2 9 6 LEWIS G. WESTGATE 



toward the mountains have every appearance of alluvial fans. To 

 the writer, who came into the region after several weeks in the Utah 

 portion of the Great Basin, where the long slope of alluvial wash at 

 the base of the mountain ranges is a striking feature, their topographic 

 resemblance to alluvial fans was very strong. 



The question may be raised as .to the possibility Of damming by 

 the glaciers entering the Arkansas valley. The moraine of the earlier 

 Lake glacier does not appear to have reached the present Arkansas 

 by a half-mile, and cannot have dammed up the stream. Further 

 the height of the gravels above and below Lake Creek is essentially 

 the same. At Clear Creek the conditions are different. Here the 

 old moraine lies along the western edge of the gorge, and the height 

 of the gravels to the north seems to be determined by the rock-level 

 at the top of the gorge outside of the moraine. The Arkansas was 

 pushed to its present position on the east side of the valley by the 

 advancing moraine of the Clear Creek glacier, and the height of the 

 gravels up-stream determined by the position of that moraine. This 

 does not necessarily mean, however, that a lake was formed to the 

 north; the character of the gravels is against that interpretation. 

 The probable explanation is that in earlier glacial time the advance 

 of the Clear Creek glacier and moraine went on contemporaneously 

 with aggradation by the Arkansas, until at the maximum the Arkansas 

 was flowing on its flood-plain about the nose of the Clear Creek 

 moraine, pushed to that position by the gradual advance of the glacier. 

 Farther north also the Arkansas hugs the east side of its valley. 

 This, however, is not due to pushing by glaciers, but probably to a 

 greater supply of detritus coming in from the glaciated valley of Lake 

 Creek, building a wash-plain with slope to the west, and constantly 

 tending to push the main stream to the east. 



2. The work of inter glacial time. — Glacial periods are times of 

 valley-clogging; interglacial periods, of valley-cutting. The first 

 glacial period with its moraines and gravels was succeeded by an 

 interglacial period in which the Arkansas and its tributaries were 

 -engaged in valley-cutting. To this period is assigned the excavation 

 of the rock-gorge of the Arkansas. From a point two miles north of 

 Lake Creek, south to beyond Granite, the Arkansas was flowing on 

 the east side of its own gravel deposits and well to the east of its 



