GLACIATION OF THE UINTA MOUNTAINS 801 
outward, around the margin of the ice field, would work these steps 
or benches farther and farther back. Sometimes a very resistant 
layer of quartzite served for several square miles as a base to which 
the quarrying work of the ice went on. Then another resistant layer, 
10, 20, or even 200 to 300 feet higher, would serve as the floor of the 
quarry. ‘The work therefore went on in something of the fashion in 
which men widen and deepen quarries in similar formations. Many 
abandoned benches remain today about the margins of the great 
catchment areas. 
Corresponding to the widening of the basins, there was a narrow- 
ing of the divides between the heads of the canyons and of the main 
crest of the range. Some of the divides (see Fig. 3) were so reduced 
that it is dangerous to try to walk along them. Others were sur- 
mounted and greatly reduced by the ice. The main crest-line was 
sharpened, and the peaks were given greater prominence. 
In the canyons the great change was the development of the 
broad U-shaped troughs. The preglacial forms were largely oblit- 
erated. ‘The canyons were widened and deepened. In this process 
many tributaries were left as hanging valleys with their lower ends 
several hundred feet above the main stream. Preglacial erosion 
lines, and asperities common to the slopes of unglaciated canyons, 
were commonly rubbed off as far up as the ice rested. 
In the bottom of the gorges, on the canyon walls, and in the basins, 
the glaciers built up new topographic forms. The terminal moraines 
have an average depth of about 4oo feet. In one instance, however, 
it is clear that there is at least 1,000 feet of morainic material at the 
mouth of the canyon. ‘These moraines are often ridgelike in form but 
where the glaciers pushed out on the lowlands bordering the mountain 
range, they have a hummocky topography similar to the terminal 
moraines left by the continental ice sheet of the interior region. At 
intervals, up stream from the terminal moraine it is customary to 
find other morainic ridges or belts crossing the valley in the manner 
of recessional moraines. Above these recessional moraines lakes are 
sometimes located, but more commonly swamps, which are being 
drained as the main streams lower their courses through the morainic 
dams. The lateral moraines are lodged as ridgelike forms on the 
valley slopes. The crest-lines of these lateral ridges increase in 
