28 Baron A. Humboldt on Petrifactions, or 
formed, the beings which then inhabited the surface of the globe 
were all destroyed ? 
It is incontestible, that generations of different types have 
succeeded one another. The ammonites, which scarcely occur 
among the transition rocks, attain their maximum in the strata 
which on different points of the globe represent the shell-lime- 
stone (muschelkalk) and Jura limestone ; they disappear in the 
upper beds of the chalk, and above this formation. The echi- 
nites, which are very rare in the alpine limestone, and even in 
the shell-limestone (muschelkalk), become, on the contrary, very 
common in the Jura limestone, in the chalk and the tertiary 
formations. But nothing proves to us that this succession of 
different organic types, this gradual destruction of genera and 
of species, necessarily coincides with the periods when each for- 
mation was deposited. 66 The consideration of similarity, or of 
discrepancy between organic remains, is not of great import- 
ance,” says M. Beudant ( Voyages Min. v. iii. p. 278.), “ when 
we compare deposits formed in countries very remote from each 
other ; but it is of much importance, when we compare those 
which are very near.” 
In combating the two absolute conclusions which might be 
attempted to be derived from the validity of zoological charac- 
ters, I am far from denying the important services which the 
study of fossil bodies renders to geognosy, if we consider this 
science under a philosophical point of view. Geognosy does not 
limit itself to the searching for diagnostical characters ; it em- 
braces the aggregate of relations under which each formation 
may be considered: 1st, Its relative position; Qdly, Its oryc- 
tognostic constitution (that is to say, its chemical composition, 
and the particular mode of aggregation, more or less crystalline, 
of its molecules) ; 8 dly, The association of different organic bo- 
dies which occur imbedded in it. If the superposition of hete- 
rogeneous rocky masses reveals to us the successive order of 
their formation, is it not also interesting to know the state of or- 
ganic nature at the different periods when these deposits were 
formed ? Can it be questioned, that, over a surface of many 
thousands of square leagues (in Thuringia, and in all the north- 
ern part of Germany), nine superimposed formations, those, 
namely, of the transition limestone, greywacke, red sandstone, 
