ON A NATURAL SYSTEM 



volcanic productions into clafles agreeable to 

 their principles ; and that all thofe heterogene- 

 ous fubitances, whole combination is viiibly me- 

 chanical, mould be the fubjecl of ths iiril ap- 

 pendix. 



Or GENERA. 



LXIII. Arrangement of Genera. 



BY the afliflance of clafles, all thofe foflils arc 

 connected, whole compofition, charader, and 

 properties are perfectly limilar. Genera require 

 a nearer affinity ; fpecies a refemblance flill clo- 

 fcr ; and varieties mall correfpond in their inter- 

 nal habitudes only. 



Foflils entirely homogeneous are of very rare 

 occurrence; as, for the molt part, two, three, 

 or more principles, enter into their compofition. 



The more innple their competition, it follows, 

 they will be the ealier reduced to their natural 

 genera. 



,Let A and B be the proximate principles of 

 any foflil, let A be heavier than B, the com- 

 pound A B, will be then referred to the genus 

 of A ; but this admits of various exceptions. 



Suppofe B pofleiled of a generic difference, 

 and that it is no where found in a fmgle ilate, 

 (for we do not here fpeak of artificial feparati- 



* on,) 



