32 THE VERMILION IRON-BEARING DISTRICT. 



of the future are likely to occur, have been prepared. On these plates 

 the exposures actually seen during the field work have been indicated, 

 drawn to very nearlj^ correct scale. Many of the exposures are so small 

 that in order to represent them on the maps at all it has been necessary to 

 exaggerate them. On these maps are given the data which were used as 

 the basis for drawing the formation lines in these economically important 

 areas. If anyone is unable to accept the conclusions reached, he may 

 draw his own inferences from the data given, which are essentially correct, 

 although, as will be understood by those who know the limitations under 

 which such geologic mapping is done, a number of minor errors may be 

 disclosed by very close work and very exact location of exposures with 

 instruments of precision. All geologic maps are but approximations to the 

 truth. The aim has been to inake the present approximation as close as 

 practicable. 



A great deal of time has been devoted to examining all available literature 

 that refers in any way to this district. Fairl}?- complete quotations are made 

 from the various works cited, so that a cargful reading of the review of the 

 literature will enable one to familiarize himself with the changes of opinions 

 concerning the structure, character of rocks, and other details, and also with 

 the gradual increase in knowledge concerning the geology of the district. 



GEOGRAPHIC lilMITS. 



The territor}^ designated by the name "Vermilion iron-bearing district" 

 lies in the extreme northeastern portion of Minnesota, including portions 

 of St. Louis, Lake, and Cook counties. The district has an area of 

 approximately 1,000 sqtiare miles. It is a narrow belt extending east- 

 northeast from near the west end of Vermilion Lake, in longitude 92° 30' 

 west from Greenwich, on the west, to the vicinity of Gunflint Lake, on the 

 international boundary, on the east, in about longitude 90° 45' west from 

 Greenwich. The district lies between 47° 15' and 48° 15' north latitude. 

 It attains its maximum width at the west, where it is about 18 miles wide, 

 and gradually narrows eastward, until at Gunflint Lake its minimum width 

 is 2 miles. The geographic relations of the Vermilion iron-bearing district 

 of Minnesota to the other iron-bearing districts of the Lake Superior region 

 can be seen on PL I. 



The western limit of the district as given on the map (92° 30') is purely 

 arbitrary. West of this the country is heavily drift covered and timbered, and 



