32 Baron A.. Humboldt on Petrifactions , or 
members more or less developed of the same formation, (Freies- 
leben, Kupf v. i. p. 17. v. iii. p. 1). 
Notwithstanding the mixture of pelagic and fluviatile shells 
which is sometimes observed at the point of contact of two forma- 
tions of different origin, the name of Marine Limestone , or of 
Marine Sandstone , may be given to the one of these formations, 
when the denomination of the rocks could only be taken from the 
species which constitute the greatest mass and the centre of the 
beds. This terminology recalls a fact which bears relation, so to 
speak, to geogony, to the ancient history of our planet : it fixes 
(and perhaps a little too much) the alternation of the fresh and of 
the salt waters. I do not dispute the utility of the denominations 
marine limestone , or marine sandstone , with regard tolocal descrip- 
tions ; but, according to the principles which I have proposed to 
follow, in the general classification of formations, characterized, 
according to the place which they occupy, as terms of a series, I 
have deemed it necessary to avoid them with care. Are all the 
formations beneath the chalk, or even beneath the limestone, 
with cerithia (coarse limestone of the basin of Paris), without ex- 
ception, marine limestones and sandstones ? or do the monitors 
and fishes of the bituminous copper-slate in the alpine limestone 
of Thuringia ; the ichthyosauri of Mr Hgme, placed beneath the 
Oxford and Bath oolites, in the lias of England, (which, on the 
Continent, is represented by a part of the Jura limestone) ; the 
crocodiles of Honfieur, contained in clays, with limestone-beds 
above the oolites of Dive and Isigny limestone, and consequent- 
ly superior to the Jura limestone, — do all these prove, that there 
are already beneath the chalk, between that formation and thered 
sandstone, small fresh-water formations superadded to the great 
marine formations ? Do not the. coals containing ferns, situated 
beneath the red-sandstone and beneath the secondary porphyry, 
present an evident example of a very ancient formation, not of 
marine origin ? These circumstances show the necessity of much 
caution in the present state of science, when, from characters 
purely zoological, it is attempted to divide formations, whose uni- 
ty has appeared confirmed by the alternation of the same beds, 
and by other phenomena of relative position. (Engelhard und 
Baumer, Geogn. Vers. p. 125.-133.) This caution is so much 
the more necessary, that, according to the testimony of a mine- 
1 
