336 THE AZOIC SYSTEM AXD ITS SUBDIVISIONS. 



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

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

 Ste. Marie ; on the east the same supporting granite was observed by Mr. 

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

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

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

 .... In respect to the geological age of the formation, the evidence afforded 

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

 and indisputably conclusive, .... successive formations of the lowest fossil- 

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

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

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

 quartz rock, and its accomj)anying strata, fiUmg up valleys, overtopping moun- 

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



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

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

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

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

 important masses of interstratified greenstone exist without amygdaloid, while 

 white sandstones are present in others, as on the south side of Thunder Bay, 

 though not in the same state of vitrification as those of Huron. But notwith- 

 standing these differences, there are such strong points of resemblance in the 

 iuterstratification of igneous rocks, and the general mineralized condition of 

 the whole, as to render their positive or proximate equivalence highly probable, 

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

 Huron, would thus appear to settle that of the Lake Sui^erior rocks, in the 

 position given to them by Dr. Houghton, the late State Geologist of Michigan, 

 as beneath the lowest known fossiliferous deposits, a position which, as will be 

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

 your Excellency in 1846, appeared to me to derive some support from evidences 

 on the Canadian side of Lake Superior itself." (I. c, pp. 8, 9, 19, 20.) 



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

 lithological evidence, applied to rocks at great distances from one an- 

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

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

 and in that for 1846-47 (p. 34) regarding Dr. Houghton's views are 

 erroneous. (Bull. Mus. Comp. ZooL 1880, VIL (Geol. Series I.) 83.) 

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

 rocks of Lake Superior at the 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 ) VII. 207-209. Report 

 Brit. Assoc. Adv. Sci., 1851, Trans. Sec, pp. 59-62. Am. Jour. Sci., 

 1852, (2 ) XIV. 224-229.) In these publications the copper-bearing 



