612 G. 2£. DAWSON OK THE SUPERFICIAL GEOLOGY OF 



Cretaceous clay or shale. Of the drift the lower portion is composed 

 of stratified sands and gravels, which are evidently false-bedded. The 

 pebbles are chiefly of the underlying rock, which, though soon split- 

 ting up under subaerial influences, has been hard enough to bear 

 rounding under water. There are also a few samples of rocks of 

 foreign origin, and the whole arranged in a manner implying a very 

 strong flow of currents in different directions. About 11 feet from 

 the top of the bank the false-bedded layers end abruptly, being cut 

 off by a well-marked horizontal plane. Above this the bedding is 

 nearly horizontal, and the drift includes many travelled boulders of 

 Laurentian and white limestone, some of them large, together with 

 much small Cretaceous stuff. Large boulders are also abundant, 

 protruding from the surface of the prairie above. 



In other places similar hard yellowish sandy clays are met with, 

 but with little sign of stratification, holding many well glaciated 

 stones, and thus resembling true till or boulder-clay. I do not think 

 that the boulder-clay and more perfectly stratified materials are here 

 essentially distinct ; but, as they were never seen in the same section, 

 I cannot speak positively on this point. In order to ascertain as far 

 as possible the origin of the foreign material of the drift and the 

 relative proportions of the different constituents, I adopted the follow- 

 ing method : — An average collection of pebbles taken at random from 

 the gravel of any locality was made, stones above or below a certain size 

 being rejected for convenience, and care being taken, where possible, 

 to combine gatherings from two or three spots for each locality,, and 

 to make the collection a large one. The pebbles so obtained were 

 then carefully enumerated and divided lithologically into groups, 

 which were referred as far as possible to their formations. From 

 the numbers thus obtained percentage ratios have been calculated. 

 The comparative simplicity of the geological features of the in- 

 terior of the continent, the similarity of the lithological characters 

 of the formations over great areas, and the absence of harder 

 metamorphic rocks in the strata of the plains are specially 

 favourable to such an investigation ; and the results serve to show 

 the general course of the drift in a region where rock-surfaces 

 capable of preserving glacial striae are entirely absent. It was at 

 first intended to enumerate the boulders and larger erratics in this 

 way ; but the criterion of smaller pebbles was found more frequently 

 applicable ; and wherever comparison was possible, the result ob- 

 tained from them appeared to agree closely with the proportional 

 importance of the larger masses. I shall present here only the 

 general average deduced from the second prairie-steppe as a whole, 

 which is as follows : — 



Laurentian 28*49 



Huronian 9-71 



Limestone 54*01 



Quartzite Drift 1*14 



The Laurentian material, consisting of granites and gneisses, is 

 easily distinguishable. Those Classed as Huronian are chiefly hard. 



