96 Minnesota . Icademy of Science 



tree near the present site of Biwabik. Test-pitting- there by 

 W. J. Merritt soon disclosed the Biwabik ore body. 



I p to the time of these discoveries all accounts of the Mesabi 

 region refer principally to the east end of the range, where the 

 ore formation is changed to hard magnetite rocks by the Duluth 

 gabbro and the Kmbarrass granite. There, on account of its 

 indurated character, the ore formation does not concentrate to 

 iron ore by weathering as does the greenalite in the central and 

 western part of the range. As soon as the rich ore at Biwabik 

 and Iron Mountain was discovered prospectors rushed to the 

 district and for several years explorations were carried on vigor- 

 ously. The Geological and Natural History Survey represented 

 by Profs. N. H. and H. V. Winchell, aided by new data gained 

 from test pits, attacked the problem vigorously at the very be- 

 ginning of the new development. In 1892 a report was pub- 

 lished showing the distribution of rocks and ore formation, in- 

 cluding the discovery of Merritt. 



In 1894 the Survey published a report and detailed maps 

 of the Mesabi Range. This report was by J. F. Spurr of that 

 survey, and brought knowledge of the new range down to date. 

 The maps of the report which include the greater portion of 

 the district, show the Virginia-Eveleth loop, the relations to 

 granite and gabbro at the east part of the range, and the essen- 

 tial geological features and boundaries of the ore formation. 

 As new data were accumulated these delineations of the boun- 

 daries of the ore formation proved to be remarkably accurate. 

 Maps of the entire region were published later in Vol. 4 of 

 the Final Report, 1898. The reports early and late contain 

 comprehensive discussions of the origin of the ore and analyze 

 extensively current opinions of iron ore genesis. 



Regarding the genesis of the Minnesota iron formations, 

 Prof. Winchell maintained that the iron was precipitated in ancient 

 seas, but that there were contributions to these seas from igneous 

 material probably while the latter was in a heated condition. This 

 theory includes some novel features, and, so far as I am aware, 

 was presented by Prof. Winchell for the first time. 



Concerning Prof. Winchell's interpretation of the geologic 

 structure of the iron region, we find in his earliest reports that 

 they are of pre-Cambrian age and the recognition of deposits of 



