32 



THE ROYAL SOCIETY OF CANADA 



The non-Glacial character of these sands indicates that they have 

 been formed from debris carried by streams from the pre-Cambrian 

 upland and deposited as deltas on the Palaeozoic plain. 



It is probable that a long period of weathering caused the accumu- 

 lation of a considerable amount of coarse disintegrated rock material 

 as well as clay, the transport of the coarser materials having been 

 made possible by an uplift of the land surface in late Tertiary tmies 

 which would increase the carrying power of the streams. 



The scouring of the residual mantle from the pre-Cambnan 

 upland appears to have been fairly complete before glaciation set in. 

 There is very little true boulder clay in the glacial drift upon the pre- 

 Cambrian surfaces except on parts so situated that the ice had previ- 

 ously passed over adjacent Palaeozoic rocks. When the supply of 

 clay collected from the Palaeozoic rocks had been deposited and the 

 ice had extended over the pre-Cambrian surfaces there was apparently 

 no more clay to be obtained. 



The purely pre-Cambrian drift is a thin sheet, consistmg mostly 

 of silt, sand, gravel, and stones, including a surprisingly small amount 

 of real clay substance. 



Character and Thickness of the Cretaceous Deposits 



The Cretaceous deposits in northern Ontario occur in isolated 

 outcrops at certain points on Missinaibi and Mattagami rivers, north 

 of the pre-Cambrian rock boundary. 



The deposits consist of white sands; pink, white, yellow, black 

 and grey to almost black clays; and lignite. 



Few of the outcrops seen above water level along the river banks 

 give a clue to the character of the deposits, and it is mainly from 

 borings that the information is obtained. 



The first borings were made in 1890 by Mr. Boiron at the lignite 

 outcrop on Coal brook. The following record, selected from his list 

 of borings, illustrates the character of the materials found at this 

 point, from the surface downwards: 



Drab and variegated clays. • 5 feet 



Black carbonaceous clays and lignite 7 



Drab clay. ^ 



Black clay and lignite 1 foot 



Variegated clays : • • • ^ feet 



Sandy clay ^ 



Lignite 



