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THE JOURNAL OF GEOLOGY.

rocks of the Eagle River section of Keweenaw Point into greenstone 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 particularly 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 Minnesota in Nord Amerika.Neues Jahrb. f. Min., etc., 1877, pp, 31, 113, 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.
  5. ↑ A. A. Julien: Microscopic Examination of Eleven Rocks from Ashland county Wisconsin.Geol. of Wisconsin, III., 1880, p. 224.
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