12 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
recognized such rocks among the pebbles of the conglomerates, but as 
massive rocks they have only been noticed by Foster and Whitney, Logan, 
N. H. Winchell, Macfarlane, and Bell. Foster and Whitney, who noticed 
them on Mount Houghton and in the Porcupine Mountains, looked on them 
as baked sandstones, the baking being regarded as due to the heat of the 
molten traps. Winchell has noticed them on the Minnesota coast, but re- 
gards them again as altered sedimentary rocks.” Logan* and Macfarlane* 
have observed them only on Michipicoten Island, where Macfarlane seems 
to regard them as eruptive and Logan as fused sedimentary material. Bell 
merely mentions the existence of quartziferous porphyry on Lake Nipigon.? 
The failure to recognize the importance and eruptive origin of these rocks 
is peculiarly strange in the face of the almost universal association in vol- 
canic regions of the two types of acid and basic eruptives. 
Widely divergent views have been held with regard to the geological 
relations of the series as a whole, as well as with regard to the origin and 
structural relations of its constituent rocks. In the earlier days of the study 
of Lake Superior geology the general lithological similarity between these 
rocks and the Triassic sandstones and eruptives of the eastern states led 
to the view that they were of the same age. This view was held by 
Houghton,® and at one time by Jackson,’ and latterly has been advo- 
cated by Bell.* Later, when the Cambrian age of the so-called ‘“EKastern 
Sandstone”, which forms the south shore of Lake Superior from the Sault 
westward to the east side of Keweenaw Point, came to be established, the 
copper-bearing rocks, being regarded as belonging to the same formation, 
were considered to be the equivalents of the Potsdam sandstone of New 
York. This is the position taken by Foster and Whitney,’ Owen,” Ro- 
1Op. cit., pp. 64-65. 
2Bighth Annual Report of the Geological Survey of Minnesota, pp. 23-26. Ninth Annual Report, 
pp. 12, 17, 31, 32, ete. 
3Geology of Canada, 1863, pp. 81-82. 
4Geological Survey of Canada, Report of Progress, 1863-66, p. 142. 
5Report of Progress of the Geological Survey of Canada, 186669, p. 348. 
6Am. J. Sci., 1843 (1), XLV, 160. 
7Am. J. Sci. (1), XLIX, pp. 81-93. 
®Report of Progress Geological Survey of Canada, 1866—69, p. 321. 
9 Op. cit., p. 99. 
10Geological Survey of Wisconsin, Iowa, and Minnesota, pp. 187-196. 
