36o STEPHEN R. CAPPS, JR. 



present, however, I have called rock glaciers. These rock glaciers 

 occur in unusual numbers and attain exceptionally perfect develop- 

 ment on the Nizina Special Quadrangle, where I had an opportunity 

 to study them in the summer of 1909 while working on the geology 

 of the region in a U.S. Geological Survey party in charge of Mr. F. H. 

 Moffitt. The center of the area lies at longitude 143° 40' W., latitude 

 61° 20' N. On the sheet there are more than 30 of these rock glaciers 

 and the valleys which they occupy are in every case cirques excavated 

 at the time of the maximum glaciation of these mountains. The 

 valleys are still on the very border line of glacial conditions, and in 

 fact many of them still have small glaciers at their heads. The great 

 Kennicott Glacier, in the main Kennicott Valley, occupies the bottom 

 of the valley into which many of the rock glaciers discharge. Fig. i 

 is a topographic map of a portion of the area. 



In material the rock glaciers are composed of angular talus, such 

 as goes to make up the ordinary talus slope, the kind of rock being 

 that of the cirque walls above — porphyry, limestone, greenstone, or 

 shale. In most cases the fragmented rock extends all the way to the 

 head of the cirque, with no ice visible and with little or no snow on 

 the surface. In several instances, however, the rock glaciers grade 

 into true glaciers at their upper ends, without perceptible break. 

 There is, therefore, a complete gradation between the two. 



They vary greatly in size, but are usually many times longer than 

 wide, occupying, as they do, the bottoms of cirque-like valleys. Some 

 have wide, fan-shaped heads, and narrow down to a tongue below. 

 Others are narrow above, and deploy into spatulate lobes below 

 (Fig. I, No. i). Still others are formed by the junction in a valley 

 of rock glaciers from two or more tributary valleys (Fig. i, No. 5), 

 but the greater number are narrow bodies of nearly uniform width, 

 from one-tenth to one-fourth of a mile wide and from one-half to two 

 and one-half miles long. The surface slopes vary in different cases 

 from 9° to 18° for the whole course of the rock glacier. As topographic 

 features they are well brought out on Mr. Witherspoon's topographic 

 map of the area, a portion of which is shown in Fig. i. The individ- 

 ual rock fragments are for the most part small, but attain, in excep-* 

 tional cases, a diameter of several feet. Six inches would perhaps 

 be about the average diameter in those rock glaciers which are com- ■ 



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