366 C. W. HALL — KEEWATIN OF EASTERN AND CENTRAL MINNESOTA 



north 10 to 30 degrees east, thus showing a strong deflection southward 

 from the general direction around Carlton and along the Kettle river 

 and its tributaries. The dip in places is northwestward — 70 degrees at 

 Swan river, 65 degrees at Muncys rapids, 70 to 75 degrees at Pike rapids, 

 very nearly vertical at Little Falls, and finally, at the mouth of Little 

 Elk river, the most northerl}'- point where exposed, the dip varies from 

 vertical to 80 degrees southeast, while the strike is north 40 degrees east, 

 a notable variation from that at Little Falls. Quartz veins usually onl}'' 

 an inch or two in width, lenticiilar masses of " quartz diorite," the oc- 

 currence locally of numerous staurolitic crystals from a lialf inch to ' 

 two inches long, with numerous garnets occasionally filling the matrix, 

 are the chief structural characters of interest. It is to be noted that 

 these are characters peculiar tb contact phenomena. Microscopically 

 the typical rock is a biotite schist. A specimen from Pike rapids, one 

 of the finest exposures on the Mississippi river, shows a groundmass of 

 finely crystalline quartz grains with much coarser folia of biotite plenti- 

 fully distributed. Crystals of staurolite and garnet are numerous, the 

 former up to an inch in length scarcely differentiated from the quartz of 

 the groundmass of the rock, while the light })ink garnets are also full 

 of quartzose inclusions. They seem to have rejected every other mineral 

 save quartz in their cr3^stallization. At the surface the biotite has under- 

 gone that ])hysical change which in reflected light results in the lustrous 

 golden yellow color so frequently observed in decaying drift boulders, 

 namely, the deposition on the cleavage folia of films of iron oxide. 



THE LIMESTONES 



These rocks ofler a wide range of varietal characters. In the creek to 

 the north of the high exposures of fibrous hornblende schist southwest 

 of Sturgeon lake, the limestone is remarkably free from mineral impur- 

 ities. The texture is fine, color a clear, delicate pink, and structural 

 planes distinct. The other exposures are less clearly carbonates. Where 

 the abandoned gorge occurs, the rock gives ever}^ evidence of profound 

 alteration. The surface is disintegrating mingled silicious and calcare- 

 ous material in which the residual is a mass of incoherent quartzose 

 fragments. Beneath the surface the rock is firmer; within 3 or 4 feet it 

 is quite coherent and appears to be a mass of quartz grains of clastic 

 habit imbedded in a matrix of dolomite. The contortion seen in the 

 rock is apparently due to alteration under great pressure with more or 

 less shearing. There is ferric oxide enough in all these layers in which 

 the carbonates occur to give the red color to the rock on exposure. 



An anal3'^sis made by Mr Levi B. Pease, of the University of Min- 

 nesota, of the samples which, both to the unaided eye and under the 



