312 Tertiary. 



tain corresponds with the Big ridge, and bej'ond it forms the limit of 

 a former extension of Lake Winnipeg. On the east side of Red river 

 the Big ridge is traced nearly due south from the Middle settlement 

 to where it crosses the Roseau, 46 miles from the mouth of that stream, 

 and on or near the 49th parallel. It is next met with at Pine creek, 

 in the State of Minnesota, and from this point it may be said to form 

 a continuous level gravel road, beautifully' arched and about 100 feet 

 broad, to the shores of Lake Winnipeg, 120 miles. On the west side of 

 Red river, north of the 49th parallel, and north of the Assiniboine, from 

 a point near Stony mountain, it extends to near Prairie Portage, where 

 it has been removed by the Prairie Portage river and the waters of 

 the Assiniboine. It may be seen again on White Mud river, about 

 20 miles west of Lake Manitobah. 



In the rear of Dauphin lake, the next ridge in ascending order 

 occurs; it forms an excellent pitching track for Indians on the east 

 flank of the Riding mountain. At Pembina mountain four distinct 

 steps or beaches occur, the summit of which is 210 feet above the 

 prairie. 



The lower prairies enclosed by the Big Ridge are everywhere inter- 

 sected by small subordinate ridges which often die out, and are evi- 

 dently the remains of shoals formed in the shallow bed of Lake Winni- 

 peg, when its waters were limited by the Big ridge. The long lines of 

 bowlders exposed in two parallel, horizontal rows, about 20 feet apart, 

 in the drift of the south branch of the Saskatchewan above mentioned, 

 are the records of former shallow lakes or seas in that region. 



They may represent a coast line, but more probably low ridges 

 formed under water, upon which bowlders were stranded. The fine 

 layers of stratified mud, easily split into thin leaves, which lie just 

 above them, show couclusivelj' that they were deposited in quiet water; 

 their horizontality proves that they occupied an ancient coast or ridge 

 below the comparatively tranquil water of a lake of limited extent; the 

 vast accumulations of sand and clay above them establish the antiquity 

 of the arrangement; and the occurrence of two such layers, parallel to 

 one another, and separated by a considerable accumulation of clay and 

 sand, leads to the inference that the conditions which established the 

 existence of one layer also prevailed during the arrangement of the 

 other. It may be that these are bowlders distributed over the level 

 fioor of a former lake or sea, and they may cover a vast area. 



The Pembina mountain is par excellence the ancient beach in the 

 valley of Lake Winnipeg. It is not a mountain, nor yet a hill. It is a 



