PLEISTOCENE GEOLOGY. 265 



GLACIO-NATANT DRIFT. 



"Wherever in the Denver Basin a good exposure of the contact between 

 the loess and the underlying sandstones is observed, the bed-rock is gener- 

 ally found to lie strewn more or less thickly with rock debris that must 

 have been brought from a considerable distance. It is often found not 

 directly at the contact hut suspended in the body of the loess up to a dis- 

 tance of 2 or 3 feet from the bed rock. This debris is mostly well rounded, 

 though angular fragments are occasionally found. The size of the frag- 

 ments mostly exceeds the power of transportation of streams of the present 

 day. and sometimes attains a yard in diameter. They are frequently 

 covered by a coating of calcareous cement, up to an inch in thickness. 



On eminences below the level of 5,800 feet, from which the loess has 

 been mostly or entirely removed, the former presence of this drift is 

 indicated by the bowlders left on the surface, which, in such cases, can 

 be distinguished from the upland drift only by their calcareous coating! 

 The presence of the drift is also indicated, where the loess still remains, 

 by bowlders taken out from wells just before the sandstone' bed rock is 

 reached. The vicinity of Denver is consequently the best place to observe 

 it, and it is characteristically shown on the hills near Berkeley Lake, 

 Overland Park, and the former Gentlemen's Driving Park; also on the 

 mesa between Bear and Clear creeks and the Platte River. A considerable 

 portion of the drift on Capitol Hill, in Denver, has been derived from the 

 neighborhood of Dawsons Butte, which is 40 miles distant. It is noticeable 

 that material from the Arkansas divide region is rarely, if ever, found on 

 the north and west side of the Platte; nor is the material from the mountains 

 ahout ( rolden, which is strewn abundantly over the hills west of the Platte, 

 found to the east of it. The small grains of sand in the loess show a like 

 diversity of origin with the stones in the glacio-natant drifts. 



Where an ancient river lied is covered by the loess, the large number 

 of pebbles derived from the head waters of the stream that occur in the 

 loess will often serve to indicate the former course of the- stream. Thus a. 

 considerable portion of the ancient channel of Sand Creek is now buried 

 under a northern continuation of Capitol Hill, and may lie traced by 



