564 



CHERT. 



THE rock, which, according to the views al- 

 ready held out, I have introduced into the present 

 arrangement by this name, is so like, in most 

 cases, both in external aspect, and in its chemi- 

 cal characters and composition, to the mineral 

 called chert, that it seemed better to adopt that 

 term than to invent a new one. 



Its analogy in origin to the two preceding 

 rocks, no less than the convenience of the student, 

 was the inducement to give it a place ; as it was 

 impossible to consider it as a variety of those 

 limestones, or sandstones, with which it is par- 

 ticularly connected. The reader will easily dis- 

 cover that it is mentioned in the writings of 

 Saussure, although he has not traced its true 

 affinities as if he had been fully aware of their 

 nature. 



To describe the geological connections of 

 this rock, would be to repeat much of that which 



