MORRISON COUNTY AND GRANITE AREAS 857 



Morrison County exposures, glacial drift covers the schists, as remarked 

 in the mention of the Brainard deep well {ante, page 345). 



Taken as a whole, Morrison county, in its content of rock types among 

 the ancient crystallines, is among the most diversified areas of the state. 

 The range of granitic rocks represents several varieties, and gneisses in 

 the eastern part of the county are important. Gabbros, diorites, and 

 diabases appear in unexpected force to the west of the Mississippi river. 

 Finally extensive belts of hornblende-biotite schists are seen to cross the 

 course of the river, locally loaded with staurolitic crystals and garnets, 

 while in the more disturbed areas lenses of a peculiar hornblendic 

 quartzose habit appear, of sufficient lithologic interest to receive the 

 name quartz-diorite from Doctor Kloos. 



Granite Areas 



Throughout a large area in Benton, Sherburne, and Stearns counties 

 the rocks are, so far as seen, wholly granitic. There is considerable vari- 

 ation in texture, color, and chemical composition. An acidic type pre- 

 vails, represented by the Le Sauk granites, with 74 per cent of SiO.^. A 

 heavy proportion of quartz is in such varieties. Again the per cent of 

 Si02 sinks nearly to 69 per cent. Here the proportion of quartz is small 

 and the color prevailingly dark. These characters correspond with a 

 heavy proportion of hornblende as the bisilicate constituent. 



A discussion of these granite areas is without the scope of this paper. 

 Their presence along the Mississippi is mentioned chiefly to enforce the 

 westward extension of the area believed to be Keewatin, which stretches 

 from the ■ city of Duluth southwestward even beyond the central por- 

 tions of the state. 



LiTHOLOGY OF THE SeRIES 

 THE PROBLEM PRESENTED 



The effort is made in the following pages to trace a petrographic and 

 genetic relationship between the carbonate schists, graywackes, and 

 graywacke slates of Thomson, Carlton, and Cloquet, and the thoroughly 

 crystalline dolomite, biotite, and hornblende-biotite schists as repre- 

 sented along the Mississippi, Snake, and Kettle rivers, in the several 

 localities enumerated on the preceding pages. Such a relationship is 

 not infrequent in this part of the continent. 



OTHER LOCALITIES CITED 



Fifteen years ago Van Hise^ traced out and established the relation- 



* C. R. Van Hise : Upon the origin of the mica-schists and black mica-slates of the Penokee 

 Gogebic iron-bearing series, Amer. Jour. Sci., vol. xxxi, 1886, pp. 453-459. 



