SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 475 



The ore body contains pockets of pyritic sand which have become 

 more numerous with depth. 



Wilson^ reports on a reconnaissance survey of the area to the 

 north of Lac Seul and east of Trout Lake in the Northwest Terri- 

 tories of Canada. He found only pre-Cambrian rocks, of which 

 the oldest are chiefly hornblende schists and amphibolites. The 

 greater portion of the area is underlaid by granites and gneisses 

 intrusive into the basic rocks. 



Wilson^ finds that the pre-Cambrian rocks of the Algoma and 

 Thunder Bay districts between 48° 30' and 51° north latitude, and 

 84° and 87° 30' west longitude, include Laurentian granite and 

 gneiss with some hornblende schists, biotite schist, and diabase 

 which may be Keewatin. 



Wilson^ states that the pre-Cambrian succession in the Nipigon 

 river basin is as follows : 

 Keweenawan 



Diabase intrusives 



Dolomitic limestone 



Shale 



Sandstone 



Unconformity 

 Lower Huronian 



Small bands of conglomeratic arkose and slate 



Unconformity 

 Laurentian 



Granites and gneisses intrusive into Keewatin 

 Keewatin 



Greenstone and greenstone schists infolded with jaspilitic iron formation 



Wilson'' reports the following pre-Cambrian succession from the 

 region about Larder Lake, Ontario and eastward : 

 Post Huronian 



Diabase, gabbro, porphyry, and lamprophyre 



Igneous contact 



^ A. W. G. Wilson, "Lac Seul to Cat Lake," Canada Geol. Survey, 1909, 23 pp. 

 ^ M. E. Wilson, "Geological Reconnaissance of a Portion of Algoma and Thunder 

 Bay Districts, Ontario," Canada Geol. Surv., 1909, 49 pis., 6 pis. 



3 A. W. G. Wilson, "Geology of the Nipigon Basin, Ont.," Canada Geol. Surv. 

 Mem. No. i, 1910, 152 pp., 16 pis., 4 figs., i map. 



4 M. E. Wilson," Larder Lake and Eastward," Canada Geol. Surv., Summary RepL, 

 1909, pp. 173-79, iQio- 



