226 W. E. Logan on the Rocks of Canada. 
In respect to the age of the Huron cupriferous formation, the 
evidence afforded by the facts collected by my friend and associ- 
ate, Mr. Murray (published in our Report of Progress for 1847— 
48), on the Grand Manitoulin, La Cloche, Snake, Thessalon, Sul- 
phur, and other islands, points ranging along a line of 90 miles 
out in front of the coast, is clear, satisfactory, and indisputably 
conclusive. On these islands, the Potsdam sandstone, the Tren- 
ton limestone, the Utica slates, and the Loraine shales, successive 
formations in the lowest fossiliferous group of North America, 
were each, in one place or another, found in exposures denuded 
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 accompanying strata, filling up valleys, 
overtopping mountains, and concealing every vestige of dykes and 
copper veins ; and it would appear that some of these mountains 
have required the accumulation of the whole thickness of the low- 
est three and part of the fourth fossiliferous deposit, equal to about 
700 feet, to bury their summits. 
there are considerable areas without amygdaloid, while white. 
sandstones are present in others, as on the south side of Thunder 
Bay, though not in the same vast amount, or the same state 0 
Vitrification as those of Huron. But notwithstanding these differ- 
ences, there are such strong points of resemblance in the inter- 
stratification of igneous rocks, and the general mineralized condi- 
tion of the whole, as to render their proximate equivalence highly 
probable ; and the conclusive evidence given of the age of the 
Huron would thus appear to settle that of the Lake Superior 
rocks in the position given to them by Dr. Houghton, the late 
State Geologist of Michigan, as beneath the lowest known Amerr 
can fossiliferous deposits; and in this sequence those of Lake : 
Huron, if not those of Superior, would appear to be contemporane- 
ous with the Cambrian series of the British Isles. : 
The eastern limit of this formation on Lake Huron is in the 
vicinity of Colling’s Inlet, opposite the eastern extremity of the 
great Manitoulin Island, whence it gradually recedes inland, t@ 
ing a northeastern course; and farther down the St. Lawrence 
and its lakes, the Lower Silurian appear to rest upon gueissoid 
rocks without the intervention of the Cambrian. 
Ifa line be drawn on the map in continuation of the iia 
River and Lake Champlain valleys to the vicinity of sean 
about thirty miles above Quebec, and thence in a northeastwar” 
direction, it will divide the country into two areas, which, though 
nearly resembling one another in the general formations of w i 
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