[keele] MESOZOIC clays AND SANDS 29 



Masses of yellow and orange sands covered by glacial drift occur 

 on Abitibi and Mattagami rivers. These sands are presumably of 

 Tertiary origin. 



There were at least two periods of glaciation over the region in 

 Pleistocene times. Remnants of inter-Glacial deposits are found at 

 intervals in the region, underlain by Palaeozoic rocks, but none are 

 found in the Pre-Cambrian upland. The grey till, a product of the 

 last glaciation, is spread everywhere and forms the surface of the 

 greater part of the region. 



Glaciation 



Glaciation has not only profoundly affected the Cretaceous 

 formation in northern Ontario, but has entirely changed the appear- 

 ance of the pre-Glacial land surface of the region. 



At the present day we catch glimpses onl}' of the ruins of the 

 Cretaceous formation at isolated spots on the river banks; and instead 

 of the uneven, rocky topography of pre-Glacial times we see a nearly 

 uniformly level surface underlain b^^ glacial drift. 



There were at least two distinct periods during which the land 

 surface was occupied by ice. In the interval between these periods 

 conditions favourable to erosion, weathering, leaching, deposition of 

 sediments, and plant growth, were restored. 



The inter-Glacial deposits which were then laid down suffered 

 severely from the subsequent glaciation, but the inter-Glacial remnants 

 are more numerous and much more imposing than are the vestiges of 

 the Cretaceous formation. The last glaciation moved from north 

 to south, carrying with it a huge cargo of till which was deposited in 

 a sheet not only over the Palaeozoic plain, but over the Pre-Cambrian 

 upland for a distance of 100 miles. 



This till is very bouldery in places, and is of a uniformly lead- 

 grey colour in the lower part, but the upper portion is weathered to a 

 yellowish grey. 



The banks of the rivers are almost entirely composed of this till, 

 and the beds of all the rivers are strewn with boulders derived from it. 

 The Cretaceous beds on Mattagami river are overlain by about 

 75 feet of the late glacial till. 



The till or boulder clay at the base of the inter-Glacial beds is 

 reddish in colour, and, although it contains a good deal of grit as well 

 as boulders, it also contains a fair percentage of plastic clay. The 

 red colour and plastic properties of this till may be due in part to its 

 derivation by erosion from the highly coloured clay beds of the 

 Cretaceous, or, as is more likelv, from erosion of the red Salina shales 



