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335 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



tion ; on tlie west it seems to repose on the granite, whicli was represented in 

 my report on Lake Superior as running to the east of Gros Cap, north of Sault 

 Stc. Marie ; on the east the same supporting granite was obst^rved by Mr. 

 Murray north of La Cloche, between three and four miles in a straight line up 

 the Eivicre an Sable, .... and again, about an equal distance up another 

 and parallel tributary, .... in both cases about ten miles from tlie coast. 

 . . . . In respect to the geological age of the formation, tlie evidence alforded 

 by the facts collected last year by Mr. Murray .... is clear, satisfactory, 

 and indisi)utably conclusive, .... successive formations of the lowest foRSil- 

 iferous group of North America, were each in one place or the other found, m 

 exposures divested of all vegetation, resting in unconformable repose, in a 

 nearly horizontal position, upon the tilted beds, and undulating surface of the 

 (luart/ rock, and its accompanying sti'ata, filling up valleys, overtopping momi- 



tains, and concealing every vestige of dykes and copper veins The 



chief diilerence in the copper-bearing rocks of Lakes Huron and Superior, 

 seem to lie in the great amount of aniygdaloidal trap present among the lat- 

 ter, and of white (luartz rock or sandstone among the former. But on the 

 Canadian side of Lake Superior there are some considerable areas, in which 

 important masses of interstratilied greenstone exist without amygdaloid, while 

 white sandstones are present in otliers, as on the south side of Thunder 15ay, 

 thou<di not in the same state of vitrification as those of Huron. But notwith- 

 standing these ditferences, there are such strong points of resemblance m the 

 interstrraihcation of igneous rocks, and the general minerahzed c<,iKhtiou of 

 the whole, as to render their positive or proximate e(iuivalence highly probable, 

 if not almost certain ; and the conclusive evidence given of the age oi the 

 Huron wouKl thus appear to settle that of the Lake Superior rocks, m the 

 position given to them l)y Dr. Houghton, the late State Geologist oi Michigan, 

 as beneath the lowest known fossilifer.Ris deposits, a position wliich, as will be 

 seen by a reference to the Keport of Progress I had the honor to submit to 

 your Excellency in 184G, appeared tome to derive some support from evideuces 

 on the Canadian side of Lake Superior itself." (l. c, pp. 8, 9, 10, 20.) 



In this is to be seen one of the attempts to decide geological ago by 

 lithological evidence, applied to rocks at great distances from one un^ 

 other, — a failure, in this case at least, as will bo seen farther on. One of 

 the writers has pointed out olscwberc that the statements in this report 

 and in that for 184G-47 (p. 34) regarding Dr. Houghton's views are 

 erroneous. (Ihill Mus. Gomp. Zool. 1880, VIL ((Jeol. Series L) 83.) 

 The views which Logan held regarding the age of the copper-bearing 

 rocks of Lake Superior at Hie time of the publication of the report from 

 which quotations have just been made, were published later in several 

 papers. (Bull Soc. Geol. France, 1849-50, (2 ) VIL 207-209. Report 

 Brit. Assoc. Adv. Soi., 1851, Trans. Sec., pp. 59-G2. Am. Jour. 8c.., 

 1852, (2 ) XLV. 224-220.) Li these publications the copper-bcanng 



