PREFACE. 



vii 



with propriety, make a part in the specific discri- 

 mination of an earth, metal, &c. It is true, accor- 

 ding to the positions with which we set out, an 

 extraneous fossil exists only in form : take away 

 such form, or consider the fossil to be independent 

 of such form, and it becomes identical with mineral 

 matter But still, to describe the organic structure, 

 as characteristic among the external appearances of 

 a given mineral, is nearly the same, as to consider, 

 in a plant or animal, the accidental variations of 

 figure, received by impression ( g ) from some exter- 

 nal body, as distinctive, and add them to the cha- 

 racter and description of the species. 



It is proper in this place to remark, that the 

 principles now assumed will necessarily bring under 

 the study of extraneous fossils some few bodies, 



without destroying its identity Such is the inorganic structure in 

 minerals ; for if we destroy one or more modifications of this 

 form, some other will remain, as long as the matter itself exists 

 But we may obliterate every vestige of the organic structure in 

 a fossil, and the matter remain the same. This is, therefore, an 

 accidental or adventitious form in fossil matter, if we consider 

 such matter as a mineral species. 



() Corals, shells, and funguses, arc sometimes impressed 

 with the form of the bodies to which they happen to adhere. 



