658 
caution have been bestowed than he gave to the consideration of the 
names for the subdivision of the Tertiary Series, as founded on a 
great philosophical view. Whatever objections some persons might 
entertain to the upper divisions of his system, the characters of which 
were made to depend on a greater or less per-centage of existing 
species, there could be little doubt, from the multitude of previous 
researches, that his term “Eocene” was at all events secure from 
criticism. Many practical geologists believed that the close of the 
Secondary period was marked by some great agent of change, which 
in modifying the surface was followed by the creation of new races 
of animals. A few only argued that such a disruption or break 
in the sequence of organic life must be a partial phenomenon, and 
that as observations extended, we should find parts of the earth, 
where transition strata of the supra-cretaceous age would fill up the 
hiatus which seemed apparent between the chalk and the tertiary 
strata over wide tracts of Europe. Such transitions, for example, it 
was contended, were observed by Professor Sedgwick and myself 
in the Austrian Alps, but the justness of our views was then combat- 
ed by Boué, a geologist of great experience and research, whilst M. 
de Beaumont, M. d’Orbigny, and M. Michelin have since decided 
against us, the first mentioned by a visit to the spot, the two others 
by analogies worked out in the South of France. If our adversaries 
should prove correct, the microscope of Ehrenberg has done more 
than the eyes of the geologist ; for whilst in the case of Gosau* the 
number of tertiary-like genera, such as Volutes, Cerithia, Mitra, 
&c., and the absence of all Ammonites and Belemnites constituted - 
our case, the discovery of the Prussian microscopist goes to prove, 
from specific forms, that the Eocene or dawn of the present fauna 
had its germ in rocks as old as our chalk; and thus if we should be 
led to adopt his views, which however we can only do after some 
time and with great caution, the only barrier line which was abruptly 
placed between two formations as a general phenomenon, would be 
shaded off so as imperceptibly to connect the Secondary and Tertiary 
states of organic life. 
In our own country this department of the science, which is in 
* In regard to Gosau I must in candour state, that M. d’Orbigny has 
discovered in the upper greensand, ‘‘Craie chloritée,” at Uchaux near 
Vaucluse, thirty-one species of Ammonites associated with some of the 
same species of Corais and Univalves, which occur at Gosau, and M. Mi- 
chelin had indeed previously discovered other Gosau forms of corallines 
supposed to be of the age of the “ gault”’ deposits, and thus no doubt seems 
to. remain that the myriads of ¢ertiary-like shells, and the absence of Am- 
monites and Belemnites on which Professor Sedgwick and myself rested 
our chief conclusions, cannot be assumed as proofs of the age of the Gosau 
rocks. It still, howeyer, remains to be ascertained, whether this peculiar 
development of the cretaceous system of the Alps (in which one Am- 
monite only has been discovered and no Belemnite) is not after all a link 
between what has been called Tertiary and Secondary. At all events, the 
nea on the flanks of the Alps at Kressenberg, &c. lead to this con- 
clusion. 
