368 CEMENTS, LIMES, AND PLASTERS. 



ing. If marls be included, the percentages excavated by the different 

 methods would probably be about as follows: quarrying, 88 per cent; 

 dredging, 10 per cent; mining, 2 per cent. 



Stripping. When a limestone is being quarried, the opening should 

 be so located as to give as little stripping as possible in proportion to 

 the available rock; for in this case the stripping is merely dead work, 

 adding greatly to the expense of the product. In dealing with a shale- 

 bed, the " stripping" is usually merely weathered shale and can be 

 used as well as the harder portions of the deposit. 



FIG. 71. Stripping a flat, shallow bed. 



A very thick bed of limestone, or a bed of moderate thickness lying 

 almost horizontally, will not give as much stripping per ton of good 

 rock as a thin bed or a bed dipping at a high angle. In handling com- 

 paratively thin earth stripping in flat country, scrapers or excavators 

 may be used (Fig. 71); while at one cement-plant a heavy soil cover 

 on a quarry near a river-bank is removed by hydraulicking. This last 

 process is also used in several large brick-plants. 



Quarry practice. In most of the quarries for cement rock or lime- 

 stone, the rock is opened up on a low side-hill, so as to give a long work- 

 ing-face with light stripping and as little grade as possible in the work- 

 ings. The rock is blasted down in one or more benches, according to 

 the height of face exposed, and the larger pieces are sledged or reblasted 

 to manageable size by men placed along the working-face. It is then 

 loaded either into one-horse carts or into small cars running on tem- 

 porary tracks laid close up to the face. In the former case the carts 

 are driven to a dump and loaded into cars; in the latter case the cars 

 are drawn by horses or pushed by men to a turntable. This turntable 



