204 Wisconsin Academy of Scieaces, Arts and Letters. 
There are many other exposures on the upper waters of McDonald’s 
Creek, where the diorite is the surface formation and is strongly glaciated. 
On the divide between the East Kootanie and McDonald’s Creek, the slop¬ 
ing west wall of the common valley is a bed of this diorite. It has been 
planed and smoothed for a thousand feet from the bottom of the valley 
by the ice stream that once flowed through this gap. 
In brief, then, the evidence is this: 
1. Trains of diorite bowlders were traced from the plains east of the 
mountains up to the axis of the range, along three lines widely separated 
from each other. 
2. No outcrops of diorite could be found on the eastern slope on any 
of these lines. 
3. Extensive, heavily glaciated outcrops occur on the western slope 
1,000 feet below the summit of Ahern Pass. 
4. On the Belly Diver line, the bowlder train was followed over the 
summit of Ahern Pass, down the western slope to the parent ledge. 
From these facts, then, it seems clear that the ice-tongues which crept 
down the valleys on the east slope of the Rockies, and plowed their way 
out some miles beyond the foot-hills, did not originate on the east side 
of the range; but were pushed up over the continental divide through 
the gaps and passes mentioned, and probably through others not yet 
examined, by some force from the west. What that force was, admits of 
but little question. That it was an ice sheet of some vigor is obvious. 
That it was separate and distinct from the Laurentian ice sheet, at least 
to high latitudes, is equally clear. Dr. Dawson has brought forward 
evidence * to show that a great ice sheet which he has called the Cordil- 
leraii Glacier once occupied the region between the Coast Range and 
the Rocky Mountains in British Columbia, and later he has found evi¬ 
dence | that the ice ran through the gaps in the Coast Range and down 
to the sea. 
President Chamberlin J has shown that the ice extended southwest to 
the vicinity of Lake Pend d’ Oreille, Idaho. Mr. Bailey § Willis has 
found similar evidences in Washington. Neither of these observers, 
however, connect the ice records seen by them with the Cordilleran 
Glacier. 
From such observations as I was able to make, it is my impression that 
the ice ran in the valleys, in streams whose courses were determined 
partly by the source but mainly by the mountain topography. The re¬ 
gion lying between the main range on the east, the Rocky Mountains 
* Quart. Joui\ Geol. Soc., vol. 31, p. 89, and Quart. Jour. G-eol. Soc., vol. 34, p. 72 . 
■(■ G-eol. Mag. Decade III, vol. 5, 1888, p. 347. 
tBulletin No. 40, U. S. G. S. 
§Ibid. 
