152 THE GEOLOGY OF MINNESOTA. 



[Red Quartiyte. 



lie often somewhat displaced. The color is sometimes pinkish, but in the 

 massive portions it is also purplish. When it is brick-red the strata are apt 

 to be thin and also more aluminous. 



At Sioux Falls, in Dakota, this rock has one of its characteristic out- 

 crops, not only being the cause of the water-fall but presenting perpendicu 

 lar walls between which the river flows for some distance before it roadies 

 the falls. The rock here dips six or eight degrees toward the south. The 

 beds are purple within, especially the thick ones, but toward the outside and 

 along the joints they are changed in color to a rose-red, or to a pinkish red. 

 None of the brick-red, heavily iron-stained color can be seen. The effect 

 produced by weathering not only changes the color but also the hardness, 

 so that the rock goes into a loose sandrock again and crumbles in the hand. 

 This occurs to so large an extent that in suitable places it is gathered and 

 used for mortar. There are also some beds that are now wholly (so far as 

 can be seen) in this friable condition. The sand that results is a pure silica, 

 nearly white, and translucent, though it is apt to show at h'rst a slight 

 pinkish tint, arising from the remains of the cement among the grains. 

 There is visible here, of the bedding, a thickness of about fifty feet, and the 

 river goes over the beds from south to north, producing a fine water-power. 

 At the quarries the regular strata are from six to eighteen inches thick. 

 Some of the beds are purple, but that color seems to fade out gradually, 

 passing through the "fawn color" of the Kasota stone of this state, to a 

 light pink sandrock. The county jail at Sioux Falls is built of this rock, 

 also the Queen Bee flouring njill, and it is being employed exclusively in the 

 territorial penitentiary at the same place. It is used at Omaha, Nebraska, 

 for street paving, under the name of " Sioux Falls granite." 



For ornamental purposes this rock has not been much employed. It 

 will take a perfect polish, owing to its large content of free quartz, and will 

 retain it longer than any granite. Small ornaments have been made of 

 some of the richly colored strata, and sold under the name of "jasper", and 

 some monumental bases have been constructed of it. The strata are very 

 regular and firm, but at the same time are broken with a heavy sledge at 

 the quarry. They break at random, and those blocks which happen to pre- 

 sent a face suitable are used for range-work in the wall, the remainder 

 being needed for filling and for the back-side. 



