298 LEWIS G. WESTGATE 



come down the face of Lost Canyon Mountain, cross the plain, and 

 enter the Arkansas. Only one of these, Cache Creek, is a permanent 

 stream, but the others carry much more water than the channels 

 which head in the moraine to the north of Lake Creek. The effect 

 of their combined action is that the original surface has been cut into 

 series of eastward-sloping terraces, whose level is determined by the 

 distance the streams have cut into the rocky edge of the Arkansas 

 gorge — levels which are lowest toward the south, where Cache Creek 

 cuts deepest toward the river. These valleys have widened till they 

 met, and in this manner the original constructional level of the terrace 

 has been replaced by a terrace of stream-erosion. The only points 

 where the original surface is kept are on the salients at the base of Lost 

 Canyon Mountain, where the gravels have been protected from erosion 

 by their position on the divide between the small valleys crossing the 

 plain. Here the gravels rise to the level of the gravel fragments east 

 of the river and north of Lake Creek. At one point nearer the river 

 a remnant of the higher level is kept. A small hill just south of Lake 

 Creek on the west side of the Arkansas rises 50 feet above the general 

 level of the plain in its neighborhood. The part above the surround- 

 ing terrace-level is rock with a covering of gravel. This is a remnant, 

 not of the original terrace, for it is covered with quartzite gravel 

 derived from north of the Lake Creek region, but of an intermediate 

 terrace which stood above the present terrace-level; and it is a witness 

 to the general degradation of this part of the old plain. The Arkansas 

 here cut across a shoulder of granite coming from the east, and this 

 granite nucleus has preserved the gravel over it from removal. 



The cutting of interglacial time was marked by the development 

 of terraces (F in Fig. 3) at intermediate levels. The benches so pro- 

 duced are not conspicuous features of the topography, and are deter- 

 mined by the levels at which the streams came upon rock barriers 

 as they cut through the gravels to the underlying rock. One such 

 terrace is cut in the high gravels along the east side of the Arkansas 

 opposite Hayden, and is determined by the highest rock-level in the 

 gorge to the south. At this level in the gorge a narrow terrace is 

 worked out in the rock. The gravel on these intermediate terraces 

 is largely composed of quartzite bowlders of medium size, while the 

 bowlders of the upper terrace are largely granitic in composition and 



