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THE JOURNAL OF GEOLOGY.

Following Houghton, Messrs. Foster and Whitney[1] made an examination of the copper and iron regions of Michigan under the direction of the United States government. In their report on the copper lands, they described briefly the occurrences of dykes and flows of traps in the copper-bearing rocks of the south shore of the lake. Among them they distinguished compact, amygdaloidal, porphyritic, epidotic and brecciated varieties (pp. 69 and 70). In Part II. of the report, in their description of the iron region, they refer to the large dykes in the Animikie rocks on the north shore of the lake (pp. 12-13), and to the dykes of diabase cutting the Archæan schists in the neighborhood of Marquette, Michigan (pp. 18 and 39). They also gave a recapitulation of the characteristics of the traps of the entire region (pp. 85-94), with their chemical and mineralogical composition.

At about the same time that Messrs. Foster and Whitney were engaged in their survey of the copper and iron rocks, Dr. D. D. Owen,[2] with his assistants, was employed in making a geological reconnoissance of the states of Wisconsin, Iowa, and Minnesota. Messrs. D. D. Owen, J. G. Norwood, B. F. Shumard, Col. Whittlesey, and Major R. Owen examined a much larger area than did Messrs. Foster and Whitney, and were therefore not able to give as much detailed description of the rocks observed as the last named geologists succeeded in doing. They, however, mention the occurrence of sheet and dyke gabbros in Wisconsin, and of dyke gabbros in the Animikie of Minnesota.

Following these geologists came many others who examined the Lake Superior region in more or less detail, but added little to the knowledge of the trap rocks of the district, until, in 1871, Professor R. Pumpelly[3] published a paper on "The Paragenesis and Derivation of Copper and its Associates on Lake Superior," in which he described the melaphyres and other basic rocks associated with the copper on Keweenaw Point. After Pumpelly a number of geologists visited the region, but they devoted their

  1. ↑ Report on the Geology and Topography of a Portion of the Lake Superior Land District, Part I. Washington, 1850. Part II.,Washington, 1851.
  2. ↑ Report of a Geological Survey of Wisconsin, Iowa, and Minnesota.By D. D. Owen.Philadelphia, 1852, pp. 142-164, 285, 304-306, 342-417.
  3. ↑ Am. Jour. Sci. (3) II., 1871, p. 188.
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