Ch. XX.] 
ENGLISH EOCENE FORMATIONS. 
277 
of the insects have been supposed identical with species now 
living*. These insects have been almost exclusively procured 
from a thin bed of grey calcareous marl, which passes into an 
argillaceous limestone found in the quarries of gypsum near 
.Aix. The rock in which they are imbedded is so thinly lami- 
nated that there are sometimes more than 70 layers in the 
thickness of an inch. The insects are for the most part in 
an extraordinary state of preservation, and an impression of 
their form is seen both on the upper and under laminse, as in the 
case of the Monte Bolca fishes. M. Marcel de Serres enume- 
rates 62 genera belonging chiefiy to the orders Diptera, 
Hemiptera and Coleoptera. On reviewing a collection brought 
from Aix, Mr. Curtis observes that they are all of European 
forms and most of them referrible to existing genera f . With 
the single exception of an Hydrobius, none of the species are 
aquatic. The antennas, tarsi, and trophi are generally very 
obscure, or distorted, yet in a few the claws are visible, and the 
sculpture, and even some degree of local colouring, are pre- 
served. The nerves of the wings, in almost all the Diptera, 
are perfectly distinct, and even the pubescence on the head of 
one of them. Several of the beetles have the wings extended 
beyond the elytra, as if they had made an effort to escape by 
flying, or had fallen into the water while on the wing 
BASINS OF LONDON AND HAMPSHIRE. 
The reader will see in the small map above given (No. 62, 
p. 275,) the position of the two districts usually called the 
basins of London and Hampshire, to which the Eocene for- 
mations of England are confined. These tracts are bounded 
by rising grounds composed of chalk, except where the sea 
intervenes. That the chalk passes beneath tiie tertiary strata, 
we can not only infer from geological data, but can prove by 
numerous artificial sections at points where wells have been 
sunk, or borings made through the overlying beds. The 
* M. Marcel de Serres, Geog. des Ter. Tertiaires du Midi de la France, 
t Murchison and Lyell. Ed. New Phil. Journ., Oct. 1829. 
% Curtis, ibid., where figures of some of the insects are given. 
