GLACIATION IN THE TELLURIDE QUADRANGLE 723 
60 feet in depth. As to the outer boundary of these areas, the 
degree of slope is often as steep as can be formed by the fragments 
composing it. This is true both of the sides where the rock stream 
extends as a tongue down the valley, and of the lower end or 
terminal portion. In some cases, as in the area in Turkey basin 
(Figs. 10 and ir), the fragments making up the outer slope were 
found so insecure in their position as to make climbing difficult, 
numerous fragments sliding and falling down the slope whenever 
an attempt was made to secure a foothold. 
In a few cases, as for example in Middle basin, a valley tributary 
to the valley drained by Marshall Creek, in the upper part of the 
valley of the tributary of Mill Creek heading west of Dallas Peak, 
in Savage basin, and in Ingram basin, rock streams of at least two 
distinctly different ages occur. The more recent is composed of 
fragments fresh in appearance, angular, and bare except for lichens 
on some of the surfaces. In the case of the older, the rock fragments 
are much disintegrated, so that the crests of the ridges are less sharp, 
and soil enough has accumulated to support vegetation, making the 
surface appearance that of rounded, green hills instead of bare 
ridges of angular fragments. These rock streams of earlier age 
usually lie at the lower or outer edge of the corresponding areas of 
more recent date, but in at least one case, in the upper part of Savage 
basin just beyond the eastern boundary of the quadrangle, the 
stream of unweathered fragments has passed around and beyond a 
small area of the earlier, appearing to have been deflected in its 
movement as by an obstacle, but spreading out again below the 
obstruction after having passed it. 
To account for the presence of these accumulations of rock 
fragments two principal causes have been assigned, namely, (1) 
landslides, moving ‘“‘with a sudden violent rush that ended as 
quickly as it started,” and (2) the effect of the presence of inter- 
stitial ice, cementing the fragments together, and producing with 
changes of temperature a movement similar to that of glaciers. 
The former view is advanced by Howe in Professional Paper 67, U.S. 
Geological Survey, p. 54; the latter by Capps, in the Journal of 
Geology, XVIII (May-June, ro10), 362-64. Each of these authors 
recognizes other possible causes, but considers such others as may 
