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NEW YORK STATE MUSEUM 



office is the only one in which this rock has been quarried to any 

 extent. Being of a rather coarse grain, it serves well for founda- 

 tions and will dress readily. Some of the beds are of sufficient 

 thickness to form good blocks. The strata immediately above this 

 bed are quarried a short distance south by Mr Yronian, the rock 

 having been used for foundation in the new Schoharie schoolhouse. 

 Somewhat higher up in the field the higher Rondout beds are 

 taken out. The only locality where the Eondout waterlime is 

 extensively quarried in this region is at Howes Cave, where the 

 Helderberg Cement Company uses this rock for the manufacture 

 0|f natural or Rosendale cement. The stratum used lies just above 

 the Cobleskill and is six feet thick. An analysis of this lime- 

 stone gave : a 



Lime carbonate 55.17 



Magnesium carbonate 19.71 



Silica 12.89 



Ferric oxid and alumina 11.15 



Water 66 



Loss 12 



Total 100. 



At this locality the beds immediately succeeding the cement 

 bed and for nearly 50 feet above it are not utilized. Above this 

 about 36 feet of Manlius and about 30 feet of Coeymans occur. 

 These are quarried together and manufactured into Portland 

 cement. While the natural cement rock has been used for a long 

 period of time for the manufacture of natural cement, the Tort- 

 land cement industry only began here in 1898. It was com- 

 menced on a small scale, but rapidly grew as the demand for 

 Portland cement increased. In 1900 a new plant with a nominal 

 capacity of 1500 barrels a day was erected. The process of manu- 

 facturing the cement is as follows: 



The limestone is crushed and mixed with the proper amount of 

 clay in the presence of water by what is known as the " wet 

 process". This is done in cylindric tanks in the center of each 



^lies. N. Y. State Mns. Bui. 44, p. 817. 



