RAW MATERIAL: NATURAL-CEMENT ROCK. 



219 



Excavation of the Rock.* 



In excavating a natural-cement rock the preferable method of working, 

 so far as cheapness u concerned, is quarrying. But so many of the 

 natural-cement beds now worked are thin (from 4 to 8 feet in total 

 thickness) or occur in such steeply inclined positions, that a surprisingly 

 large percentage of the raw material is obtained by mining. In the 

 Rosendale district of New York, for example, mining is the common 

 mode of extracting the rock; and the same is true of the plants in the 



cj 



FIG. 35. Loading cars, Speed quarry, Speeds, Ind. 



Akron district, New York, of those in Maryland, North Dakota, Illinois 

 and Kansas, of the Howard plant in Georgia, and of many of the Louis- 

 ville district plants. The plants of the Milwaukee district, the Rossville 



* Further details concerning quarrying costs and methods will be found on 

 pages 367-381. 



