6 The Ancient Glaciers of the Rocky Mountains, (January, 
ing the barrier of Mount Washburn, cannot have been less than 
1650 feet thick (=the height of the three feet boulder on the 
crest of the ridge), and probably was at least 1900 feet (= the 
height of the highest observed block). That mountain project- 
ing as a great barrier in the pathway of the ice served to ridge it 
up, and no doubt partly to deflect it. I observed a granite block 
south of Dunraven pass, on the south side of the mountain, ata 
height of 8600 feet, and moraine-stuff and erratics, at intervals, 
down to the very edge of the Grand cajion, and beyond even as 
far as the water-shed of the Fire Hole river. Whether Grand 
cafion existed in glacial times, I found no evidence to prove; but 
I am inclined to believe that it probably existed only in a rudi- 
mentary condition, and has been mainly excavated since that 
period. 
From the evidence here cited, it is clear that the ice of the 
Yellowstone valley was more than that.of a mere local or valley 
glacier. It was massive enough to fill up the main valley and 
override the surrounding hills, crossing minor water-sheds and 
spreading into adjacent drainage basins. From elevated points in 
the Yellowstone valley, the distant outlines of the Wind River 
mountain or their northward prolongation can be seen to the— 
south-east, while southward rises the lofty peaks of the Tetons. 
That these mountains, though not within the present water- 
drainage basin of the Yellowstone, were within the ice-drainage 
of the ancient glacier of that valley, is, I think, extremely prob- 
able. The abundant blocks of granite and granitoid gneiss lying 
within the volcanic area of the Upper Yellowstone, seein to have 
been derived from cliffs outside the basin. Of course I had no 
opportunity of tracing them to their source. But I could hardly 
doubt that it will be found in the central archzan cores of these 
distant mountains. Should this view be confirmed, it will supply 
an additional proof of the magnitude of these ancient glaciers, 
for it will show that the snow fields of the Wind River and Teton 
' ranges were so extensive that their ice rivers streamed northward 
across the buried water-shed, and poured into the basin of the 
Yellowstone. According to Dr, Endlich, the old glaciers on the 
west side of the Wind River mountains pushed their way out 2 
into the plateau country for several miles, and piled up moraines 
there to a height of 800 or goo feet. It is much to be desired by 
all who take an interest in glacial geology, that an exploration 
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