BULLETIN OF The geological society of AMERICA 

 Vol. 23, pp. 317-328 July 15, 1912 



PEOGEESS OF OPIXIOX AS TO THE ORIGIX OF THE LAKE 



SUPERIOR IROX ORES^ 



BY N. n. WINCHELL 



{Head hi/ title before the Society December 27, 1911) 



CONTENTS 



Page 



The report of Foster aud Whitney 317 



Charles Whittlesey's theorj' of segregation 320 



The work of R. D. Irving 322 



J. E. Spurr's investigation of the Mesabi ores 323 



Sedimentation 323 



Divergence of views between the surveys 324 



N. H. Winehell's studies of basic igneous rocks 324 



The Report of Foster and Whitney 



Tlie celebrated report of Foster and Whitney on the geology of the 

 Lake Superior land district, part II, 1851, was written, so far as con- 

 cerns the iron ore of the region, by Prof. J. D. Whitney. It embraces 

 the earliest discussion of this question, so far as the writer has observed, 

 and can be summarized briefly as follows : 



Quoting examples of the occurrence of crystals of specular and mag- 

 netic oxides of iron on the walls of volcanic craters, and in clefts and 

 cavities where they could be attributed to sublimation from great heat, 

 he is led to regard sublimation as one of the two factors in the production 

 of iron ores of the Marquette district. Internal, as well as volcanic, heat 

 was with Whitney a fundamental and active postulate in much of his 

 geological reasoning. The other factor he supposed to have been simply 

 igneous eruption, these oxides having been '^poured out" from the interior 

 of the earth in a plastic state. The former factor seemed to be required 

 to account for the minuteness of the distribution of oxides, and to explain 

 their banded structure in those cases where the oxide is closely incorpo- 

 rated in "metamorphic products," such as "jasper, hornstone, chert, chlo- 

 rite, and talcose slate." It was the assumed "metamorphic" origin of 

 these that made easy the assumption that the contained bands of iron 

 ore were due to heat and therefore to sublimation. The actual molten 



^ Manuscript received l»y the Secretary of the Society .Tanuary 9, 1912. 



XXIII— RiLi.. CKf.i,. See. Am., Vol. 23, 1911 (317) 



