^4 Baron A. Humboldt on Petrifactions, or 
and its marls, the ananchytes and spatangi to the chalk, the cerx- 
thia to the coarse limestone ; the knowledge of these genera 
would prove an easy and effectual aid in the determination of 
rocks : it would no longer be requisite to examine the super- 
position of formations on the spot, for they could be distiu - 
guished without stirring from one’s cabinet, by the mere exami- 
nation of specimens. But it is far from being the case that na- 
ture has rendered the study of the shelly masses which compose 
the crust of the earth so easy to man. The same types of orga- 
nization are repeated at very different epochs. The same 
genera occur in different formations. There are orthoeeratites 
in the transition - limestones, the Alpine limestones, and the 
variegated sandstone; terebratulites in the Jura limestone and 
shell-limestone (muschelkalk) ; trilobites in the transition clay- 
slates (thonschiefer), in the bituminous marl-slate, and, ac- 
cording to an excellent geognost, M. de Schlottheim, even 
in the Jura limestone. There are pentacrinites in the transi- 
tion clay-slate and the newest shell-limestone (muschelkalk). 
The ammonites penetrate across many of the limestone and 
marl formations, from the greywackes to the lower beds of the 
chalk. Trunks of monocotyledonous plants are found both in 
the red sandstone and in the marls of the fresh- water gypsum, 
formed at a period when the world was already filled with mo- 
nocotyledonous vegetables. 
But at a period when naturalists are no longer satisfied with 
vague and uncertain notions, it has been discovered that the 
greater number of those petrifactions or fossils (gryphites, tere- 
bratulites, ammonites, trilobites, &c.) imbedded in different for- 
mations, are not specifically the same ; and that a great number 
of species which have been determined with precision, vary with 
the superimposed rocks. The fishes which are observed in the 
transition-slates (Glaris), in the zechstein or bituminous marl- 
slate, in the Jura limestone, in the tertiary limestone with ceri- 
thia of Paris and Monte Bolca, and in the gypsum of Mont- 
martre, are distinct species, partly pelagic and partly fluviatile. 
Might it be concluded, from these facts, that all the formations 
are characterised by particular species ; that the fossil-shells of 
the chalk, of the shell-limestone (muschelkalk), of the Jura 
limestone, and of the alpine limestone, are all different from 
