16 THE CRYSTAL FALLS IRON-BE AEING DISTRICT. 



Foster, J. W., and Whitney, J. D. Report on the geology of the Lake Supe- 

 rior hiud district. Part II. The iron region, together with the general geology. 

 Thirty-second Congress, special session, 1851; Senate documents, Vol. Ill, No. 4, 

 pp. 406, with maps and section. 



In 1851 there was published a report by Foster and Whitney on the 

 iron regions of the Lake Superior land district, tog-ether with the general 

 geology. This gives the first connected account of the results obtained by 

 the various surveyors who had been engaged on the Government surve)^ of 

 the Upper Peninsula of Michigan. Accompanying this report there are 

 two colored maps and a section. The subdivisions of the rocks as made by 

 Burt in the Crystal Falls district are not retained in this report by Foster 

 and Whitney. The map is generalized, and the hornblende-slates, etc., of . 

 Bui-t are included under the general term " crystalline schists," and are 

 placed by the authors in the Azoic system. There are represented here and 

 there tlu'oughout this Azoic area a trappean knob and bed of marble. 



The granite area shown on Burt's map is very much reduced in size, 

 and no longer connected with the large granite areas to the east. The 

 granite on the lower reaches of the Michiganune, in T. 42 N., R. 31 W., is 

 here indicated for the first time. In these respects only does this portion 

 of the map show a decided advance in knowledge of the distribution of the 

 rocks. A copy of the map, showing the distribution of the rocks by 

 symbols instead of colors, is reproduced as fig. 2. 



Brooks, T. B. The iron-bearing rocks (economic). Geol. Survey of Michigan, 

 Vol. I, Part I, 1873, pp. 319. With Atlas Plate IV and general map, by Romiuger, 

 Brooks, and Pumpelly. 



The next mention of the district that I have been able to find was 

 made in 1873 by Maj. T. B. Brooks, in his report on the iron-bearing rocks 

 of Michigan. 



However, this report seems to show a decided decrease in knowledge 

 from that possessed by Burt concerning the geology of this district. It is 

 time that indications of iron had been seen, but the observations made were 

 so meager that nothing could be done toward determining the relations of 

 the rocks or um-aveling the structure of the area. 



Upon the map accompanying the report (Greol. Survey of Michigan, 



