LIMESTONES. 



321 



TABLE 147. 

 ANALYSES OF PURE CHALKS USED IN AMERICAN CEMENT-PLANTS. 



TABLE 148. 

 ANALYSES OP CLAYEY CHALKS U<?ED IN AMERICAN CEMENT-PLANTS. 



Examining chalk deposits.* The chalk deposits of most of the 

 States have been carefully mapped by geological surveys/ and much 

 time will be saved by procuring and studying the proper reports. These 

 will give general data on the distribution and character of the chalk 

 formations. 



In examining chalk deposits it is well to recollect that they are always 

 found in thick and almost horizontal beds. Stream ravines usually 

 give good natural sections, which will serve to give a preliminary idea 

 of the character of the rock. In securing samples, the earth-auger 

 gives satisfactory results in most chalk deposits, because the material 

 is usually soft enough to be penetrated readily by this tool. 



The principal impurities to be guarded against are nodules of pyrite 

 and grains of sand, both of which are very common in many American 

 chalk deposits. 



* See pages 315-318 for further notes on this subject. 



