A Little-Known Region in Northwestern Montana. 201 
Whether these advances and retreats were annual I could not tell. We 
camped for the night near the banks of one of the milky streams flow¬ 
ing from the ice, and found in the morning that the volume of the 
stream had fallen off about one-third, and the water was much clearer. 
I concluded therefore that not only the melting, but the motion also of 
this glacier depends largely on the heat of the sun. The slope on which 
it lies is quite gentle. A few miles down the valley an older moraine, 
some four miles in length but much lower than the present moraine, in¬ 
dicates a stage in the recession of the large glacier of which the present 
is the shrunken remnant only. The glacier just described was the 
largest seen close at hand. Indeed only one was seen in the whole 
region that was larger. This, if it be a true glacier, is much the largest 
in the United States, exclusive of Alaska.* We saw it from many points, 
at distances varying from eight to twenty miles. It lies in a horse shoe 
shaped basin or valley at an elevation of about 7,000 feet and covers, as 
near as I could estimate, an area about four by six miles in extent. We 
passed half way around it but did not find the stream that must flow 
away from it, unless a somewhat remarkable branch of the Belly River 
has its source there. This stream flows out from the foot of a precipi¬ 
tous wall, fully 2,000 feet high, forming the northeast face of the conti¬ 
nental divide. The rocky wall has not a fissure in its face from top to 
bottom. The ice field lies on the opposite side of the ridge fully ten 
miles away and 2,000 feet above the point where the stream comes forth. 
The latter has the milky character common to glacial streams and flows 
from the direction of the large ice field. The strata dip from the ice 
field in the direction of the stream. Further evidence of its relation¬ 
ship must await future investigation. 
ft 
FORMER GLACIERS. 
Western border of drift. — So far as my observations extended the 
portion of the plains traversed by us is entirely devoid of drift material, 
with exceptions hereafter noted. Dr. G. M. Dawson,| in a journey from 
Fort Benton on the Missouri, to Fort McLeod, British Columbia, found 
bowlders all the way. As his route was some sixty or more miles east of 
mine, it would seem that the western limit of drift material lies between 
these two routes, and as Dr. Dawson found undoubted Laurentian 
erratics at or near the 113th meridian on the international boundary, 
it is likely that the western limit of drift for 100 miles south of the 
boundary is somewhere from forty to fifty miles east of the base of the 
mountains. 
Ice tongues of the eastern slope of Rocky Mountains .—Several ice 
tongues have at some time descended from the range on the west and 
* The location of the large glacier was in some way left out from the original map. Its 
location on the present map is only a guess at the correct place. 
t Report of Progress of Geol. Survey of Canada, 1882-84, p. 147C. 
