﻿PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Apr. 10, 



banks become bigh. At tbe Eat Portage, tbis terrace, which is 150 

 feet above Lake Winnipeg, retires from tbe river on eacb side, and 

 is replaced by another at an altitude of only 75 feet, tbrougb a cut- 

 ting in wbicb tbe river flows to its moutb at Fort Alexander. Tbis 

 ancient lake-bottom extends soutb of tbe 49th parallel into the 

 American State of Minnesota, and everywhere presents a rich level 

 prairie, only broken by slight gravel-ridges which have formed 

 shoals in tbe ancient lake, or by patches of the magnesian lime- 

 stone beds which crop out into the plain, such as at the Stony 

 Hills, east of Fort Garry, which must have been a rocky island at 

 one time. 



The banks of the lower part of Rainy River are composed of rich 

 alluvial deposit of a bight-grey colour, containing a large proportion 

 of white sand. It is distinctly stratified, and has without doubt 

 been formed by an extension of tbe Lake of the Woods back towards 

 Rainy Lake. In the upper part of Rainy River, the banks are high 

 and terraced, and boulders show that at this level there is also a 

 deposit of true Drift. 



At Pembina Mountain, the eastern limit of the Second Prairie- 

 level forms an escarpment measuring 250 feet above the plain at its 

 base. From the point where it crosses tbe 49th parallel, it sweeps 

 to the north-west and assumes a more gentle slope, being broken up 

 into three or four subsidiary terraces. It then meets the Assine- 

 boine River near the mouth of the Souri, and is continued to tbe north 

 by the high grounds that lie to the west of Manitoba Lake from Riding 

 Mount to the Basquia Hills, which, however, rise to tbe full height 

 of the level — that is, to 1600 feet above the sea. Below Fort a la 

 Corne the banks of tbe Saskatchewan are described as suddenly be- 

 coming reduced from tbe height of several hundred feet to a slight 

 elevation above tbe river, showing that it is at that place where the 

 eastern limit of this level meets that river. Tbe prairies of the 

 Upper Assineboine, the Qu'appelle River, and those along the Sas- 

 katchewan, from Fort a la Corne to the elbow on the south branch, 

 and also up as far as the longitude of Fort Pitt on the north branch, 

 all belong to tbis level, which also extends to the base of the Great 

 Missouri Coteau. The mineral composition of the superficial de- 

 posits of the Second great Prairie-level is very different from 

 that of the first. Sand is the predominating ingredient. Thus at 

 St. Joseph, where the banks of tbe Pembina River present a fine 

 section of it to its base, the material is a coarse red sand, with 

 gravel and boulders. There are no signs of stratification in any 

 part of this deposit as seen at Pembina Mount, but further west, 

 where it assumes a light-grey colour, and contains a considerable 

 quantity of lime, it is imperfectly bedded, Near Fort Ellice, and 

 at many other parts of the district to the south and west of that 

 place, this deposit is formed wholly of fragments of the under- 

 lying Cretaceous shales. At Long River, Forked Creek, and many 

 other places, this deposit was observed to form only a very thin 

 coating to the Cretaceous rocks. Notwithstanding that the prai- 

 ries of tbis level are often cut to a great depth by the rivers and 



