SOME STRATIGRAPHIC AND STRUCTURAL FEATURES 

 OF THE PRE-CAMBRIAN OF NORTHERN QUEBEC 



H. C. COOKE 



PART III 

 CORRELATION 



In this region, where the sedimentary series do not form any 

 large or continuous sheet, but are found merely as comparatively 

 small remnants separated by wide areas of intrusive granite, it 

 is obviously impossible to make an unquestionable correlation. 

 If in some yet unexplored district there should be found large 

 continuous sheets of sediments which might serve as definite 

 horizon markers over a large area, as the Cobalt series does in the 

 Cobalt-Sudbury-Lake Huron district, a good correlation may even- 

 tually be obtained. But under present conditions the criteria 

 on which we must rely for correlation purposes are (i) petrogra- 

 phic similarities; (2) similar geological successions; (3) similar 

 deformations; (4) similar relations to older and younger forma- 

 tions. 



PONTIAC-MATTAGAMI-BROADBACK-BROCK SERIES 



The patches of sediments known at present under the local 

 names Pontiac, Mattagami, Broadback, and Brock series have 

 strong petrographical similarities. In each the principal rock is 

 a schist which is probably the metamorphosed equivalent of a 

 more or less impure sandstone or sandy shale. It is now com- 

 posed of quartz and ferromagnesian mineral, with a Httle feld- 

 spar; the ferromagnesian mineral is usually biotite, which locally 

 is replaced by muscovite or hornblende. The muscovite schist 

 probably represents an originally fairly pure sandstone, and the 

 hornblende schist a ferromagnesian sand. The more acid types 

 may have derived their material largely from granitic sources, 

 the more basic types from the basic lavas. The mica schists 



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