JUNCTION OF LAURENTIDE AND GORDILLEEAN DRIFT. 121 



main eastern range of the Rocky Mountains that it outflowed eastward 

 through the passes, carrying diorite bowlders from ledges west of the 

 watershed to a distance of several miles on the plains at the eastern base 

 of the mountains. No Laureutian drift was observed there, but in the 

 valley at the head of St. Marys River, a tributary of the Belly River, on 

 longitude 113° 30', .5 to 20 miles south of the international boundary, 

 shore-lines of a glacial lake," which was probably formed by the neighbor- 

 ing barrier of tlie Laurentide ice-sheet on the northeast, occur up to the 

 height of at least 800 feet above the present St. Mar_ys lakes, or approx- 

 imately 5,400 feet above the sea.^ 



In the neighborhood of Calgary, which is the western limit of Lau- 

 reutian bowlders and till, Dawson reports somewhat farther westward a 

 deposit resembling bowlder-clay, in which the stones "are entirely those of 

 the mountains or sandstone blocks from tlie underlving beds." Accord- 

 ingly, he declares that the absence of Laureutian erratics west of Calgary 

 is probably to be accounted for "by the existence of Rocky Mountain 

 glaciers of suflieient size in this region to fend off the eastern glaciating 

 agent." Again, he mentions, west of Calgary, "heaw glacial striation in 

 a southward or southeastward direction * * * aljout 13 miles ea.st of 

 the mountains, in a region of wide vallevs and low foothills."" 



On the Peace River, in its course close east of the Rocky Mountains, 

 and on its tributarv. Pine River, Dawson reports drift containing a large 

 proportion of "hard (juartzite pebbles like the more resistant materials of 

 the axial range of the Rocky Mountains. These are mingled with a pre- 

 ponderating number of fragments of the softer sandstones of the countrj-, 

 and embedded in a Avhitish or cream-colored silty clay, not unlike the 

 material representing the bowlder-clay over wide districts west of the 

 Rocky Mountains. No Laureutian or other fragments of eastern origin 

 were observed in this region." Continuing eastward, these drift deposits 

 become more conspicuous, attaining in places a thickness of loO feet. On 

 reaching the D'Ecliafaud River, about 100 miles from the mountains, 



'"Notes on a little-kuown region in northwestern Montana," Transactious, Wisconsin Academy 

 of Science, Arts, and Letters, Vol. VIII, pp. 187-205, with map, Dec. 30, 1891. 



-Geol. and Nat. Hist. Survey of Canada. Report of Progress, 1882-84. pp. 140 C, 151 C ; Annual 

 Report, new series. Vol. I. for 1885, p. 167 B. 



