30 THE ROYAL SOCIETY OF CANADA 



of the Silurian which form part of the bedrock in the region near 

 James Bay. 



No inter-Glacial beds have been found on the Pre-Cambrian 

 upland, but a pre-Glacial valley on the east side of Missinaibi river, 

 just below the end of Long Portage, is filled with a very dark coloured, 

 stratified, peaty clay deposit, which is undoubtedly of inter-Glacial 

 age and bears a strong resemblance to the Toronto formation^ in the 

 inter-Glacial beds at Toronto, Ontario. 



Tertiary Erosion and Deposition 



It is probable that the Cretaceous deposits were uplifted and 

 wasted by stream erosion and weathering during Tertiary times. 

 It is not definitely known that any Tertiary deposits occur in the 

 region, but certain beds of yellow and orange sands on Mattagami 

 and Abitibi rivers are probably pre-Glacial in origin and may be 

 Tertiary. The most extensive yellow sand deposit on Mattagami 

 river occupies about a quarter of a mile of the east bank, between the 

 mouth of Pike creek and the iron ore deposit at the head of Grand 

 Rapids. 



These sands extend below water level and vary in thickness from 

 10 to 25 feet. «They are overlain by only a foot or two of stratified 

 silts from which they are separated by a thin layer of rusty pebbles. 

 The sands are composed entirely of coarse quartz grains often with a 

 cross-bedded arrangement interbanded occasionally with streaks of 

 pea-sized gravel composed mostly of quartz, although pebbles of the 

 harder parts of pre-Cambrian rocks are also present. Occasionally 

 pockets and streaks of micaceous clay are included, as well as rusty 

 and disintegrated cobble stones. 



The materials are coarser at the northern end of the deposit, 

 where they finally pass into yellow gravels with pebbles of cobble 

 stone size, and end abruptly against boulder clay. 



The sands are compact enough to retain a fairly vertical face, 

 but there are no cemented beds. 



The colour of the beds varies from yellow to orange and reddish 

 brown, and appears to be mainly due to a coating on the quartz 

 grains and not to fine material intermixed with the sands. 



A similar deposit on the opposite bank of the river evidently 

 formed part of the beds above referred to before the river cut through 

 them. 



1 Inter-Glacial Period in Canada, Compte-Rendu, Cong. Geol. Intern., Mexico, 

 1906. 



