BOWLDERS PERCHED ON AN ESCARPMENT. 305 



derived. These blocks are generally more angular than those from a simi- 

 lar source found at lower levels, and are associated with many others of local 

 origin." 



In approaching the base of the Niagara escarpment anywhere from Lake 

 Ontario to Georgian bay, or along its continuation to the northwestward 

 through the Indian peninsula and the Manitoulin islands, one cannot fail to 

 remark the absence of any considerable talus or accumulation of the waste 

 of the former extension of the strata composing the cliff. The fallen blocks, 

 except the most recent ones, have all disappeared, and we find them perched 

 up on the brink or scattered on the plateau above it, instead of strewn over 

 the lower lands at its foot, where we might have naturally looked for them. 

 On the west side of Lakes Manitoba and Winnipegosis an east-facing escarp- 

 ment of nearly horizontal Cretaceous strata rises to a height of about a thou- 

 sand feet in the form of the Riding and Duck mountains. The table-land 

 of these mountains is, in many parts, strewn with Laurentian bowlders de- 

 rived from the lower-lying Archean region east and northeast of Lake Win- 

 nipeg, showing a great uplifting of the erratics by the glacier-sheet. The 

 bowlders are occasionally deposited in ridges and hummocks, some of which 

 are mentioned in my report for 1874. 



In the report for 1873 on the Northwest Territory, I showed that the drift 

 of the country between the Laurentian region and the Coteau de Missouri 

 came from the northeastward, and that it consists of " Laurentian gneiss, 

 granite, syenite, and the crystalline schists of the Huronian series, together 

 with a large proportion of compact, buff, drab, and gray limestone;" also 

 that the front of the Coteau itself " consists in reality of the ruins of an 

 escarpment;" aud that "the force which had undermined it had evidently 

 acted from the northeastward." The high ground of the Coteau was fur- 

 ther described as very rough and covered with the above kind of drift. 

 Many of the Laurentian bowlders are angular, and they "are so numerous 

 over considerable areas that a man might walk upon them in any direction 

 without touching the ground." * The front of the Coteau was ascertained 

 by barometer to rise from (300 to 700 feet above the plain immediately to 

 the north of it. The hills of drift above the Coteau are steep and gener- 

 ally conical, and resemble, on a grand scale, the appearance of stiff stony 

 earth newly dumped in separate piles close together. The hollows between 

 these hills contain numerous ponds and small lakes. As the foot of the 

 Coteau is probably as high as the average of the Laurentian surface to 

 the northeast, if not higher, the ice-sheet must have been able to elevate this 

 vast quantity of drift to the above heights. 



The angular character of many of the bowlders which have been raised 

 to the various elevated areas just described is an interesting tact, and it 



* Rep. of Progress Geol. Surv. Can. for 1873, 1874-75, page 43. 



