118 THE VERMILION IRON-BEARING DISTRICT. 



Vol. IV. This general discussion of Vol. V is reviewed, with such 

 reference to the facts recorded in Vol. IV as is necessary to make the 

 summary intelligible. 



Dr. Grant's views, as indicated in the detailed descriptions of special 

 areas, in some cases differ somewhat widely from those of Professor 

 Winchell. 



Winchell discusses the general structural geology of northeastern 

 Minnesota. The ancient rocks of this area he places in two main S3"stems, 

 the Archean and the Taconic. The former is further subdivided into the 

 Upper and Lower K eewatin, separated from each other by an unconformity. 

 The Pewabic quartzite also is placed with the Keewatin, but is not 

 assigned to either of the main divisions. Overlying the Archean with 

 strong unconformity is the Taconic, represented by Animikie and Kewee- 

 nawan rocks, these divisions being supposed to represent, respectively, 

 the Lower and Middle Cambrian of other parts of the country. The 

 Coutchiching and Laurentian rocks before mapped as separate formations 

 are now included within the Keewatin. 



The Lower Keewatin comprises greenstone, with associated surface 

 volcanics which are both subaerial and subaqueous, argillitic slates, siliceous 

 schists, quartzites, arkoses, " greenwackes," iron ores, and marble. 



The greenstone, designated the Kawishiwin, is the oldest known rock 

 in the State, and is supposed to represent a portion of the original crust of 

 the earth. With its associated volcanic rocks it occurs in two main belts. 

 The southern belt begins in the Adcinity of Gunflint Lake and extends 

 indefinitely westward b}^ way of Gobbemichiganmia Lake, the Kawishiwi 

 River, White Iron Lake, and Tower. The northern belt of greenstone 

 enters the State from Hunters Island, appearing conspicuously at the south 

 side of Basswood Lake. At Pipestone Rapids and Fall Lake it widens 

 southward and apparently unites at the surface with the southern belt, the 

 overlying Upper Keewatin being absent for a distance of a few miles. But 

 farther west it is again divided by the Stuntz conglomerate, the northern 

 arm running to the north of Vermilion Lake, west of which its extension 

 is unknown, and the southern one running south of the lake. 



The fragmental stratified rocks of the Lower Keewatin are most impor- 

 tant toward the western part of the area of exposure of crystalline rocks. 

 They occupy a wide area south, west, and north of Tower. The iron ores 



