6 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
of the Keweenawan System,” published in Vol. III of the Geology of Wis- 
consin, 1880; my own reports on the ‘Geological Structure of Northern 
Wisconsin” and ‘‘Geology of the Eastern Lake Superior District” of Wis- 
consin, both in Vol. III, Geology of Wisconsin, 1880; E. T. Sweet’s 
report on the ‘Geology of the Western Lake Superior District,” in the 
same volume; T’. C. Chamberlin’s and M. Strong’s joint report on the 
‘Geology of the Upper St. Croix District,” also in the same volume; and N. 
H. Winchell’s “Ninth Annual Report of the Geological and Natural History 
Survey of Minnesota,” 1880. 
In every case where I have taken information from these works I have 
indicated it by direct reference. It will, perhaps, be well to give a gen- 
eral statement here as to the extent of my indebtedness to each of them. 
Foster and Whitney’s work applies solely to that portion of the copper- 
bearing series which is included within the state of Michigan, 7. e., to the 
region lying between the eastern extremity of Keweenaw Point and the 
Montreal River, and to Isle Royale. For my statements as to Isle Royale I 
have had to depend almost exclusively upon this work, read in the light 
of my own experience. The former district I have myself examined, and 
have only used Foster and Whitney’s statements, chiefly to aid in mapping, 
as supplementary to my own observations. Logan, in his geology of 
Canada, describes briefly all of the rocks of the north and east shores of 
Lake Superior from the Minnesota boundary to the Sault. I have only 
drawn from him, however, for the east coast, Michipicoten, and the islands 
south of Nipigon Bay. Macfarlane’s “‘ Report on Lake Superior” includes 
a further description of Michipicoten Island and the east coast, having been 
based on more detailed observation than that of Logan. I have drawn 
somewhat from this report, but especially have used it for locating the series 
of Michipicoten rocks sent me by Mr. A. R. C. Selwyn, and which I de- 
scribe microscopically in Chapters III and VII. The same writer’s account 
of the Geology of Wood’s Location has aided me in reading rapidly the 
structure of the peninsula between Black and Thunder bays, though I 
differ from him in some of his most important conclusions. Dr. Bell’s sev- 
eral reports on the geology of that portion of Canada north and east of 
Lake Superior, including a manuscript map based on them, have been 
