THE BASIC MASSIVE ROCKS, ETC. 589 



time principally to the discovery of the relations existing between 

 the several rocks, and made no efforts to divide these into their 

 varieties. 



With the establishment of the surveys of Minnesota, 

 Michigan, and Wisconsin, however, an attempt was made to 

 classify with scientific accuracy the basic rocks of these three 

 states. Kloos 1 had already discovered the gabbro of Duluth 

 and had identified a melaphyre from the same place, but had 

 made no very exact determination of either. Among the geol- 

 ogists on the Michigan and Wisconsin surveys, Messrs. Julien, 

 Wright, Wichman, Pumpelly and Irving examined microscopi- 

 cally the rocks of the Huronian and the Keweenawan series of 

 Wisconsin, and of the Archsean, Huronian and Keweenawan of 

 Michigan, and among the descriptions of these rocks which they 

 give may be found very exact accounts of the characteristics of 

 the diabases, gabbros and other basic eruptives of the region. 



Messrs. A. A. Julien 2 and C. E. Wright, 3 as early as 1873, 

 mentioned quite fully the greenstones and traps of the Archaean 

 and of the iron-bearing formations in Michigan. The former 

 writer identified many massive and schistose rocks to which he 

 gave the name of diorite, since he found in them hornblende, but 

 no augite. Mr. Wright likewise discovered hornblende rocks 

 which he evidently regarded as original, since he calls them all 

 diorites. Mr. Wright's determinations are the first ones based 

 upon microscopical observations of Lake Superior rocks. Messrs. 

 Brooks 4 and Pumpelly 5 contented themselves with macroscopic 

 examinations of the basic rocks of the iron and copper-bearing 

 series in this state, and in this way distinguished diorites, 

 melaphyres and amygdaloids, while Mr. Marvine 6 divided the 



r J. H. Kloos: Geologische Notizen aus Minnesota. Zeits. d. deutsch. geol. 

 Gesell. XXIII., 187 1, p. 417. Trans, by N. H. Winchell, 10th Ann. Rep. Geol. and 

 Nat. Hist. Survey of Minnesota, for 1881, p. 193. 



2 A. A. Julien : Geological Survey of Michigan, Vol. II., 1873, Appendix A, p. 41. 



3C. E. Wright: lb. Appendix C, p. 213-231. 



4 T. B. Brooks: Geological Survey of Michigan, Vol. I., 1873; P art !■» Iron-Bear- 

 ing Rocks, pp. 99-104. 



5R. Pumpelly : Part II., Copper District, lb. pp. 7-16. 



6 A. R. Marvine : Part II., Copper District, lb. pp. 95-1 16. 



