288 LEWIS G. WESTGATE 



I. MORAINIC SYSTEM OF LAKE GLACIER 



i. Two periods o] glaciation. — The moraines of the Lake Glacier 

 form a rough semi-circle on the west side of the Arkansas, reaching 

 almost to the present Arkansas River. 1 Within this area moraines 

 of two distinct dates are found, separated by a time interval of suffi- 

 cient length to constitute two separate glacial periods. Their dis- 

 tribution is shown on the accompanying map (Fig. i). The later 

 drift forms a continuous moraine about the lakes. The earlier drift 

 occurs outside the later drift for four miles north of Lake Creek, and 

 at one or two isolated points south. The evidence for the different 

 age of the two moraines lies (A) in the relations which they hold to 

 the gravels of the Arkansas valley, (B) in the difference in weathering 

 in the two moraines and gravel-plains, and (C) in differences of 

 topographic expression and amount of stream-dissection of the two 

 moraines and their correlated gravels. 



A. Relation of moraines to gravels. Two series of gravels occur 

 along the Arkansas. One is a succession of terrace fragments, lying 

 within the interglacial gorge of the Arkansas and rising some 30 to 40 

 feet above the river. At Lake Creek this terrace rises somewhat 

 steeply to the front of the later moraine, and the relations of the two 

 show clearly that the gravel is a wash-plain formed by the glacial 

 waters contemporaneously with the accumulation of the moraine. 

 The later moraine is therefore of later date than the cutting of the 

 rock-gorge of the Arkansas. 



A second series of gravels occurs up to 400 feet above the river-level, 

 back from the upper edge of the rock-gorge, and on both sides of the 

 river. East of the river they form in places a thin veneer over the 

 graded rock-plain of the preglacial Arkansas; in large part, however, 

 they are represented only by scattered bowlders. 2 West of the river 

 they form extensive terraces. That the deposits were originally 

 continuous is shown by their occurrence at the same levels on both 



1 There is no evidence that the Upper Arkansas was ever occupied by a north- 

 and-south master-glacier, as suggested by Hayden, Annual Report for 1873, p. 48. 



2 Referred to by Capps and Lefnngwell {Journal of Geology, Vol. XII, p. 702) as 

 possibly indicating a third period of glaciation earlier than the two to be mentioned 

 later. They seem to be associated, however, with the upper terrace gravels, though 

 floating ice may have had some share in bringing them to their present condition, as 

 they are sometimes 2 to 3 feet in diameter. 



