THE TWIN LAKES GLACIATED AREA 29 1 



by much larger streams in the younger drift — as, for example, the 

 valley of Lake Creek where it crosses the moraine — and point to the 

 gravels being much older. There is reason to believe that the streams 

 entering the Arkansas from the west between Lake Creek and Clear 

 Creek have, by widening their valleys until they joined, succeeded 

 in reducing the whole level of the upper gravel deposits some distance 

 below its original height. The dry valleys which cross the gravel 

 terrace north of Lake Creek head, as has been mentioned, in the 

 older moraine. Their continuation from the river with essentially 

 unchanged dimensions and expression, back across the gravel terrace 

 into the older moraine, but not into the younger moraine, shows 

 the connection of the older moraine and the higher gravels. The 

 younger moraine is not eroded by any drainage originating on the 

 moraine itself. 



The relation of the moraine to the gravels shows that the valley 

 of Lake Creek was at two distinct periods in Pleistocene time occupied 

 by a glacier, and that these two periods were separated by time 

 enough for the cutting of the rock-gorge of the Arkansas. And the 

 much greater weathering and erosion of the older deposits indicate 

 that interglacial time was much longer than postglacial time, in this 

 region. 



2. The earlier moraine. — The character of the older drift is well 

 shown outside the younger moraine north of Lake Creek. Here, 

 toward the south, it forms a low terrace several hundred feet wide 

 rising some 30 to 50 feet above the wash-plain which fronts it. From 

 a distance it looks almost like a second terrace rising above the general 

 level of the upper terrace, but its surface is rolling and uneven. It 

 is usually separated from the younger moraine by a shallow valley. 

 Its surafce, while rolling, is less uneven and rocky than that of the 

 younger drift; scattered erratics up to 6 or 8 feet in length are com- 

 mon over its surface, but these do not reach the size of those on the 

 other moraine. Northwest, this terrace widens to about a mile, 

 forming a gentle slope away from the later moraine to the wash-plain 

 nearer the river. This older drift has not been traced beyond the 

 Twin Lakes-Hayden road. 



The older drift is mapped at two places south of Lake Creek. 

 The western of these two occurrences (Fig. 1, 4) is not large enough 



