172 THE GEOLOGY OF MINNESOTA. 



[Limestones. 



Cromer, was opened in 1865, but was not much worked till 1867. The beds 

 quarried attain an aggregate thickness of about twelve feet and an indi- 

 vidual thickness of a few inches to three feet. They are easily wrought, 

 and have been extensively used at Faribault where the principal buildings 

 have been constructed of them. The uppermost stratum, which is about 

 eight inches in thickness, has been termed "marble", and some ornamental 

 pieces have been cut from it. It is susceptible of a fine and uniform polish, 

 has a compact texture and gray color. The polished surface shows vari- 

 ous markings due to the contained fossils, but its composition and origin 

 are the same as the other strata, except that it probably would be found 

 on analysis to contain more carbonate of magnesia. At Faribault the fol- 

 lowing structures were made of this stone, though not perhaps wholly from 

 this quarry: the state asylum for the deaf and mute, the Shattuck school 

 and surrounding buildings, the Episcopal church and the public school- 

 house. 



Some of the stone used in construction at Northfield, in Rice county, is 

 from the same place (Cromer's), but the quarries opened in the valley of 

 Prairie creek, in the eastern part of the same county, supply a stone of the 

 same kind and equally good. Here are numerous quarries, but they are not 

 wrought so extensively as those near Faribault. Willis hall, of Carleton 

 college, is built of the Trenton quarried near Dundas, the sills and caps of 

 the doors and windows and the steps at the entrance being from the Fari- 

 bault quarries. 



Microscopic characters of No. 26. Throughout the section can be seen the forms of sections of 

 fragments of fossils. They are characterized by a transparency that is not seen in the rest of the 

 rock, due to the pure and crystalline condition of the calcite that constitutes them. It seems as 

 if much of this rock were derived from comminuted shells and corals, since it cannot be resolved 

 into granules that show individual crystallization, but rather remains an amorphous or confused 

 substance through which, at crossed Nicols, a few isolated rays of light can be seen to penetrate. 

 It has scattered particles of pyrite. 



Microscopic characters of Nos. 27 and 28. Most of this rock, at least the compact calcareous 

 portions, is exactly like the rock from Fountain. The figure (Fig. 4 on plate C) shows dissemi- 

 nated crystals of calcite in the general amorphous mass of calcareous matter, somewhat in the 

 manner of porphyry, drawn from a section of the rock from St. Paul, and magnified forty dia- 

 meters. 



The quarries in the Trenton limestone at St. Paul are on both sides of 

 the river. The principal owners are Wm. Dawson, A. Gotzian, Breen and 

 Young, M. Roche, Wm. Zollman and W. F. Davidson. The rock lies hori- 

 zontal, in beds that vary from a few inches to about two feet in thickness, 



