108 A. WINCHELL A LAST WORD WITH THE HURONIAN. 



eroiis [Keweenawan] series of the south shore of Lake Superior. As the 

 rocks above the break coutaiued native copper, he designated them the 

 " upper copper-bearing series." * This series was also manifestly divisible 

 into two parts — the lower consisting of "bluish slates or shales, interstrati- 

 fied with sandstones aud beds of columnar trap, and the upper of a succes- 

 sion of sandstones, limestones, indurated marls and conglomerates, also 

 iuterstratified with trap, which is often amygdaloidal " (p. 67). We may 

 speculate as to the motives which led to this arrangement. In the Huron 

 region had been seen, indeed, the upper and lower types of slate conglom- 

 erate ; but if their discordant structural relations had not been noted they 

 could easily have been regarded as members of one system. At Dore river, 

 on the east shore of Lake Superior, was a slate conglomerate, reproducing 

 perfectly characters seen north of Lake Huron, and therefore unhesitatingly 

 pronounced Huronian, and conceived as holding a geographical connection 

 {ante, p. 94) with the system north of Lake Huron, not yet suspected of 

 being duplex. At Thunder bay, north of Lake Superior, was a slate con- 

 glomerate of identical character {ante, p. 93) ; and having recognized that 

 as Huronian, the upper slate conglomerate there was of necessity excluded, 

 for there the discordance of stratification was glaring. Thus, since 1861, the 

 " Huronian " of the east, north and south shores of Lake Superior has been 

 understood as meaning the series of schists immediately succeeding the 

 gneisses. 



Views of Hunt and Lawson. — In 1873 Dr. Huntf applied the term "An- 

 imike " to the lower group of the " upper copper-bearing series " — later equated 

 with the Taconic — and the term "Keweenaw" (later "Keweenian") to the 

 upper group of that series ; while in 1866 Dr. Lawson applied the term 

 " Keewatin " to the so-called "Huronian" or " lower copper-bearing series" 

 of the north shore of Lake Superior. J 



Summary of Logan's Conception. — Sir William Logan's conception, there- 

 fore, of the taxonomic arrangement and equivalences of the Canadian rocks 

 about the Great Lakes, may be set forth in the table which follows : 



On Lake Superior. 

 Potsdam sandstone. ^ 



Unconformity. 



Upper Copper-bearing series i t ^ ^ ^ 

 ^ ^ ^ ^ ^ ( Lower group. 



Unconformity. 



Huronian, or Lower Copper-bearing series. 



Gneiss. 



On Lake Huron. 

 Potsdam sandstone. 

 Unconformity. 



Huronian. 

 Gneiss. 



*Gpology of Canada, 1863. chapter V. 



t Trans. Amer. Inst. Mining Eng., vol. I, p. 339. 



X Geological Survey of Canada, New ser., vol. I, Report for 1885, CC, pp. 10-15. 



