THE COPPER-BEARING ROCKS OF LAKE 
SUPERIOR. 
BY R. D. IRVING. 
CoH. Az PT Halts I. 
INTRODUCTORY. 
Aim of this memoir.—Obstacles to the earlier accomplishment of this aim.—Investigations necessary to 
it.—Time allotted to these investigations.—Plan of field work.—Special areas studied by the sev- 
eral parties.—Acknowledgments of outside assistance.—Explanation of the irregularities in the 
amount of detail used in this memoir.—Previous examinations and accounts of the copper-bearing 
rocks of Lake Superior.—List of works from which facts have been drawn for this memoir.— 
General nature of the information drawn from each.—Account of different theoretical views as 
to the origin and geological relations of the copper-bearing rocks.—Different views as to the origin 
of the conglomerates; of the “traps” and amygdaloids; of the felsitic rocks.—Different views 
as to the geological relations of the copper-bearing rocks.— Use of the term ‘‘Keweenawan.”—These 
conflicting views have arisen in large measure from the small scope of the examinations of any 
one geologist.—Literature of the subject. 
This memoir aims at a general exposition of the nature, structure, 
and extent of the series of rocks in which occurs the well-known native 
copper of Lake Superior. 
This is a work which has never been attempted before, nor could it 
have been accomplished sooner. A number of geologists have written on 
different portions of the Lake Superior basin during the past fifty years, 
but until very recently any attempt to compile a general account of the 
copper-bearing rocks would have met with some insuperable obstacles. Not 
to speak of the difficulties to be encountered in trying to reconcile the con- 
flicting statements of different authors, any one making the attempt would 
have met the two serious obstacles of nearly complete ignorance as to the 
nature of the crystalline rocks which form so large a part of the series, and 
complete ignorance as to the distribution and structural relations of the 
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