subsequent perturbations of this region, and that these Cretaceous
deposits, after they had become consolidated, were raised by later
upheavals from their original position to that which they now occupy on
the lower slope of the Jura, resting immediately, but in geological
language _unconformably_, against it. The two adjoining wood-cuts are
merely theoretical, showing by lines the past and the present relation of
these deposits; but they may assist the reader to understand my meaning.

[Illustration]

Figure 1 represents the Jura before the Alps were raised, with the
Cretaceous deposits accumulating beneath the sea at its base. The line
marked S indicates the ocean-level; the letter c, the Cretaceous deposits;
the letter j, the Jurassic strata, lifted on the side of the mountain.

[Illustration]

Figure 2 represents the Jura at the present time, when the later upheavals
have lifted the Jurassic strata to a sharper inclination with the
Cretaceous deposits, now raised and forming the lower slope of the
mountain, at the base of which is the Lake of Neufchatel.

Although this change of inclination is hardly perceptible, as one looks up
against the face of the Jura range, there is a transverse cut across it
which seems intended to give us a diagram of its internal structure.
Behind the city of Neufchatel rises the mountain of Chaumont, so called
from its bald head, for neither tree nor shrub grows on its summit.
Straight through this mountain, from its northern to its southern side,
there is a natural road, formed by a split in the mountain from top to
bottom. In this transverse cut, which forms one of the most romantic and
picturesque gorges leading into the heart of the Jura range, you get a
profile view of the change in the inclination of the strata, and can
easily distinguish the point of juncture between the two sets of deposits.
But even after this dislocation of strata had been perceived, it was not
known that it indicated the commencement of a new epoch, and it is here
that my own share in the work, such as it is, belongs. Accustomed as a boy
to ramble about in the beautiful gorges and valleys of the Jura, and in
riper years, as my interest in science increased, to study its formation
with closer attention, this difference in the inclination of the slope had
not escaped my observation. I was, however, still more attracted by the
fossils it contained than by its geological character: and, indeed, there
is no bett