676 



Report of the State Geologist. 



These figures, though large; do not include other shale products, such as 

 sewer-pipe, stoneware, terra-cotta, pressed brick, etc., and as will be seen from 

 them, Ohio and Illinois are the largest producers. The works in these two 

 states have been erected on a large scale, and the products find a wide 

 application. 



Until recently shale was little used by clay workers in the eastern 

 states, but, having become convinced of its value, they are now taking full 

 advantage of it. 



The whole southern half of New York state is underlaid by a formation 

 including among its members many extensive shale deposits. These have 

 been tried with success at several points, and their utilization should expand 

 rapidly in the near future. 



General Properties of Shales. 



A shale is practically nothing more than a hardened clay, having been 

 formed in the same manner, viz. ; as a line sediment deposited in the quiet 

 portions of lakes or seas, but subsequently hardened by burial under other 

 sediments laid down upon it. 



Although shales are apparently very distinct from clay, on account of 

 their rock-like condition, the two materials have practically the same physical 

 and chemical characters, and shale, when ground and mixed with water, 

 possesses the same plasticity as clay. 



Shale-like clay may vary considerably, for just as a clay, by an increase 

 of its siliceous contents, may pass into sand, so a shale, by an increase of 

 sand grains in its composition, may grade into a sandstone. This is not at 

 all an uncommon occurrence. 



Shales may also exhibit another change, viz. ; passing into slate as a 

 result of metamorphisrn. Such slates, when ground and mixed with water, 

 will never have the same plasticity as shale. They also show a false bedding 

 developed as a result of pressure, while the original layers of sedimentation 

 are almost obliterated, the slate showing no tendency to split parallel to them. 



At times shales run so low in impurities that they are adapted for the 

 manufacture of refractory materials. Such shales are restricted almost entirely 

 to the Carboniferous period (in the eastern United States) and are therefore 

 not to be sought in New York state. 



It sometimes happens that shales are so charged with bituminous matter, 

 that this impurity has to be taken into consideration in the process of burning, 

 on account of the enormous heat which it is likely to develop. 



