Archean 



P RE-CAM BRIAN LITERATURE OF NORTH AMERICA 655 



Lawson' classifies the pre-Cambrian rocks of Steeprock Lake, 

 Ontario, as follows: 



Algonkian Keweenawan 



Erosion interval 

 Animikie 



Eparchean interval 

 Granite gneiss, intrusive in the Seine series 



Irruptive contact 

 Seine series 



Acute deformation and erosion interval 

 Steeprock series 



Erosion interval 

 Granite gneiss, intrusive in the Keewatin 



Irruptive contact 

 Keewatin 

 Coutchiching 



The Steeprock series comprise interbedded sediments and 

 irruptive rocks: dark-gray slate, agglomerate, greenstones and 

 green schists, conglomerates, and limestone. Van Hise and Leith 

 have correlated them as Lower Huronian. 



Lawson describes certain radial calcareous and siliceous fossil 

 structures of the limestones. The rays of these fossils extend to a 

 roughly circular limit in section normal to the axis of the organism. 

 In oblique sections, the border is usually elliptical. In some cases, 

 they are cornucopia-shaped, the rays sometimes showing conical 

 or elliptical septa. The rays vary from one to fifteen inches in 

 length. 



The paper is supplemented by descriptive notes on the fossils 

 by W. D. Walcott. 



Miller and Knight- discuss the metallogenetic epochs of Ontario. 

 Most of the metal production comes from Keweenawan rocks and 

 consists chiefly of silver, nickel, and copper in the order named. 

 Next in importance are the Algoman gold-bearing granite intru- 

 sions which have been productive at Porcupine and many other 

 places. The Keewatin has furnished a small tonnage of iron ore. 



^ A. C. Lawson, "The Geology of Steeprock Lake, Ontario," Canada Depl. oj 

 Mines, Mem. No. 2S (191 2), 23 pp., 2 pis. 



2 W. G. Miller and C. W. Knight, "Metallogenetic Epochs m the Pre-Cambrian 

 of Ontario," Ontario Bur. Mines, Ann. Kept., Vol. XXIV (1915), Part I, pp. 244-48, 

 map; Roy. Soc. Canada Trans., 3d Ser., Vol. IX (December, 1915), Section IV, 

 pp. 241-49, I fig. (map). 



