106 KEMPS ORE DEPOSITS. 



placement. The beds thus formed may have been afterward 

 metamorphosed. Credner, Brooks, Wright in his published work, 

 and at first Irving, described them as having formed as beds of 

 limonite. These were conceived to have been metamorphosed in 

 the general metamorphism of the region. Brooks thought it pos- 

 sible that the hematites were altered magnetites, an idea confirmed 

 by the presence of martite, but he considered all to have been 

 limonite originally. Irving's views are set forth under Example 9c. 

 Yan Hise's latest work traces much the same relations as in the 

 less disturbed Gogebic district. He emphasizes the almost in- 

 variable occurrence of the ore along the contact of chert and in- 

 trusive dikes, which are now altered to so-called soapstone. This 

 relation is shown in Fig. 18. The ores are thought to have re- 

 placed these walls, synclinal troughs having been favorite points 

 of deposition. E. Reyer considered that the iron had been leached 

 from the neighboring, basic eruptive rocks (green schists), and had 

 'been precipitated as hydrate. The eruptives are, in this view, 

 regarded as submarine, and the similar association of basic erup- 

 tives with*the iron ores of Elba is commented on. 



2.02.22. It was in the forties that the importance and extent of 

 the ore bodies were first vaguely suspected. The trouble that they 

 made with the compasses of the early land surveyors indicated 

 their existence. Important mining began in 1854. Somewhat 

 over 100,000 tons were produced in 1860, over 800,000 in 1870, 

 nearly 1,500,000 in 1880. In 1877 the Menominee region was 

 opened, and in 1885 the Penokee-Gogebic and Vermilion districts 

 began to ship. The total shipments from the Lake Superior region 

 in 1890 were 8,982,531 tons. The total production to 1891 of the 

 Marquette district was 32,700,000 tons. A quite complete citation 

 of the literature is to be found in Wads worth's monograph, already 

 referred to, and in Irving's " Copper-bearing Rocks of Lake 

 Superior," Monograph No. V., II. 8. Geol. Survey. See also under 

 Examples 95, 9c, and 9d. Only the most important or most recent 

 papers are mentioned here. 1 



1 J. Birkinbine, "Resources of the Lake Superior District,'' M. E., 

 July, 1887. T. B. Brooks, Geol. Survey of Michigan, Vol. I., 1873; Geol. 

 Survey of Wisconsin, Vol. III., p. 450. H. Credner. " Die vorsilurischen 

 Gebilde df>r oberen Halbinsol von Michigan in Nord Amerika," Zeitsch. d. 

 d. Geol. Ges., 1889, XXL 516; also Berg.- und Huett. Zeit., 1871, p. 369. 

 Foster and Whitney, Geol. of the Lake Superior District, Vol. L, "Iron 

 Lands," 1851. R. D. Irving, "O i the Origin of the Ferruginous Schists and 



