650 EDWARD STEIDTMANN 



series, consists of a thin basal conglomerate, white quartzites 

 with interbedded, well-sorted conglomerates, an impure siliceous 

 limestone, and some graywacke, whose maximum thickness is 

 more than three thousand feet. The upper division, or Cobalt 

 series, includes tillites, quartzites, graywackes, a few thin im- 

 pure Kmestone beds and grades upward into pure quartzites. 

 It has in part the characteristics of glacial till associated with 

 stream and quiet-water deposits contemporaneous with glaciation. 

 Locally it shows minor unconformities. The local terms, Bruce 

 and Cobalt series, rather than Lower Huronian and Upper Huron- 

 ian, are applied to these divisions because their full equivalence to 

 these units in the original Huronian is regarded as doubtful. 



Collins^ advocates that a local classification of the pre-Cambrian 

 rocks of the Timiskaming region be adopted and that their correla- 

 tion with other districts be postponed until they are better known. 

 He emphasizes the importance of the unconformity at the base of 

 the Cobalt series as major plane of division. The various series 

 are classified by him as pre-Huronian and Huronian. His classi- 

 fication follows : 



XT / Diabase 



^^^^^"^^^^1 Sudbury norite 

 Intrusive contact 



Whitewater series \ Huronian 



Lorrain series 



Local unconformity 

 Cobalt series 



Great unconformity 

 Batholithic granite intrusive 



Intrusive contact 

 Sudbury, Timiskaming, Fabre series t p^e-Huronian 



Unconformity 

 Granite intrusives 

 Keewatin group 



Collins^ reports that hitherto unknown granites intrude the 

 Bruce and probably the Cobalt series along the coast of Lake 

 Huron. 



' W. H. Collins, "A Classification of the Pre-Cambrian Formations in the Region 

 East of Lake Superior," Congres Geologique International XII. Session 1914, 

 pp. 399-407- 



^W. H. Collins, "The Age of the Killarney Granite (Ontario)," Canada Geol. 

 Surv. Mus. Bull. No. 22 (1916), 12 pp., i pi., i fig. 



