SUMMARIES OF PRE-CAMBRIAN LITERATURE OF 

 NORTH AMERICA 



EDWARD STEIDTMANN 

 University of Wisconsin 



II. ONTARIO 



In the region northeast of Lake Huron, the pre-Cambrian rocks 

 according to Collins and others show one conspicuous unconformity. 

 The rocks beneath this unconformity comprise a series of quartzites 

 and other clastic sediments, the Timiskaming series, etc., intruded 

 by granitic rocks. Unconformably beneath these sediments is an 

 older series, the Keewatin, including basic flows, some acid extru- 

 sives, iron formations, dolomites, etc. The Keewatin is intruded 

 by the Laurentian granites and gneisses. 



Above the conspicuous unconformity are two series of slightly 

 metamorphosed dominantly clastic sediments separated by an 

 inconspicuous unconformity. The lower one, the Bruce series, 

 locally contains tillites. The upper series is generally known as 

 the Cobalt series. At Killarney on the north shore of Lake Huron, 

 Collins has found that the Bruce and possibly the Cobalt series 

 are intruded by the Killarney granite and in this locality they 

 assume many of the characteristics of the older series, the Timis- 

 kaming. The youngest pre-Cambrian rocks are Keweenawan, 

 basic dikes and sills. 



Northwest of Lake Superior, Lawson has restudied the Rainy 

 Lake and Steeprock Lake districts. Greenstones and other rocks 

 typical of the Keewatin are widely exposed in this region. Beneath 

 them are acid schists called Coutchiching by Lawson. Uncon- 

 formably above the Keewatin in the vicinity of Rainy Lake are a 

 series of conglomerates and slates called the Seine series by Lawson. 

 In the Steeprock Lake district, the Steeprock Lake series lies 

 unconformably between the Keewatin and Seine series. The 

 Steeprock Lake series, besides clastic sediments, comprises fossil- 

 bearing dolomites. 



643 



