OLMSTED COUNTY. 34 \ 



Galena limestone.] 



cavities are found. Under the influence of the weather the rock is seen to 

 vary in solubility. The result is frequently sink-holes of varying dimen- 

 sions. Such holes, a few feet deep, are common on the bluffs of this form- 

 ation. Another result of this unequal weathering is the craggy appear- 

 ance of the bluffs formed by the Galena. 



This limestone is well displayed in this county at Thomas Garrick's 

 quarry, sec. 18, Rochester township. The floor of this quarry is about 

 thirty feet above the Trenton. To the top of the quarry is about thirty- 

 five feet. The rock is a sparry, magnesian and more or less arenaceous 

 limestone. It is in beds one to three feet thick, separated by very thin 

 layers of light blue shale. The beds are massive and yellowish, somewhat 

 stained with iron arising from the decay of iron* pyrites. The upper por- 

 tions are most arenaceous and fossiliferous. In the crevices is found abun- 

 dance of satin spar, and in the largest ones stalactites may be found. 



R. Williams's quarry, on the north bank of Root river, sec. 31, High 

 Forest, is in this formation. This rock is exposed for twenty-five feet, and 

 is dolomitic, more or less concretionary, with small, spar-lined cavities. 

 It is sparingly fossiliferous. The upper six feet are much broken up. The 

 remainder is compact and unevenly bedded. The concretionary structure 

 is not visible on fresh surfaces. It is brought out by weathering and espe- 

 cially by burning, and then appears in the form of fine rusty lines. 



On the left bank of the same stream, about one mile west of Williams's 

 quarry, is an exposure of yellow' thin-bedded, broken, uneven, dolomitic 

 limestone, of which only eight or ten feet are visible. 



The same rock is well exposed in the ravines of Salem and Rock Dell, 

 where it is quarried to some extent for building. 



As to economical value, this formation produces one of the best building 

 stones found in the state. It is much used in Rochester, but has been 

 mostly derived from Mantorville, in Dodge county. It will be further de- 

 scribed in the report of that county. At Russell Williams's quarry near 

 High Forest it is burned for lime. 



Below these magnesian strata there is an interval occupied with more 

 or less shale, or with alternations of shale with limestone. At the same 

 time the limestone loses its distinctive lithological characters, and its mag- 



