1852. ] OF THE ROYAL INSTITUTION. 195 
connect the fact of its disappearance with the evidences of physical 
changes. 
[The Lecturer illustrated these points by diagrams and special 
demonstrations, selecting for explanation two local cases, the one 
marine and the other fresh-water; the former taken from the 
geological phenomena of Culver cliff and the neighbouring bays in 
the Isle of Wight, of which a beautiful and original model had been 
communicated by Captain Ibbetson for the purpose, and the latter 
from his own recent researches (unpublished) on the succession of 
organic remains in the Purbeck strata of Dorsetshire, conducted as 
part of the labours of the Geological Survey of Great Britain. ] 
The second and more indirect source of the notion of the life of a 
species may be traced in apparent analogies, half-perceived, between 
the centralization of generic groups in time and space, and the 
limited duration of both species and individual. But in this case 
ideas are compared which are altogether and essentially distinct. 
The nature of this distinction is expressed among the following 
propositions, in which an attempt is made to contrast the respective 
relations of individual, species, and genus to Geological time and 
Geographical space. 
A. The individual, whether we restrict the word to the single 
organism, however produced—or extend it to the series of 
organisms, combined or independent, all being products of a 
single ovum—has but a limited and unique existence in time, 
which short as it must be, can be shortened by the influence of 
unfavourable conditions, but which no combination of favouring 
circumstances can prolong beyond the term of life allotted to it 
according to its kind. 
B. The species, whether we restrict the term to assemblages of 
individuals resembling each other in certain constant characters, 
or hold, in addition, the hypothesis (warranted, as might be shown 
from experience and experiment), that between all the members of 
such an assemblage there is the relationship of family, the 
relationship of descent, and consequently that they are all the 
descendants of one first stock or protoplast (how that proto- 
plast appeared is not part of the question) — is like the individual 
in so much as its relation to time are unique: once destroyed, it 
never reappears. 
But, (and this is the point of the view now advocated) unlike 
the individual, it is continued indefinitely so long as conditions 
favourable to its diffusion and prosperity —that is to say, so long 
as conditions favourable to the production and sustenance of the 
individual representatives or elements are continued coincidently with 
its existence. 
[No amount of favouring conditions can recal a species once 
destroyed —on this conclusion, founded upon all facts hitherto 
observed in palzontology, the value of the application of Natural 
History to Geological science mainly depends. ] 
