362 STEPHEN R. CAPPS, JR. 



posed largely of the porphyry, while in the greenstones and limestones 

 the average size of the fragments is larger, and in the shales smaller 

 than this. 



The rock glaciers in form and position resemble true glaciers in 

 noticeable ways. They head in cirques and extend from these down 

 the valley, in cross-section being highest above the valley axis and slop- 

 ing down sharply on the sides. Some were seen to have distinct 

 lateral moraine-like ridges, and all show a more or less well-marked 

 longitudinal ridging. 



The surface markings of these rock glaciers are characteristic 

 and striking. In the upper portions there are often many parallel 

 longitudinal ridges, with depressions a few feet deep on either side. 

 The sides below the cirques are usually separated from the rock valley 

 walls by a sharp trough. Tow^ard the lower ends the longitudinal 

 ridges often become less prominent and give place to concentric 

 wrinkles paralleling the lower end of the rock glacier. At the lower 

 edges, the slope often steepens to the angle of rest for the material. 

 The whole appearance gives one a decided impression of movement, 

 as though the material had moved forward from the cirques in some- 

 what the manner of a glacier, the longitudinal lines simulating moraine 

 lines. 



The marked resemblance of these forms to glaciers led to the sus- 

 picion that ice was in some way responsible for their movement. 

 To determine whether or not this was the case a number of the rock 

 glaciers, seven or eight in all, were dug into, and in every instance clear 

 ice was found; not massive ice, however, but interstitial ice, filling 

 the cavities between the angular fragments and forming, with the rock, 

 a breccia with the ice as a matrix. The depth below the surface at 

 which ice was found varied according to the elevation of the rock 

 glacier and to the portion of it examined. Toward their lower ends 

 the ice lay too deep to be found by any shallow diggings which we had 

 time to make. Farther up, toward the cirques in which they headed, 

 the ice could usually be found within a foot or two of the surface, if 

 a depression was dug into. It was often easy to get a drink of water 

 by digging at a point where the sound of running water could be heard, 

 and in these places clear water was found running along shallow 

 courses among the ice-filled talus. 



