284 G. M. DAWSON- ON THE SUPEKEICIAL GEOLOGY OE 



plateau of British Columbia ; but this will not explain the great 

 height to which water-action has extended on the east side of the 

 Eocky Mountains*, which was probably synchronous. The last 

 stage of the glacial period in the northern part of British Columbia 

 appears to have given rise to the silts of the Lower Nechacco basin, 

 while on the opposite side of the Eocky Mountains similar deposits 

 were laid down over the Peace-River country, the elevation of the 

 two districts being nearly alike. 



The general question of the origin of the drift-deposits of the 

 Great Plains having been fully discussed elsewhere f, it will be 

 unnecessary here to enter into it at length. The most remarkable 

 feature of the glacial deposits of the plains is the Missouri Coteau, 

 which it was supposed ran northward from the region near the 49 th 

 parallel, where it w r as more particularly studied, nearly following 

 the margin o£ the third prairie steppe. This supposition has since 

 been in great measure confirmed ; and on the journey from Edmonton 

 to "Winnipeg, in the autumn of 1879, I was able to examine cur- 

 sorily the character of this feature where it touches the north 

 Saskatchewan near the "Elbow," and to observe the great accumu- 

 lation of heavy boulders of eastern and northern origin in that 

 vicinity. Further north, the facts now advanced show that with 

 the general lowering of the surface of the country the well-defined 

 zone of drift-deposits known as the Coteau is more or less completely 

 lost, the material being scattered broadcast over the upper parts of 

 the basins of the Peace and Athabasca rivers, and approaching in 

 considerable mass the highlands near the base of the Eock}- Moun- 

 tains. 



Over the whole western portion of the plains, from the 49tli to 

 the 56th parallels, there is a mingling of the eastern and northern 

 Laurentian debris with that from the Eocky Mountains to the 

 west, the latter consisting largely of certain hard quartzite rocks, 

 and the overlap seeming to imply the existence of a sea in which 

 ice derived from both sources floated freely. 



Discussion. 



The Peesident spoke of the care with which Dr. Dawson con- 

 ducted his researches, and the value of his observations. 



Mr. Batjerman stated that he was not acquainted with the district 

 described by Dr. Dawson ; but he thought, from what he had seen 

 in Oregon and the Columbia valley, that many of the conclusions of 

 Dr. Dawson could be established. He, however, doubted whether 

 the ice had been quite so widely spread as Dr. Dawson supposed. 

 He described some of the great terraces on the Barrier Eiver ; there 

 were sixteen, one over the other, on a stupendous scale. He had 

 traced them on the Columbia Eiver to 2300 feet above sea-level ; 



* Quart. Journ. G-eol. Soc. vol. xxxi. p. 618. 



t Quart. Journ. G-eol. Soc. vol. xxxi. p. 603. ' Greology and Resources of the 

 49th Parallel,' p. 6. 



