40 



CHAP. II. 



ON THE MEANING IN WHICH THE TERM ROCK IS 

 HERE USED, AND ON THE GENERAL PLAN OF 

 THE PRESENT ARRANGEMENT ; WITH RE- 

 MARKS ON THE NOMENCLATURE ADOPTED. 



THE compilers of systems have been divided re- 

 specting the substances to which the title of rock 

 should be applied. By some, even metallic ores 

 have been included in this term ; by others, the 

 simple rocks have teen excluded, as belonging 

 to a system of mineralogy. It is unnecessary to 

 enter critically into an examination of these, or of 

 other differences of opinion that have prevailed ; 

 nor is it easy to frame any definition of a rock 

 which is not open to objection. As the object of 

 the arrangement is utility, not logical refinement, 

 it is equally unnecessary to attempt such a defi- 

 nition. There is an evident impropriety in ad- 



