290 GEOLOGY OF EASTERN WISCONSIN. 



Economic Considerations. The greatest prospective value of 

 this formation is doubtless its water-hearing capacity, it being, as has 

 already been shown, the great source of Artesian fountains in this 

 portion of the state. In view of this fact, the foregoing developnients 

 in respect to its nature possess eminent practical importance. 



For some years geologists have habitually recommended the sand 

 of this formation for the manufacture of glass. Its value for that 

 puri)ose is now being put to the practical test. A factory has recently 

 been established at Omro for that purpose. The sand is derived from 

 near Waukau. A six pot furnace has been erected having a capacity 

 per month of 800 boxes of 100 feet each. At present the manufacture 

 is confined to window glass and shades. The results thus far attained 

 are reported as highly satisfactory. 



In the town of Waterloo the sandstone has sufficient compactness 

 to serve as a building stone, but usually it is too soft. This latter fact, 

 however, perniits its extensive use as sand for mortar, and similar 

 purposes. At most localities it can be dug with pick and shovel, the 

 mere handling being sufficient to reduce it to sand. On account of 

 its cleanness and sharpness, it is much superior to most drift sand. 



TRENTON GROUP. 



Upon the St. Peters sandstone there lies an extensive series of lime- 

 stones and shales, which represent the Trenton period. It consists of 

 three main divisions, which are recognized in geological history as 

 epochs. The lowest member is known as the Trenton limestone, the 

 Uext in order as the Galena limestone, and the uppermost as the Cin- 

 cinnati shales and limestone. These are firmly linked together by fos- 

 sils common to the three horizons, and in the northeastern part of the 

 state it is exceedingly difficult to discern any satisfactory line of de- 

 markation between them. In the southern portion, however, they arc 

 well distinguished, and will receive consideration in the order named. 



TRENTON LIMESTONE. 



Subdivisions. The Trenton limestone proper, as it is developed 

 in the southern portion of the district under consideration, consists of 

 four subdivisions sufficiently well characterized to be valuable aids in 

 the study and discussion of the formation, and in the practical appli- 

 cation of the results of the survey. 



Adhering as closely as the nature of the case will admit, to the 

 terms already in use, these will be distinguished as follows: 



