82 THE VERMILION IRON-BEARING DISTRICT. 



and the southern border of the argilHtes as they appear farther west. Tla- 

 entire system of gneisses, schists, and slates is regarded as belonging to one 

 structural system, as they all possess a common dip and pass by gradatioiis 

 into each other, both along the strike and across it (p. 181). The iron 

 bearing rocks are interlaminated with the country schists, and while they 

 exhibit much persistence in the direction of the strike, they do not continue 

 without interruption ; they appear in the midst of the schists sometimes as a 

 strictly local phenomenon (p. 182). In structure the region is a simple 

 synclinical fold, the strata of which have a thickness of 106,204 feet. The 

 succession, from the bottom upward, is granite, gneiss, micaceous and 

 hornblendic schists, graywacke, argillite-schist bearing conglomerates, and 

 sericitic and chloritic schists bearing iron ore (p. 191). As the plainly 

 fragmeutal rocks grade by imperceptible stages into the gneiss and the 

 gneiss into the granite, the whole is regarded as a sedimentary series (p. 193). 

 While granite pebbles are found in the conglomerates, these are not derived 

 from the iinderlying granite, as many of the fragments differ in character 

 from the inferior granite (p. 194). 



The author places the conglomerates stratigraphically below the iron 

 ores and jaspers. He makes the following statement: 



We find flints and jaspers, which, as far as we have explored, could not be 

 afforded by any part of this system. We find nothing which indisputably could 

 have been derived from anj' member of the system — the Vermilion S3^stem — ranging 

 from the granites to the earth}' schists. Those older rocks whose destruction afforded 

 material for the building of the Vermilion system belonged to an earlier age, and 

 were parts of an older system [pp. 194-195]. 



They all belong to one system, for no grounds were discerned which 

 would justify the division of this series of rocks into several systems 

 (p. 195). 



WiNCHELL, N. H. Geological report: Fifteenth Ann. Rept. Geol. and Nat. 

 Hist. Survey Minn., for 1886, 1887, pp. 209-399, with map. 



In this report Winchell gives very numerous details as to the geology 

 of northeastern Minnesota. A preliminary geologic map accompanies the 

 report. At several places there are transitions between the granite-gneiss 

 and a fine-grained mica-schist. In the syenite are sometimes found 

 angular fragments of mica-schist. The Vermilion group is defined as 

 including the lower portion of the complex series of schists designated as 



