450 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 11, 



the glacial striations is about north and south ; and the drift occasion- 

 ally contains Upper Silurian fossils, which have been derived from 

 the country between the north shore of Lake Superior and Hudson's 

 Bay. 



Prom the preceding remarks on the nature of the surface, it may 

 be understood that the order of sequence of the rocks is not as yet quite 

 conclusively determined, and that therefore there may be some doubt 

 as to the proper age to be assigned to them, fossils being absent on 

 Keweenau Point. Where the rocks are bare, the section has been 

 well made from shore to shore by Mr. W. H. Stevens ; and they are 

 shown to be in conformable sequence from east to west. At Portage 

 Lake the lower boundary of the trap is hidden; and, indeed, researches 

 subsequent to those of Messrs. Poster and Whitney have shown 

 that more ground is included within the trappean range than is laid 

 down on their map. In the original survey of Messrs. Foster and 

 Whitney, these beds were assigned to the Potsdam or Lowest Silurian 

 group ; but subsequent investigations have led Prof. Hall and Sir 

 W. E. Logan to refer them to a somewhat higher level, or in the 

 Quebec group — the former geologist having determined that the 

 mass of the sandstones of the Sault S. Marie and the south-eastern 

 shore of the lake are equivalent to the Saint Peter's sandstones of 

 Minnesota, forming probably part of the Chazy formation*. On the 

 Canadian side of the lake, the traps are penetrated by intrusive 

 dykes which do not aifect the overlying sandstones ; but there is no 

 good evidence of asimilar unconformity in the upper beds of Keweenau 

 Point, as no transverse dykes are seen. I have examined the junction 

 of the traps and sandstones at three different points — namely, at Port- 

 age Lake, Copper Harbour, and Eagle River. In the latter case the 

 junction-surface was perfectly smooth, without any indication of 

 intrusion ; while in the two former a few small irregular veins, filled 

 with a red jaspery substance, are given oJff from the traps, and 

 penetrate the sandstones and conglomerates to the depth of a few 

 inches ; but this evidence is too inconsiderable to have much weight, 

 in view of the abundant proofs of conformable stratification derived 

 from the regular alternation of the conglomerates with the igneous 

 rocks. 



The central trappean belt, forming the mineral range proper, 

 varies in width from 2 to 3 miles, and extends throughout the 

 whole length of 140 miles, passing into the neighbouring State of 

 Wisconsin. The prevailing rock is mineralogically a dolerite, or 

 mixture of felspar (labradorite), hornblende, and augite, with chlorite, 

 epidote, calcite, and magnetite as occasional constituents. It is 

 usually of a dark-brownish -red or chocolate colour, mottled vrith 

 green or black by the chloritic material, but occasionally becomes 

 bright green, or even sulphur-yellow when epidote prevails, as is 

 the case in the Ontonagon district. 



More important, however, than the mineralogical constitution of 

 the traps is their physical structure, which varies considerably, the 

 commonest condition being compact, with finely granidar fracture, 

 * Geology of Canada, pp. 84-85, Atlas, p. 19. 



