4 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
the Poreupine Mountains, while Messrs. Campbell and McKinlay took the 
western part. 
Besides the aid received from those directly connected with the work, 
I have to thank for assistance also a number of others, and especially the 
following gentlemen: Professor 'T. C. Chamberlin, for notes of observations 
on Snake River, Minnesota; Professor A. H. Chester, of Hamilton College, 
Clinton, N. Y., for a series of notes, accompanied by specimens, on the rocks 
of the Vermillion Lake region, and of the north shore of Nipigon Bay; 
A. R. C. Selwyn, Director of the Geological Survey of Canada, for informa- 
tion and for a suite of specimens illustrating Macfarlane’s reports on Michipi- 
coten Island; Professor N. H. Winchell, State Geologist of Minnesota, for 
loan of township plats of the Minnesota coast, and for information with 
regard to the back country between Pigeon River and the lake shore; Frank 
Klapetko, of the Delaware Mine, Keweenaw Point, for measurements made 
in the vicinity of Lac La Belle; Messrs. John Chassells and J. R. Devereux, 
of Houghton, for sundry favors; B.C. Chynoweth, agent of the Mass mine, 
Ontonagon, for assistance in that region; and B. N. White, of Ontonagon, 
for information as to the course of the slate belt of the Porcupine Moun- 
tains to the eastward. Mr. White had traced out this belt to some distance 
east of the Ontonagon, and kindly gave to me all the results of his labor. 
The combination of the results of previous work and of new original 
observations, by which this memoir must be made up, have compelled great 
irregularity in the amount of detail given in describing the different dis- 
tricts. So far as the statements are based upon older work, detail has been 
generally omitted, but whenever I have felt it necessary to differ from pre- 
vious writers, and in all new descriptions, I have used detail freely. 
The list of geologists who have during the last fifty years, from time to 
time, written on the group of rocks which forms the subject of this memoir 
isa long one. Omitting the names of those whose writings have not been 
based on personal examinations, or have been preceded only by very 
slight examination, or are obviously unworthy of notice from lack of geo- 
logical knowledge on the part of the authors, I may mention the fol- 
