£30 M. Brongniart on Fossil Organic Remains , Sfc. 
ture are necessary, phenomena much more general, and periods 
of time much more considerable. In the course of a few days, 
the deposits of Calabria have experienced derangements similar 
to those which we see in the beds of the Alps ; and, during a 
space of five or six thousand years, the organised species have 
not manifested any appreciable changes in their forms, or other 
qualities. 
I do not, however, say, that the characters taken from the 
relative disposition of beds (but not from the evident super- 
position ), from their nature, &c., should not be employed, even 
with confidence, by the geologist, in determining the different 
periods of formation. Whether single or united with those 
which are derived from the nature of fossil organic bodies, they 
are of the greatest validity ; but I merely think, and I believe 
I have given strong reasons for my opinion, that when these 
characters are in opposition to those which may be taken from 
the presence of fossil organic bodies, these last should have the 
preference. 
I do not deny that much attention and discretion are neces- 
sary to be used in such a matter, nor am I ignorant that it is 
requisite to distinguish and estimate even the influence of hori- 
zontal distances, or of climates, upon the specific differences; 
that we must know to appreciate the apparent, sometimes even 
real, points of resemblance, which present themselves in forma- 
tions which are evidently very distinct, in certain species which 
have had the rather rare privilege of surviving the destruction 
of their cotemporaries; and of remaining always the same, in the 
midst of all the changes which have taken place around them. 
I am not ignorant that we must know to recognise the indivi- 
duals wrested from other deposits, and transported, by whatever 
causes, to newer ones, and to distinguish them from those which 
have lived in the places and times, which the species, to which 
they belong, ought to characterise. I am aware of all these dif- 
ficulties ; I am on my guard against these causes of deception, 
which introduce uncertainties into geology, such as we meet in 
all the sciences, and which require of the geologist unremitting 
attention and labour, to employ with discernment the species 
from which he must take his characters, and to attach to them 
fthc true value which in reality belongs to them. 
