OLMSTEI) COUNTY. 343 



Trenton limestone.] 



limestone that are eminently fossiliferous, their upper and lower surfaces 

 being frequently studded with brachiopods and gasteropods, as well as 

 encrusted with bryozoans, which stand out in relief, *with only partial or 

 slight attachment to the calcareous mass. 



It has been suggested that the clay derived from the green shales would 

 would make good brick or pottery. The grain is very fine, but the pres- 

 ence of small calcareous fossils injures it for these purposes. A pottery 

 factory, in which this clay was employed, started some years ago, had 

 to be abandoned on this account. 



The limestone strata which have been known distinctively as the Tren- 

 ton, or "Lower Trenton", have a thickness of about twenty feet in Olmsted 

 county, and lie at the base of the Trenton group here described. The up- 

 permost layers of this limestone are frequently interbedded with the green 

 shale above, so' that the transition from one to the other is similar to that 

 from the Galena to the shales overlying. In Olmsted county this limestone 

 is compact, heavy, very firm, resonant when struck with a hammer, frac- 

 turing conchoidally, fossiliferous, and in beds from four to six inches. Its 

 color when weathered is drab, but when deeply quarried it is blue. It con- 

 tains many large cephalopocls, numerous crinoidal stems, remains of tri- 

 lobites (hotel us and Cali/mene), and many brachiopods, including Lingula 

 Elderi, Whit, 



This rock is much quarried, particularly in the vicinity of Kochester, 

 where many foundations and several stone buildings have been constructed 

 from the Trenton quarries near by. The quarry of W. Jenkins just with- 

 in the city limits has furnished a large amount of this stone. 



The Drift. This covers much of the county. It thins out toward the 

 northeast. It is of considerable thickness in the southwest. Its edge is 

 ragged, but its irregularities do not conform with the present drainage 

 system. It consists of a stony blue clay, washed or yellow clay, stratified 

 gravel and sand and boulders. 



The blue, clay is by no means continuous. It is found in limited areas 

 and bands in various parts of the county, and quite generally in the west- 

 ern portions. Sometimes it forms distinct ridges, as in western Rochester 

 city, and in the valley directly east of Rochester. The washed clay, as its 



