacial silt, most of the above tacts can be satisfactorily 

 explained. The relative coarseness of the material would be due in part 

 to the inferior mass of ice, as compared with the great continental ice sheet, 

 which had ground it down, and in part also to the nearness to its source and 

 its consequent relatively earlier deposition, [f the sheet of water in which 

 it was deposited did not uniformly cover the entire region, the more finely 

 comminuted material, especially in the vicinity of the ice trout, might have 

 been blown into the water in considerable quantity, and thus have produced 

 some of the assorting in the final deposit which distinguishes loess in general 

 from actual glacial silt. The difficulty commences, however, when one 

 attempts to account for the water body in which this material was deposited. 

 The deposition of such finely comminuted material from a body of water 

 requires a long time and extremely tranquil conditions. It was thought at 

 first that the upper valley of the Platte might have been at one time an 

 inclosed basin, and special investigations were made for finding relics of 

 some barrier that might have inclosed it, but in vain. It was found, on the 

 contrary, that on the present watershed, between the Platte Valley and the 

 head of the Republican River, the deposits of loess are now thicker than 

 in any other part of the basin, and were probably once continuous with 

 those of Kansas and Nebraska; hence the sheet of water in which the 

 loess was deposited must have extended more or less continuously over tin- 

 whole plains area. Such a body of water, with little or no movement, 

 could not have existed with the present slope of that area, but its lied must 

 have been nearly level. 



It has already been stated 1 that since Pliocene times the Great Plains 



Rept. Geol. Explor. loth Par. (King), Vol. I, Systematic lirnl.^y, pp. iss-4*!i. 



