PEMBINA MOUNTAIN. 41 



the international boundary. It is a prominent Avooded bluff, some 300 feet 

 high, extending in a ^-ery direct course from) south to north or a few 

 degrees west of north. From its southern end to the Pembina River the 

 base of this escarpment is 1,200 to 1,225 feet above the sea. The width 

 occupied by its slope varies from a half mile to 2 or 3 miles, and from 

 its crest a treeless plateau, having a moderately rolling surface, stretches 

 with slow ascent Avestward. North of the Pembina River its crest sinks to 

 about 1,400 feet, and its base to about 1,025 feet, at the international 

 boundary. 



Where the Pembina River cuts through this escarpment, entering the 

 area of Lake Agassiz, the eroded eastern front of its delta deposit fonns 

 another conspicuous l^luff, about 200 feet hig'h, falling in a steep, wooded 

 slo^je from 1,175 to 975 feet, approximately, above the sea-level. The 

 delta bluff", called the "First Pembina Mountain," is composed of sand and 

 gravel, and lies about 5 miles east of this more prolonged line of highland, 

 which is denominated in that vicinity the "Second Pembina Mountain." 

 The latter, throughout its entire extent both in North Dakota and Manitoba, 

 is caused by the outcrop of a continuous belt of almost level Cretaceous 

 strata, mostly overspread by glacial di'ift. 



The ascent of this highland on the international boimdarv, where it 

 occupies a width of about li miles, is described by Dr. G. M. Dawson as 

 follows : 



The eastern frout of Pembina escarpment is very distinctly tei-raced, and the 

 snmmit of the plateau, even at its eastern edge, thickly covered with drift. The first 

 or lowest terrace, which is about one-third from the i)rairie level toward the top of 

 the escarpment, does not seem to preserve exactly the .same altitude. On the boun- 

 dary line its height above the general prairie level was found to be about 90 feet, a 

 •second terrace 200 feet, and that of the third level, or summit of the plateau, about 

 300 feet. The surface of the first terrace, which is here wide, is strewn with bowlders, 

 as is also that of tlie second terrace and plateau above. These are chiefly of Lauren- 

 tian gneiss and granite, but a few smaller ones of limestone occur. The banks of 

 ravines cutting the top of the plateau and draining westward into the Pembina River 

 show in some places a great thickness of light-colored, yellowish, marly drift, with 

 few bowlders embedded in it.' 



' Report on the Geolojty and Resources of the Forty-ninth Parallel, from the Lake of the Woods to 

 the Rocky Mountains, 1875, p. 219. 



