834 NEW YOEK STATE MUSEUM 



common metliod is to mine out the cement rock, leaving great 

 pillars to support tlie roof (pi. 75-77). The opening along the 

 outcrop may at times be nearly 1000 feet long. Some idea of 

 the method of mining may be gained from the plates. 



Great falls of rock sometimes occur (pi. 78) around the entrance 

 to the abandoned workings. The bed is commonly worked down 

 on the dip, and the slopes are sometimes 800 or 1000 feet long. 



The following table gives the number of firms in this region, 

 and other details concerning their mines, taken from F. L. 

 IsTason's report. 



The method of manufacture is well illustrated by the following 

 description of the works of the Lawrence cement co., which have 

 a capacity of 5300 barrels a day. The rock used is taken from 

 two beds, known as the upper or light rock and lower or dark 

 rock. The two are mixed and broken into a suitable size for 

 charging into the kilns. These kilns are of stone, lined with fire 

 brick. Alternate layers of anthracite coal and cement rock are 

 charged into the kiln, a layer of wood being placed at the bottom 

 to light the fire when the kiln is first started. 



Each day the burned materi&l is removed from the bottom of 

 the kiln, while fresh fuel and green rock are introduced at the 

 top. The material drawn contains a certain amount of under- 

 burned and overburned rock, the former going back to the kiln, 

 while the latter is thrown away. The normally burned rock is 

 taken to the " cracker " room, where it is crushed in crackers to 

 fragments and grains, varying from dust to hickory nut size. 



