PREFACE. 
Vll 
111 the descriptive part of the work, the 
reader will perceive, my aim has been to apply 
to extraneous fossils the mode of investigation, 
happily established in Botany and Zoology. 
Hence, instead of giving a mere list of names, 
and these chiefly of species formed from entire 
genera or tribes of organic bodies’'^, I consider, 
in the first instance, every genuine or permanent 
fossil species to depend on a single recent one ; 
and, accordingly, have endeavoured to fix the 
essential characters, by which it may hereafter 
be discriminated. 
In arranging and describing petrifactions 
on this plan, I have unavoidably been led to 
use certain distinctive terms, which either do 
not occur in works of this kind, or not exactly 
in the sense in which they are here employed — 
of these, it was at first my intention to have 
given an explanation in the present volume ; 
* V. Ginel. Syst. Nat. T. Ill, Append, p. 385. Also most other Systematic 
Arrangements of extraneous fossils. 
