n6 The Ottawa Naturalist. [August 



To the east is a rug-ged plain sloping gently westward. On 

 this many small lake-basins are seen and the streams winding 

 through it are peculiar in that they have not of themselves worn 

 down valleys but are found winding in various ways seeking the 

 lowest level, passing through lake expansions which are merely 

 hollows hlled to the level of the lowest outlet. This area is a part 

 of the original continent formed after the molten mass of the earth 

 had cooled sufficiently to have formed upon it a crust. 



A study of this area shows that the original crust suffered 

 many changes — that successive sinkings into the still molten mat- 

 ter beneath, modified much of it or probably remelted all of the 

 original surface. The earliest littoral deposits are associated with 

 eruptive greenstones, and wherever remnants of these are found 

 they are nearly always surrounded by rocks which appear to have 

 been at a later date in a plastic condition and to have enfolded the 

 early sedimentaries. These remnants are of great economic value 

 inasmuch as they have been specially enriched by veins carrying 

 the precious and other metals and minerals. A long lapse of time 

 enabled the surface to become firmer before additional deposits 

 were placed upon it, but the surface suffered great denudation and 

 a large part of it was removed to form the earlier stratified sea 

 deposits. The uneven nature of its present surface is due in a 

 great measure to the varying hardness or brittleness of the con- 

 stituent rocks. 



The country beneath this rough slope and the edge of the 

 plateau to the west of the valley is underlain by limestones placed 

 nearly horizontal and covered by coatings of clay, the nature of 

 which is dependent on the conditions of deposition. 



The plateau to the west through which may be seen many deep 

 river channels is composed of a series of soft, dark coloured, easily 

 eroded shales or hardened clays with occasional overlying deposits 

 of sand and clays of a lighter colour containing a few seams of 

 lignite which were deposited in shallow, probably brackish water. 



These various deposits indicate a certain part of the history 

 of the continent to be briefly as follows : — 



A subsidence of the original continent brought the sea into the 

 central part of the present land area, so that its waters covered 

 perhaps all of Manitoba. The advance was slow and represents a 



