Page:The Journal of geology (IA journalofgeology11893univers).pdf/169

This page has been proofread, but needs to be validated.
THE BASIC MASSIVE ROCKS, ETC.
595

ties of the gabbro of the region, but no detailed descriptions of these rocks, nor of the ordinary gabbros, whose modified forms they are supposed to be, are given. Finally, Dr. A. C. Lawson[1] has mentioned some of the characteristics of certain diabases from dykes in the Archæan rocks of the Rainy Lake region, in which the gabbroitic as well as the diabasic structures are well exhibited, the former toward the centers and the latter near the sides of the masses.

The most comprehensive treatment of the "greenstones" and "greenstone schists" of the Lake Superior region is that by Dr. G. H. Williams[2] in his bulletin on the origin of the green schist, supposed to underlie the Huronian in Michigan. In this volume the author not only describes the petrographical features of the schists with which he deals, but he likewise describes in some detail the microscopical characteristics of the diabases, diabase porphyrites, diorites, dioritic porphyrites and gabbros, associated with the schists, and from some of which the latter have been derived.

Within the past three years a number of papers have appeared in which reference is made to some of the special features of a few of the coarse basic rocks, both north and south of the lake, but no articles have been published that deal with their general features. Fairbanks[3] has communicated a few notes on the diorites and gabbros in the province east of the north side of Lake Superior. Irving and Van Hise[4] have given a brief synopsis of the characteristics of the diabase dykes and interbedded sheets in the Penokee iron series on the south side

  1. ↑ A. C. Lawson: Notes on Some Diabase Dykes of the Rainy Lake Region. Proc. Can. Inst. for 1887, and Report on the Geology of the Rainy Lake Region.Pt. F., Ann. Rep. Geol. and Nat. Hist. Survey of Can. for 1887-88, pp. 57-73 and 147-164.
  2. ↑ G. H. Williams: The Greenstone Schist Areas of the Menominee and Marquette Region of Michigan.Bull. No. 62.U. S. Geol. Survey, 1890.
  3. ↑ H. W. Fairbanks: Notes on the Character of the Eruptive Rocks of the Lake Huron Region.Amer Geologist, I.1890, p. 162.
  4. ↑ R. D. Irving and C. R. Van Hise: The Penokee Iron-bearing Series of Northern Wisconsin and Michigan.Monograph XIX., U. S. Geol. Survey, 1893.Chap. VII., The Eruptives.
This article is issued from Wikisource. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.