PREVIOUS WORK. 21 



article was given an outline of the distribution of the various rocks for a 

 portion of the district, with their stratigraphical succession (p. 803), the dis- 

 cussion of the structure and correlation being left for the present report. 



The above-mentioned sketch map, with the maps by Burt, Foster and 

 Whitney, Brooks, Brooks and Wright, the section by Foster and Whitney, 

 and the section by Brooks, along the Paint and Michigamme rivers, are the 

 only maps or sections which, so far as can be learned, have been published 

 of that part of the Crystal Falls district under discussion. 



MISCELLANEOUS REFERENCES. 



JuLiBN, Alexis A. Ai)[)eiidix A. Lithology. Geol. of Michigan, Vol. II, 1873, 

 pp. 1-185. 



WiCHMANN, Arthur. Microscopical observations on the iron-bearing rocks 

 from the region sonth of Lake Superior. Brooks's Geol. of the Menominee Iron 

 Region, 1880, Chap. V, pp. 600-655. 



Wright, Charles E. Geology of Menominee Iron Region. Geol. of Wis- 

 consin, Vol. Ill, Part 8, 1880, pp. 665-741. 



Lane, A. O. In sketch of the geology of the iron, gold, and copper deposits of 

 Michigan. Rept. of State Board of Geol. Survey for 1891-92, 1893, p. 182. 



Patton, H. S. Microscopic study of some Michigan rocks. Rept. of State 

 Board Geol. Survey for 1891-92, 1893, p. 186. 



During the progress of the Michigan and Wisconsin State surveys 

 specimens froto outcrops were collected, and descriptions of these discon- 

 nected specimens are found in the State reports. 



References to the pages on which the individual descriptions may be 

 found will be given under the petrographical discussion of similar rocks 

 here described. 



UNPUBLISHED WORK. 



In 1891 a survey was organized by a private corporation, and put in 

 charge of Prof C R. Van Hise. He consented to take charge of this work 

 on the conditions that all maps and notes should be available for this report 

 and that no other compensation was to be made by the company. The 

 object of this survey, known as the Lake Superior survey, was to study that 

 jDart of Michigan of which Crystal Falls is the center, in order to determine 

 the feasibility and advisability of opening up the mines of that district. 

 This survey was vigorously prosecuted, and an excellent topocfraphic map 

 made of an area 32 miles north and south and 42 miles east and west, cover- 

 ing a large part of four 15-minute atlas sheets of the United States Geological 



