TAXONOMY OF GREAT LAKE ROCKS. 109 



Views of the Author. — On the contrary, the succession and synchronism 

 contended for in the present paper are set forth as follows : 



On Lake Superior. 

 Potsdam sandstone. 



Unconformity. 

 Keweenian* (Upper group, Upper Copper- 

 bearing series). 

 Aniraike or Huronian (Lower group, Upper 

 Copper-bearing series). 



Unconformity. 

 Kewatian f (Lower Copper-bearing series). 

 Gneiss. 



On Lake Huron. 

 Potsdam sandstone. 

 Unconformity. 

 (Keweenian not known.) 



Huronian, upper. 



Unconformity. 

 Pseudo-Huronian. 

 Gneiss. 



UNION OF TWO SYSTEMS IN MINNESOTA AND THE NORTHWEST. 



Views of Logan and others. — It is well known that the Animike slates con- 

 tinue south westward as far as Pigeon river.J From Pigeon point westward 

 they have been traced by Irving and N. H. Winchell as far as Grand Port- 

 age on the international boundary ; and by the geologists of the Minnesota 

 and National surveys as far as Gunfliut lake, on the boundary.§ Between 

 the vicinity of Thunder bay and Gunflint lake the older and vertically 

 standing schists are entirely concealed, so far as the writer is informed, ex- 

 cept at one locality near North Fowl lake.|| On the north side of Gun- 

 flint lake the vertical Kewatian schists emerge from beneath the Animike 

 in a discordant outcrop which has been frequently described by the writer. 

 The Animike has been traced in unbroken continuity still further westward 

 to the vicinity of Ogishke-muncie lake, and, with interruptions, as far west 

 as Daluth. Throughout this whole extent no one has ever suggested that 

 the formation is not the same as occurs on Thunder bay, where Irving iden- 

 tified it with the Huronian of Lake Huron — meaning, as we understand 

 him, the upper Huronian of Lake Huron, with which meaning we are en- 

 tirely in accord. But from the vicinity of Ogishke-muncie lake, the vertical 

 Kewatian system of rocks has been many times traced, without interrup- 

 tion, to Vermilion lake, where it embraces conformably the great iron-ore 



*This group is thought by Irving unconformable with the Aninniiie ("Copper-bearing Rocks of 

 Lake Superior," 1883, pp. 157,385,405,416-7). Hunt thinks the assunned upper beds (Nipigon group) 

 distinct and unconformable (Min. Physiology and Physiography, 1880, p. 578 ; Azoic Kocks, 1878, 

 pp. 24U, 241), but Irving finds them beneath tlie Animike (ib., p. 157). 



t A homophoDous adaptation of " Keewatin " of Lawson. 



t Logan, Geology of Canada, 1863, p. 77 ; Kell, Report Geol. Surv. of Canada for 1866-9, p. 322. 



gSee the writer's memoir in Bull. Geol. Soe. Amer., vol. I, 1890, pp. 385-90. 



II Sixteenth Annual Report Minnesota Survey, 1887, pp. 284, 338. 



XVII— Bull. Geol. Soc. Am., Vol. 2, 1890. 



