GEOLOGY OF STEEPROCK LAKE. 11 



part. From the foregoing statements, we arrive at the probable 



position of the Steeprock series in the geological scale; and this 



may conveniently be presented in the form of a tabulation in 



chronological sequence : —  



^10 Keweenawan. 

 Algonkian ..,...-[ Erosion internal. 



I 9 Anin.ikie. 



EPARCHEAN INTERVAL. 



f 8 Granite gneiss, intrusive in the Seine series. 



Imiptive contact. 

 I 7 Seine series. 



j 6 Acute deforifiation and eiosion interval. 

 ArhiPan J 5 Steeprock series. 



^-"'^'*" ^ 4 ^ Erosion interval. 



3 Granite gneiss, intrusive in the Keewatiti. 

 Irruptive contact. 

 I 2 Keewatin. 

 L 1 Coutchiohing. 



The position of the Steeprock series, well down in the 

 Arclisean, is of interest from a general point of view, since, as will 

 appear in the sequel, the limestone of which it is chiefly composed 

 is fossiliferous. The fossils appear to be the oldest forms of life as 

 yet discovered. 



Before proceeding with the statement of the observations which 

 necessitate a change in the interpretation of the geology of Steep- 

 rock lake, it may be said that the exposure of the rocks about the 

 lake is probably much better than it was at the time of Smyth's 

 visit in 1891. The region has been extensively, and in places very 

 thoroughly denuded of its forests by fires, so that one may waU^ 

 inland from the shores of the lake at many localities over bare 

 glaciated rock surfaces. Smyth's observations were confined to the 

 shores of the lake, and his mapped distribution of the formations 

 away from there was conjectural, as was generally the case with 

 maps made at that period in the Archaean terraues of western 

 Ontario. His observations as to the extent and distribution of the 

 two most important members of the Steeprock series : I, the basal 

 conglomerate, and, II, the limestone about the shores of the lake, 

 appear to have been most careful and accurate. The only modifica- 

 tion which I was able to make in his mapping of these formations 

 on the actual shore line was the extension of the conglomerate (I) 

 to the main shore on the northeast side of Northwest bay. I also 

 found no evidence of the fault which he places through Birch point. 

 Inland from the lake shore, however, I found the distribution 

 of th& rocks in certain localities, which are decisive for the inter- 

 pretation of the structure, to be otherwise than Smyth had con- 



16279—3 



