CHAPTER x; 
THE COPPER DEPOSITS. 
No special investigation made of the copper deposits.—Different kinds of copper deposits.—Cupriferous 
sandstones and conglomerates.—Cupriferous amygdaloids.—Epidote belts.—Transverse veins.— 
Similarity in origin of the several forms of copper deposit.—Source of the copper, and cause of 
its precipitation; different views.—Rules to guide the explorer for copper.—Portions of the 
Keweenaw Series favorable and unfayorable to the occurrence of copper.—Prospects of future 
developments of copper without the present producing districts: in the Bad River country of 
Wisconsin; between Bad River and the Saint Croix; in the Saint Croix Valley; on the Douglas 
County Copper Range; on the Minnesota side of Lake Superior; on Isle Royale. 
A special study of the copper deposits of the Keweenaw Series 
formed no part of the plan of the investigation upon which this memoir is 
based. These deposits, were, of course, already the best known things 
about the series, and any study made with the hope of adding materially 
to the facts collected by the numerous geologists who have hitherto written 
upon them would have occupied far more than the whole time at com- 
‘mand. For the sake of rounding off the subject, however, I may appropri- 
ately offer a general account of the structural and genetic relations of these 
deposits, adding a few general considerations of an economic bearing as a 
guide to the future explorer for copper, both within and without the present 
producing districts. 
All the workable deposits of copper heretofore discovered in the Lake 
Superior region fall into one or other of two classes, which we may term 
belt or bed deposits, and transverse vein deposits. The first class includes 
the cupriferous conglomerates and sandstones, the cupriferous amygdaloids, 
and most, if not all, of the so-called veins carrying much epidote and coin- 
ciding with the bearing of the formation ; the second class includes those 
veins which traverse the formation in a direction more or less nearly at 
right angles to the bedding. No copper has ever been observed in connec- 
tion with the acid eruptives of the series, nor have any workable deposits 
been discovered in the massive non-vesicular diabase beds, except as dis- 
tinctly subordinate to, and directly connected with, the amygdaloid deposits 
or epidote courses, and always accompanied with an extreme degree of 
alteration. 419 
