66 H. C. COOKE 



volcanics, which form the basal rocks of the region; (2) the exist- 

 ence of a thick sedimentary series, the Nemenjish series, which Hes, 

 so far as results at hand indicate, conformably on the surface of the 

 lavas, and which appears to correspond to the Grenville series; 

 (3) the occurrence of a second sedimentary series, the Mattagami 

 series, in scattered patches unconformably on the surface of the 

 older lavas and sediments. All of the rocks mentioned are older 

 than the Cobalt series of the Timiskaming district, and are probably 

 of pre-Huronian age, using the term "Huronian" as defined by the 

 International Committee. The basal series of lavas may be of the 

 same age as the Keewatin of the south shore of Lake Superior. 

 The younger series of sediments (Mattagami) appears to occupy a 

 new position in the geologic column, hitherto unfilled, between the 

 Keewatin and the Lower Huronian of the International Committee's 

 classification. 



The region approximates in shape a rectangle 270 miles from 

 north to south, and 350 miles from east to west (Fig. i). Since 1908, 

 the western third of it has been studied in considerable detail by 

 M. E. Wilson, J. A. Bancroft, and T. L. Tanton; the greater part of 

 the remainder has been rapidly examined by reconnaissance methods 

 by the writer. In addition, the Chibougamau Mining Commission 

 has examined a limited area around Lake Chibougamau in detail, 

 and J. A. Dresser has similarly studied an area around the south 

 end of Lake St. John. The northern Quebec region connects on 

 the southwest with the Cobalt-Sudbury-Lake Huron region, which 

 has been mapped in detail by Miller and Knight and W. H. Collins, 

 so that a correlation of the whole Lake Huron-Cobalt-northern 

 Quebec region presumably may be attempted in the near future. 



This paper is merely a preliminary attempt to piece together 

 some of the fragments of the pre-Cambrian record. The reader 

 should remember the difficulties of deciphering this record, since 

 the areas of ancient rocks are frequently small and disconnected, 

 and the rocks themselves have commonly been sheared and 

 recrystallized. As work is carried over larger areas and the 

 number of facts for piecing out the record becomes greater, many 

 of the conclusions stated in this paper will undoubtedly be modified 

 or discarded. The writer considers, however, that such a concrete 



