38 G. M. DAWSON — GLACIAL DEPOSITS OF SOUTHWESTERN ALBERTA. 



sporadic manner behind the Porcupine hills, and also by the discovery 

 of such erratics on hills of some height above the Bow river at Calgary, 

 although that place still remains the western limit in so far as the valley 

 of the Bow is concerned. 



The elevations just mentioned were not, however, the highest at which 

 Laurentian erratics were found previous to the publication of the report 

 of 1882-'84, for— 



"111 1883 several indubitable Laurentian boulders, representing three varieties 

 of granitic and gneissic rocks, were found about 20 miles north of the forty-ninth 

 parallel, at an elevation of 5,280 feet." 



These boulders occur stranded upon a morainic ridge, due to local 

 glaciers of the adjacent mountains. On a plateau to the south of the 

 Porcupine hills Laurentian stones were found, though not abundantly, 

 at a height of 4,390 feet, while similar erratics were observed to be scat- 

 tered over the high country near Milk river at a distance of from 30 to 40 

 miles from the mountains and at an elevation of 4,200 feet. The obser- 

 vations since made in the Porcupine liills enal)le considerable additions 

 to be made to our previous knowledge of the maximum height attained 

 by such eastern drift near tlie Rocky mountains. 



Digressing for a moment to places farther from the eastern base of the 

 mountains, it will be useful to remember tliat on West butte of the Sweet 

 Grass hills, 90 miles east of the mountains,'^ Laurentian fragments were 

 found to a height of 4,660 feet, while according to Mr McConnell the drift 

 of this origin finds its limiting height on the Cypress hills 200 miles from 

 the mountains, at 4,400 feet.f Both the places last mentioned are not 

 far from the forty-ninth parallel ; ])ut much farther to the north, in the 

 Hand hills (latitude 51° 25', longitude 112° 20'), Mr J. B. Tyrrell has found 

 a similar upper limit for Laurentian boulders at 3,400 feet.J These ob- 

 servations are cited here for purposes of comparison. 



In the report of 1882-'84 it was stated that a similar limit occurred on 

 the Rocky Spring ridge of northern Montana, 10 miles south of the bound- 

 ary line and 66 miles from the mountains, at 4,100 feet. The plateau only 

 slightly exceeds this height, and, while convinced of the accuracy of the 

 observation at the time, its wide discrepancy from other results may per- 

 haps be regarded as leaving it open to suspicion. I have not had an op- 

 portunity since of verifying it. 



Before dealing with the facts ascertained in 1894, it should be noted that 

 Mr McConnell had in 1890 carefully examined the sections of the glacial 

 deposits along Bow river between the mountains and Gleichen (about 80 



* In this and other cases, unless otherwise noted, distances from the mountains are measured at 

 right angles from the nearest part of the base of tlie range. 

 t Op. cit., p. 73 C. 

 X Annual Report, Geol. Survey of Canada, vol. ii (n. s.), p. 145 E. 



