Scientific Reviews. 119 
and are applied toa different nature of deposits, and to formations 
of dissimilar ages. 
It is certain that De Humboldt, in applying his knowledge of 
European formations to the structure of the Andes, found himself 
at a loss, and expressly states the entire uselessness of what he 
terms oryetognostic characters in recognizing the age of a mountain 
rock. But it is equally certain that errors have sprung from an in- 
attention to these facts, or whence should we trace the necessity of 
Mr. De la Beche’s excellent paper on the differences in structure 
which are observable in secondary stratified rocks ? 
How constant it is to find the characters of a mountain given in 
our elementary works as certain, when, in the present state of the 
science, we should only be engaged in studying its varieties ; or, if 
we must teach before we know, we should be occupied in detailing 
the various appearances which the same formations may assume in 
different countries ; for we know that a formation represented by 
an oolitic structure in one country, may become a compact lime- 
stone in another,—that the blue clay by geognosts termed lias, may 
become a compact hard dark limestone, and, if Von Buch is right, 
may be penetrated through with pyroxene or augite ! 
The detection and study of the organic remains, buried in the 
formations which constitute the crust of the globe, while they gave 
a new character to geognostic research, and led to the develope- 
ment of some most striking truths, from being pursued with too 
much enthusiasm, and from placing too unbounded a reliance on 
their constancy, have led to grave errors in facts. 
We do not find that exactly the same shells characterize the supe- 
rior order of formations of England and France, or the supermedial 
formations of the north and of the south of France ; and the more 
modern the rock, as might be expected from the difference of cli- 
mate, the greater do we perceive the difference in organic remains. 
The higher animals, met with in certain beds of the superior for- 
mation, have now been found more extensively dispersed. They 
must have lived in countries where successive catastrophes took 
place. Thus, animals resided by the banks of a great lake in Au- 
vergne, before. its volcanoes had burst forth, and the Paleotherium 
wandered on the banks of the ancient sea or lake of Lutetia, from 
the deposition of the oldest to the occurrence of almost the newest 
beds which now occupy the situation of former waters. 
The tropical animals, found in the company of ruminants and 
carnivorous animals of the north, have been found wandering from 
their supposed cavernous haunts to the blue marls of Yorkshire ; 
and amidst the numerous and beautiful facts which industry is 
daily pouring into the clear stream of geognostical science, we find 
the source of a new certainty, which will flow to that science, as 
surely as truth will ever be found by those who worship her for 
herself. 
Positive geognosy, in contradistinction to geology, used by De 
Humboldt as historical, is a science which consists in the constant 
