180 *HE GEOLOGY OF MIXNESOTA. 



[Sands tones t 



by the dip of the formation as seen at the islands in the river, and at Louis- 

 ville, its true position in respect to the outcrop at St. Lawrence would not 

 be made out correctly. The principal quarries are owned by F. Nicolin 

 and Philip Kipp ; the former opened in 1858 and the latter in 1862. From 

 these quarries was taken the stone used in the construction of the Jordan 

 City mills and the mill of Foss and Wells, at Jordan. The strata are from 

 two inches to two feet in thickness, but cut by rather frequent joints ; still 

 there is no difficulty in obtaining blocks as large as needed for ordinary 

 construction. 



When the rock is taken from below the water level, or from deep exca- 

 vation, it has the gray color of the Dresbach stone, but that put in the Jor- 

 dan City mills is much stained in stripes, parallel with the sedimentation, 

 with iron-rust. This probably renders it firmer, as well as darker, and gives 

 it much the appearance of the rock quarried near Fort Snelling already 

 mentioned (No. 31). The crushing tests that have been made on rock of 

 these two colors from the same quarry (Nos. 33 and 35) show the greater 

 strength of the rusty layers. They also show that the rusty stone absorbs 

 moisture more rapidly, and is easily destroyed by corrosive and other vapors, 

 at least in the case of those portions containing considerable lime and mag- 

 nesia, rendering them less valuable as a building stone. 



Microscopic characters of No. 33. Th!s stone has no greensand grains, or very few ; some of 

 the grains are of orthoclase feldspar ; occasionally a mnscovile scale can be seen ; films of ocher are 

 common, some of them being square, as if the product of changed pyrite. The most of the rock 

 consists of fine quartz grains which are rounded or sub-angular, some of the largest being a fifth 

 of a millimeter in diameter. 



The red sandstone from Fond du Lac, St. Louis county (No. 34), is of the 

 Potsdam formation, and extends along the south shore of lake Superior east- 

 ward, forming the bluffs of the Apostle islands and of the mainland at nu- 

 merous points. At Siskiwit bay, near the west end of lake Superior, the 

 rock No. 39 was taken from it. This rock is of the same formation, pre- 

 sumably, as the quartzyte that has been described near New Ulm and in 

 Pipestone county (No. 12). The layers are tilted, at Fond du Lac, toward 

 the southeast. They are associated with, and overlie, a vast amount of soft 

 red shale which passes sometimes to a shaly red conglomerate, the same 

 that in other places about lake Superior is in contact with the igneous rocks 

 and becomes copper-bearing. This red sandstone is well known in Milwau- 

 kee, Chicago and Detroit. The quarries in it further east furnished the red 



