PLEISTOCENE GEOLOGY. 2(57 



Whatever may have been the cause, whether increased precipitation 

 or greater slope of the region, or both combined, there came a time when 

 erosion attacked the accumulations of the previous epoch. The denuding 

 agencies effected the removal of the loess from the river valleys and of 

 large portions of the river drift, leaving the remainder of the latter deposit 



in continuous ten-arcs along the Bides of the H 1-plains. They also 



deepened, for an average distance of 50 feel below their former bed-rocks, 

 the grooves through which the old streams ran. The courses of the main 

 channels do not always coincide with those of the channels of former times. 

 As a rule the excavation commenced on the sides of the stream where the 

 gravel was less thick than in the center. Lateral corrasion also made 

 incursions into the sandstone hanks, and near the mouths of the smaller 

 streams new channels, diverging from the course of the stream, have been 

 formed. The old channel of Cherry ('reek diverges from its modern 

 course and tonus the side of Capitol Hill as far as Seventeenth street, 

 where it turns toward the Platte, the characteristic gravel being found 



in cellars on Seventeenth and Eighteenth streets. The same gravel was 

 found in the excavation for the State Capitol beneath a thickness of 20 feet 

 of loess. In the smaller creeks material from formations outside of the 

 present drainage area of these streams has been derived from the river drift 

 of the old streams which extended into the region from which the erratic 

 material was obtained. Small amounts of glacio-natant drift are sometimes 

 carried into the stream from overhanging bluffs, e. g., the bluffs on Cherry 

 Creek near Shackleton Place. Large amounts of locs> were removedfrom 

 the higher elevations, and in the area bounded by the foothills, the Platte, 

 and Clear Creek often nothing remains hut the glacio-natant bowlders 

 with their white incrustations to indicate a former considerable thickness 

 of superincumbent soil. North and south of this area the amount of 

 denudation has been less; only the high ridges and knolls, protruding 

 above the general surface, exhibit the basal portion of the loess, and a 

 sandstone exposure is quite rare. 



The loess, having been deposited in layers corresponding with the 

 inequalities of the eroded sandstone floor beneath, presents surface features 

 which in their broader outlines rudely conform to the reliefs of the buried 



