its
characteristic fossils may be readily obtained; this formation here also
frequently contains its usual layers of flint, and which often assumes
the exact form of the zoophytes, and other organic structures, into
which it has percolated.

But in this locality, as also in many instances in the chalk region
south of Angouleme, the mineralogical character of the formation is
often completely altered, chiefly appearing as a fine white calcareous
sandstone, occasionally passing into a compact siliceous limestone,
similar to the _calcaire siliceux_ of the superior freshwater limestone,
but for the most part destitute of the small sinuous cavities the
latter commonly contains.

This calcareous sandstone is directly succeeded, in ascending order, by
the most extensive surface deposit of Touraine, termed by the French
geologist, argile et poudinge; a rather thick argillaceous deposit, in
which flint boulders are sometimes thickly embedded, and on which
reposes the _calc d'eau douce_ or freshwater limestone, both formations
belonging to the uppermost subdivision of the Parisian tertiary strata,
or newer Pliocene deposits.

Immediately above the freshwater limestone just named, a series of
isolated masses occur, consisting of marine sand and marl, the whole
rarely exceeding fifty feet in thickness, and containing for the most
part a different and immense assemblage of fossils. This tertiary
formation which is provincially termed _faluns_, (broken shells) is
considered to belong to a period intermediate between that of the
Parisian and subapennine strata, and to assimulate in age to the crag
formation of England, which belongs to the Miocene or middle Tertiary.

Mr Lyell who has closely examined the _faluns_[D], says that most of
the shells they contain do not depart from the Mediterranean type,
although a few would seem to indicate a tropical climate, among these
may be mentioned some large species of the genera _conus_, _terebra_,
_rynula_, _tasciolaria_, _cerithium_ and _cardita_.

The species he considers for the most part marine, but that a few of
them belong to land and fluviatile genera. Among the former, _helix
turonensis_ (faluns Touraine) is the most abundant.

Remains of terrestrial quadrupeds are here and there intermixed,
belonging to the genera mastodon, rhinoceros, hyppopotamus, deer and
others, and these are accompanied by cetacea, such as the lamantine,
morse, sea calf, and dolphin, all of extinct species