MICHIGAN ACADEMY OF SCIENCE. 43 



ON THE GLACIAL ORIGIX OF HrROXTAX ROCKS OF NIPIS- 



SIXG, OXTARIO. 



REGINALD E. HORE. 



In the eariv (184G et scq.) reports of the Canadian Geological ^^llr- 

 vey there appear descri])tions bv ^sir Wni. Logan of a series of non- 

 fossiliferous clastic rocks found on the west shore of Luke Teniiskaming 

 and north of Lake Huron. Logan correlated the rocks of the two 

 localities and gave them the name Huronian. He believed them to be 

 younger than, and made uji jiartly of detritus from, the Laurentian, 

 a.nd his conclusions have been verified by later observers. 



Recently these rocks have attracted mor^e than local interest on ac- 

 count of the discovery of rich silver veins at Cobalt. In six years this 

 camp has yielded sixty-three million ounces of silver at a net profit 

 of seventeen million dollars, and it is expected that the production 

 of the coming year will be greater than that of any previous. 



As a result of their economic importance the rocks have been sub- 

 ject to much closer examination than before, and many interesting 

 features have been noted. Among these are j)eculiar characters which 

 are strongly suggestive of the existence of glaciers in Xipissing in early 

 Huronian times. 



Dr. A. P. Coleman^ who has made a study of these rocks from the 

 stand point of the glacialist, has gathered evidence from which he 

 concludes that there is no doubt of the glai-ial origin of the basal con- 

 glomerate of the lower Huronian. 



If is purposed here to present some facts which be<ir on this question. 



As will ap])ear from the accompanying table the chief rocks in this 

 district are of the Archean and Algonkian groups. These are separated 

 by a very marked unconformity and the interval was doubtless the great- 

 est which occurred in I're Cambrian times. There is no good reason 

 to dotibt that for a long jieriod of time the Archean rocks were being 

 worn down by all or any of the erosive agents now active. 



The Huronian series doubtless represent a portion of the secondary 

 rocks thus formed, and they are entirely composed of detrital material. 

 They are conveniently grouped into an upper and a lower series wliich 

 are generally conformable but in some localities separated by a slight 

 unconformity. 



The upper series is made up largely of medium grained feldspathic 

 quartzite with a little conglomerate material. It presents no unusual 

 feature and doubtless represents the hardened accumulation of a felds- 

 ]>athic sand derived from siliceous holocrystalline igneous rocks of the 

 Laurentian group. 



The lower series is made up largely of conglomerate, shale, grey- 

 wacke, and feldspathic quartzite. In many cases there is gradual grada- 

 tion vertically from one of these t^'pes to another. Less often there 



'The Lower Huronian Ice Age. ,7our. Geol.. Vol. XVI. llMtS, pp. 14".*-1.'.8. 



