178 THE GEOLOGY OF MINNESOTA. 



[Sandstones. 



exterior, and renders the tall piers of the Fort Snelling bridge an object of 

 admiration to all architects. 



The sandrock quarried at Dresbach, in Winona county (No. 32) is largely 

 feldspathic, and rather soft, but it becomes harder on the drying out of the 

 water which it contains in the quarry. It belongs to the St. Croix forma- 

 tion and very near its lowest part. The great anticlinal of that formation 

 crosses Winona county, bringing to view lower strata of the St. Croix than 

 can be found along the Mississippi in any other county in that part of the 

 state. These lowest beds cannot be found in the Mississippi bluffs further 

 south, nor north. They probably might be opened in numerous places in the 

 valley of Koot river and its tributaries, in Houston and Fillmore counties, 

 in the direction of the anticlinal, which enters the state from Wisconsin. In 

 the valley of Black river, at Black River Falls, thirty-three miles from the 

 Mississippi, east of Winona, the crystalline granites and schists appear, 

 brought to the surface by this anticlinal. 



The stone is evenly granular, gray, and of a medium-sized grain, very 

 much resembling the Berea sandstone of Ohio. It is in beds that are quar- 

 ried out from six inches to three or four feet thick. It is free from nodules 

 of pyrite or of coarse quartz pebbles. It can be sawn easily, and dressed 

 with great facility with a hammer and chisel. Its strength in crushing 

 pressure is 6,500 pounds per square inch when placed on its bedding plane, 

 and 3,750 pounds when placed on its edge. Though ranking somewhat 

 lower than the Berea stone in that respect, it will become stronger as the 

 quarries progress, the present working not having penetrated beyond the 

 effects of long weathering, while the stone from the Berea quarries with 

 which it has been compared was from old and much used quarries where 

 the stone shows its best estate. Its strength is ample for the largest struc- 

 tures, and its durability under the weather is evinced by tne projecting 

 terrace-like shoulder which it causes along the base of the Mississippi 

 bluffs. Its naturally gray color is found at a depth of a few feet from the 

 weathered surface, the weathered and faded condition of the same strata 

 being seen in the quarries at Dakota (No 36) about a mile above Dresbach. 

 It then becomes lighter, both in weight and in color, absorbs moisture 

 much more readily, is more affected by freezing and thawing, and also is 

 less able to maintain itself intact in case of fire followed by water thrown 



