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



graphic feature, are due in a large measure to jointing. The jointing 

 which has developed along the bedding, constituting the major struc- 

 ture on the southward slopes and a system of fractures in which there 

 are frequent evidences of shearing, give character to the northward 

 slopes. 



Aside from the major structures, there are minor ones which var}^ with 

 the condition of the rock. 



Several efforts have been made at Thomson and near Cloquet to quarry 

 roofing slate. The color is black, weathering to a light gray. The layers 

 of slate, intercalated between corresponding layers of quartzite schist, are 

 from 1 to 5 feet in thickness. Each layer is cut by many joints into 

 plates. These joints, always striking with the rock or within 10 to 20 

 degrees of the same direction, make an angle of 30 to 40 degrees with 

 the bedding planes, which at the slate quarries in Thomson dip south 

 at from 65 to 75 degrees, and at Cloquet are nearly vertical. For several 

 hundred feet the slate has been worked out, but a persistent war[)ing 

 renders the product of inferior quality (see plate 31, figure 1). 



The Blackhoof Valley 



Around Atkinson are several outcrops of quartzit^i schists. The strike 

 is north 70 degrees east, magnetic, and the dip south at an angle of 65 

 degrees. Farther southeast the dip, continuing southerly, drops to 

 about 25 degrees. The rocks locally assume a decidedly contorted con- 

 dition. The exposures are not numerous, but the rocks lie only a short 

 distance below the surface, and u})on these an a))undant and excellent 

 water supi)l3'^ is always found. 



The rocks separate freely along the schist planes, and are cut into 

 somewhat rhombic blocks by a double system of joints, one of them 

 being nearly coincident with the dip. A light and cheerful slate-gray 

 color characterizes the more t3''pical exposures. The freshly cleaved sur- 

 faces are quite lustrous. As these schists merge into a softer talc-like 

 condition, as is the case where the concretionary lenses of quartz or 

 quartz and siderite occur, the color becomes still lighter, or dark even 

 to blackness. At one exposure, graphite was noted along the cleavage 

 banks. To this source the black color sometimes aeen is referred. 



Some years ago explorations for gold were prosecuted along belt of 

 quartz veins which resulted in finding only small traces of the metal. 



In section 31, township 48, range 17 west, and section 36, township 

 48, range 18 west, there occurs a belt of quartz veins. They vary in 

 direction and lack in continuity ; they occur as a succession of strings 

 and bands, corresponding quite closely in position with the foliation of 



