588 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), an d to the dykes of 

 diabase cutting the Archaean schists in the neighborhood of Mar- 

 quette, Michigan (pp. 18 and 39). They also gave a recapitula- 

 tion 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. Whit- 

 tlesey, 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 asso- 

 ciated 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, 1 850. 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. 



3Am. Jour. Sci. (3) II., 1871, p. 188. 



