GEOLOGY. 811 
vinced that Dr. Foster is in error. Mr. Henry Gannett, who spent 
the summer of 1869 in South Park, and the region about Gray’s 
Peak, informs me that a number of well defined terminal moraines 
may be seen west of Gray’s Peak on the trail leading from Monte- 
zuma up the peak, and that on Clear Creek, which Dr. Foster says 
he took as his line of observation, near Fall River may be seen 
another terminal moraine. Mr. Gannett’s testimony is confirmed 
by several other members of the party he accompanied. 
Dr. Foster is undoubtedly right in saying that in the region he 
visited the rocks exhibit no traces of glacial markings. The 
granites and syenites that are first met with on entering the Rocky 
Mountains from the east are exceedingly friable and decompose 
with the greatest rapidity on exposure to the atmosphere, so that 
under these circumstances the planed and striated rock surfaces 
Would long since have disappeared. It is only when passing 
Westward, we approach the outlying spurs of the Snowy Range 
that the granites begin to be hard enough to retain any traces of 
glacial action. 
Last summer in the collecting expedition to the Rocky Moun- 
tains sent out by the Museum of Comparative Zoology, Mr. Allen 
and myself had on one occasion opportunity of observing such 
traces of ice action as to leave in our minds no doubt of the 
former existence of glaciers in those mountains. These evidences 
of glaciation we saw near Montgomery, a mining town on the 
head waters of the South Platte in the northwestern part of Park 
county. The South Platte rises in the spur of mountains running 
West from Mt. Lincoln and flows eastward for about five miles ' 
through a broad gulch, the walls of which range in height from 
eight hundred to fifteen hundred feet. From an examination of 
the exposed surfaces of the rocks forming the sides and floor o 
the guleh, made by Mr. Allen and myself, I am convinced that at 
Some former time the whole valley must have been filled with ice 
moving downward toward South Park. Wherever the rocks had 
not been disturbed by mining operations they were worn perfectly 
Smooth and deeply furrowed with glacial striæ. I noticed several 
Places Where projecting rocks were polished and furrowed on the 
Side facing up the gulch ; and left untouched on the opposite side, 
showing that the ice field had moved down the gulch toward the’ 
k. Near the lower end of the gulch I traced the glaciation to 
à height of eight hundred and more feet, or to the point where the 
