562 PROCEEDINGS OF THE ALBUQUERQUE MEETING 



branches, the north and the east. It is probable that the latter contains the 

 glacier, for Professor Wolff and Mr Merwin, who examined the north branch, 

 found no evidence of it in that canyon. The east branch was not visited by 

 the party. 



Effects of Glaciation 



CIRQUES AND HANGING VALLBTS 



All the higher valleys in both sections of the moimtaius have cirques at 

 their heads. The steep or precipitous walls are usually well marked, but often 

 later accumulations of slide rock have modified to some extent the earlier out- 

 lines. In the northern section of the mountains cirques occur mainly in the 

 region of Loco mountain, the highest summit, where they cut sharply into the 

 gentle, ancient topography of the mountain. In the southern section cirques 

 occur throughout the area above the foothills, and, where adjacent cirques 

 worked backward on opposite sides of divides, sharp arretes have been pro- 

 duced. Two-story cirques occur in a number of places, fine examples having 

 been observed near the supposed glacier in Sweetgrass canyon and in the north 

 fork of Rock creek. Plate 35, figure 2, shows a beautiful cirque, with lakelet 

 at the head of the north branch of the south fork of Swamp creek. 



Hanging valleys may be seen on the sides of the larger canyons. Good ex- 

 amples occur in the canyons of Big Timber, Sweetgrass, and Rock creeks. 

 Plates 36 and 37, figure 1, show hanging valleys in Rock canyon and Big 

 Timber canyon i-espectively. In each case the upper valley hangs at least 600 

 feet above the main trough floor. In plate 37, figure 1, the hanging valley 

 on the south side (left of picture) consists really of at least four shallow 

 troughs, each separated from its neighbor by a low rock ridge, and each repre- 

 senting the outflow from a separate cirque. Near the rim these subordinate 

 troughs unite, and send their drainage out through a branching stream that 

 leaps in a double series of small cascades to the floor of the main valley below. 

 Two other subordinate notches occur in the rim, but these contain no streams. 

 Apparently the combined output of ice from the several cirques was insuffi- 

 cient in quantity, and worked for too brief a time to efface the low boundary 

 ridges of the minof ti-oughs, so that, while the surfaces of the contributing ice 

 streams doubtless joined, the streams themselves were enabled to maintain 

 their individuality almost to the very rim. 



TROUGHS 



The lower canyons have broad, flaring, trough-like cross-sections, and the 

 trough constitutes nearly all, or, indeed, the entire valley (see plate 37, figure 

 2). In the upper canyons, where the hard rocky core of the high mountains 

 is penetrated, the troughs form a much smaller proportion of the valleys, and 

 the latter appear rather broadly Y-shaped. In plate 37, figure 1, the main 

 valley of Big Timber creek is seen to have long slopes of normal erosion above 

 the top of the glacial trough. This relation seems to hold throughout the 

 higher parts of the mountains. The valleys are in the main rather straight, 

 and the spurs that would normally enter from the side have been cut back. 

 This truncation is not, however, limited to the slopes included within the 

 troughs, but extends as well to the upper slopes that have not been glaciated. 

 Thus the glacial troughs seem to have been formed in valleys that had already 



