18 



Park Range is a member of a great anticlinal, of which the 

 Sawatch is the nucleus or central axis. This valley coming 

 between these ranges was thus first opened by fissure, and 

 then the enormous work of erosion commenced. At first the 

 valley must have had a huge glacier running from north to 

 south through its length, as there are still traces of such a gla- 

 cier in the markings on the sides of the mountains and in the 

 drift matter on its slopes. Then part of this valley formed 

 the bed of a large lake, as is shown by the deposits in the 

 bottoms where they are exposed. This lake occupied the 

 lower half of the valley, and when it was drained off through 

 the opening now traversed by the Arkansas River the heavy 

 and coarse material at the upper end and the finer drift matter 

 at the lower end were exposed. The valley has many rounded 

 oblong hills, which are covered by debris, and range in 

 height from 500 to 700 feet. After this first large glacier 

 came others, which might be called secondary, and occu- 

 pied the beds of the present tributary streams of the 

 Arkansas. Each one of these is marked by large moraines, 

 and where exposed, the glaciation is magnificent. The 

 masses of rock which have been transported by these agencies 

 are incredibly large, often reaching 100 feet in diameter. The 

 largest of these valleys is that of Lake Creek. This whole 

 valley must have been occupied by a glacier of from 1000 to 

 1500 feet in depth. The terminal moraines of this glacier are 

 remarkable for their size. Everywhere the traveller is hin- 

 dered in his journey by mounds, ridges, basins and boulders, 

 the latter often from 20 to 50 feet in diameter. Worn rocks 

 are also exposed, showing the effect of ice on their surfaces. 

 The upper part of the valley has two lakes in it, whose basins 

 were doubtless formed by the glaciers. These lakes are 

 about 350 yards apart and connected by a small stream. The 

 lower of these lakes is the largest, being 2-J- miles in length 

 and ij in breadth, its greatest depth being 75 feet. The 

 upper lake is I mile in length and mile in breadth, having 

 a depth of 79 feet. 



On either side of this valley are the Sawatch and Park 

 Ranges, the origin of which we have already indicated. The 

 great mass of the Sawatch Range is a granite nucleus, with 

 now and then a dike of some foreign material. There is one 



