590 THE JOURNAL OF GEOLOGY. 



rocks of the Eagle River section of Keweenaw Point into green- 

 stone or fine-grained diorites, feldspathic traps or coarse grained 

 diorites, and traps, including the melaphyres and amygdaloids. 



Before the publication of the reports of the Wisconsin survey, 

 Messrs. Streng and Kloos 1 communicated the results of their 

 examination of certain Keweenawan rocks occurring in Minnesota 

 and in Wisconsin about the head of Lake Superior. Streng, who 

 did the microscopical work of the investigation, recognized among 

 his specimens melaphyres, augite-diorites, quartz-diorites and a 

 hornblende-gabbro to which reference has already been made in 

 a former article. 2 Pumpelly 3 also had devoted his attention to 

 the rocks of the copper series. He studied more pafticularlv the 

 fine and coarse-grained diabases and melaphyres of Keweenaw 

 Point. 



With the publication of Volume III. of the Geological Survey 

 of Wisconsin a more general classification of the Keweenawan 

 rocks of Northern Wisconsin and of Keweenaw Point in Michigan- 

 was given by the same author. 4 He distinguished among them 

 diabases, hornblende and orthoclase-gabbros, melaphyres, augite- 

 diorites and porphyrites, the characteristics of which will be 

 mentioned when the discussion of the diabases and gabbros of 

 Keweenawan age is taken up. In the same volume Irving described 

 the rocks of the Huronian of Wisconsin, among which he found 

 gabbros (p. 147), and those of the Keweenawan in the same state 

 (pp. 168 to 193). The hornblende-gabbros and the augite-diorites 

 of Pumpelly he regarded as altered gabbros and diabases, and not 

 as original hornblende rocks. Julien 5 also gave a very excellent 

 account of the microscopic appearance of two olivine-diabases 



1 A. Streng and J. H. Kloos: Ueber die Krystallinischen Gesteine von Minne- 

 sota in Nord Amerika. Neues Jahrb. f. Min., etc., 1877, pp, 31, 1 13, 225. 



2 This Journal, Vol. I., p. 447. 



3 R. Pumpelly : Metasomatic Development of the Copper-Bearing Rocks of 

 Lake Superior. Proc. Am. Acad, of Arts and Sciences, 1878, XIII., Part II., pp. 253- 

 309- 



4 Geology of Wisconsin, III., 1880, p. 29. 



s A. A. Julien : Microscopic Examination of Eleven Rocks from Ashland county 

 Wisconsin. Geol. of Wisconsin, III., 1880, p. 224. 



