54 PRIMARY STRATIFIED ROCKS. 
conclusion is the more important, because it has 
been the refuge of some speculative philosophers 
to refer the origin of existing organizations, either 
to an external succession of the same species, 
or to the formation of more recent from more 
ancient species, by successive developments, 
without the interposition of direct and repeated 
acts of creation ; and thus to deny the existence 
of any first term, in the infinite series of succes- 
sions which this hypothesis assumes. Against 
this theory, no decisive evidence has been ac- 
cessible, until the modern discoveries of geology 
had established two conclusions of the highest 
value in relation to this long disputed question : 
the first proving, that existing species have had 
a beginning ; and this at a period comparatively 
recent in the physical history of our globe ; the 
second showing that they were preceded by 
several other systems of animal and vege- 
table life, respecting each of which it may 
no less be proved, that there was a time when 
their existence had not commenced ; and that 
to these more ancient systems also, the doctrine 
of eternal succession, both retrospective and 
prospective, is equally inapplicable.* 
* Mr. Lyell, in the four first chapters of the second volume of 
his Principles of Geology, has very ably and candidly examined 
the arguments that have been advanced in support of the doc- 
trine of transmutation of species, and arrives at the conclusion, 
*< that species have a real existence in nature, and that each 
