458 



SHALE. 



Finally, it has been thought necessary to enu- 

 merate among* the shales, that substance known 

 by the name of adhesive slate, which occurs in 

 that peculiar and supposed fresh-water formation, 

 known by the name of the Paris basin. Here- 

 after perhaps, when the similar formations dis- 

 covered in other parts of the world shall be better 

 known, it may become expedient to form a sepa- 

 rate geological division for the purpose of con- 

 taining the rocks that appertain to them. At 

 present, it would be unnecessary, and indeed 

 improper, to attempt such an arrangement ; and 

 the substances found in those of France and 

 England, the only two as yet thoroughly known, 

 must therefore be enumerated with those members 

 of the secondary class to which they bear the 

 strongest affinities. 



The texture of all the shales is more or less dis- 

 tinctly schistose, and many of them also, break ac- 

 cording to certain natural joints, by which they 

 are divided in the beds. In other respects, they 

 present many different aspects, arising from the 

 greater or less fineness of the materials, or the 

 variety of substances which enter into their com- 



