14 THE GEOLOGY OP MINNESOTA. 



[The Lower Keewatin . 



transition seems rather to have been of the nature of a change from massives to 

 surface lavas and volcanic ash, accompanied in some places by extensive oceanic 

 distribution and sedimentation. These rocks extend east and west in two conspicuous 

 belts. The southern belt begins in the vicinity of Gunflint lake and extends west- 

 ward by way of Gabemichigamme lake, the Kawishiwi river and White Iron lake to 

 Tower, and indefinitely westward. The greenstone hills, known as Twin peaks, south 

 of Ogishke Muncie lake, are the highest summits of this range. Between Ely and 

 Tower are numerous hills belonging to this range. The northern belt of greenstone 

 enters the state from Hunter's island, appearing conspicuously at the south side of 

 Bassimenan lake. At Pipestone rapids and Fall lake it widens southward and appar- 

 ently unites at the surface with the southern belt, the overlying Upper Keewatin 

 being absent for the distance of a few miles. But further 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. In general these greenstone ranges consti- 

 tute topographic elevations, the country being hilly or sub-mountainous, and this 

 character is hightened when granitic intrusion has still further hardened this rock. 



It is in the upper part of the Lower Keewatin that occur the iron deposits at 

 Tower and at Ely. The enclosing rock is obscurely characterized, being in the main a 

 greenstone which sometimes is distinctly fragmental, as at Tower, and sometimes 

 hardly distinguishable from a massive igneous one, as at Ely. Owing to the structure 

 and character of the ore, however, which is believed to be of the nature of an oceanic 

 precipitate, it is quite certain that in all cases where this ore occurs the enclosing 

 rock is a sedimentary one, although composed of the elements of a basic eruptive. 

 This ore is common between Tower and Gunflint lake. 



The fragmental, stratified portion of the Lower Keewatin becomes more 

 important toward the west, while the plainly massive characters seem to fade away. 

 The southern arm, for instance, of the Lower Keewatin, taking the form of more or 

 less stratified greenwackes and finally of graywackes and argillytes, at Tower widens 

 toward the south and continues apparently to the Giant's range of granite, by the 

 advent of which it is changed to crystalline schists. Westward from Vermilion lake, 

 while it is evident, from what is known of the region, that the Lower Keewatin 

 extends as far as the Mississippi river and its northern tributaries and across the 

 Bowstring river, the prevalence of the drift and the Cretaceous is such that nothing 

 is known as to its divisions and geographic limits. Toward Rainy lake it is also 

 apparent that a similar change takes place, i. e., that the fragmental character pre- 

 vails over the igneous. In this direction, further, a very extensive regional meta- 

 morphism has converted the Lower Keewatin into mica schists and gneisses, and this 

 change has been accompanied by the intrusion of large volumes of granite. It is not 



