OLMSTED COUNTY. 339 



Trenton period.] 



having been made for dip and atmospheric change, the value of 111 feet 

 was obtained for the thickness of this formation. 



The lithological character of the St. Peter is uniform and simple. It 

 is a rather coarse, friable sandstone, pure white except where contam- 

 inated by foreign substances or percolations from the formation above. 

 It contains no fossils so far as could be seen in this county. 



This formation is useful in several ways. When with a tight, magne- 

 sian floor, it holds water, and furnishes a good supply to wells. It is some- 

 times excavated where it comes out on the face of a bluff. Excellent 

 cellars, dry and of uniform temperature, are thus formed, which are used 

 especially for the preservation of vegetables. In the rear of the second 

 Insane Asylum at Rochester is a fine root-cellar in the St. Peter sandstone. 

 Mr. W. D. Hurlbut, of the same place, has an extensive silo embracing over 

 150 feet of chambers, wholly excavated in this rock. It supplies an inex- 

 haustible amount of pure white sand, round-angular, and excellent for 

 mortar or glass-making. 



The rocks of the Trenton period. The highest rocks, stratigraphically 

 considered, belonging to this series are found at High Forest, and at two 

 miles west of High Forest. These are shaly, both aluminous and arena- 

 ceous, sometimes indurated and bedded and sometimes easily crumbling. 

 On sec. 35, Rock Dell, they appear along Root river, having a light buff color, 

 breaking like a hard shale, sometimes arenaceous, even so much so as to 

 become a coarsely arenaceous white sandstone, and at other times some- 

 what calcareous, with a very fine grit, worthless for lime and for all other 

 uses. It was tested for quick-lime by Mr. Brewer some years ago. In the 

 winter it is cracked to pieces by frost; bedding never more than four inches 

 thick, some of it very thin and clayey. The total thickness seen here is 

 about ten feet, but at High Forest, at the quarry of Russell Williams, this 

 shale is seen overlying a body of limerock which at the village rises into per- 

 pendicular bluffs twenty-five to forty feet high, and is extensively quarried 

 for building purposes. In this shale no fossils have been found at High 

 Forest, except an indistinct valve of a small brachiopod like Lc[)1(t')iasericea, 

 but reminding one of the Spirifer family by its eared extremities and its 

 1 leaked hinge-line. The shale here so far as seen amounts to fifteen feet, 

 contains no lw<h of white sandstone, but is gritty and even arenaceous. If 



