LETTER XVIII. 



197 



and forcible statement of it by Professor Powell. It 

 is as follows : — 



*' Throughout all formations, the grand truth to which every 

 accession of geological discovery bears witness in a more 

 remarkable manner, is the principle of unity of plan continuall}^ 

 exemplified in all the varieties of organic structures disclosed. 

 Even the most seemingly monstrous and incongruous forms of 

 animated existence in times past are all, without exception, 

 constituted according to regular modifications of a common 

 plan, and with parts, organs, and functions related by the 

 closest analogies to each other; so that n) sooner is a new 

 specimen detected than it immediately finds its proper posi- 

 tion in the scheme of nature ; no sooner is a new form dis- 

 covered than it is instantly assimilated with some known type, 

 and found to hold an assignable place in the system. Whether 

 a given organic fossil (as in some instances in more recent 

 beds) exhibit characters difiering from some known form onl\^ 

 as a variety or sub- species, or whether (as in earlier cases^ it 

 present features unknown to any existing genus or order, or 

 ("as in other instances) offer conditions in any degree inter- 

 mediate, still in all cases alike the remarkable point is always, 

 that a place and a name can be immediately assigned to every 

 new form as it presents itself ; and this too invariably in such 

 a manner that it either tends to supply a link in affinity between 

 orders of being already related, or indicates some new and 

 unexpected point of analogy. There is never any deviation 

 from system and regular plan ; we never light upon a fossil 

 centaur or palaeozoic mermaid ; there never occui's any junction 

 of heterogeneous members, any real departure from type and 

 system. The invariahleness of the results through such enormous 

 series of ages cannot but impress the mind, when duly considered, 

 with the highest idea of the preservation of continuity ^ * 



* Essays. Ess. III. — On the Philosophy of Creation, ipi^. S37-S. 



