Marnes irisees_ of the
French), as it is generally called, occurs in England; but is
not so well developed as it is in Germany. In Britain, the Keuper
is 1000 feet or more in thickness, and consists of white and
brown sandstones, with red marls, the whole topped by red clays
with rock-salt and gypsum.

The Keuper in Britain is extremely unfossiliferous; but it passes
upwards with perfect conformity into a very remarkable group of
beds, at one time classed with the Lias, and now known under the
names of the Penarth beds (from Penarth, in Glamorganshire), the
Rhaetic beds (from the Rhaetic Alps), or the _Avicula contorta_ beds
(from the occurrence in them of great numbers of this peculiar
Bivalve). These singular beds have been variously regarded as the
highest beds of the Trias, or the lowest beds of the Lias, or as
an intermediate group. The phenomena observed on the Continent,
however, render it best to consider them as Triassic, as they
certainly agree with the so-called Upper St Cassian or Koessen
beds which form the top of the Trias in the Austrian Alps.

The Penarth beds occur in Glamorganshire, Gloucestershire,
Warwickshire, Staffordshire, and the north of Ireland; and they
generally consist of a small thickness of grey marls, white
limestones, and black shales, surmounted conformably by the lowest
beds of the Lias. The most characteristic fossils which they contain
are the three Bivalves _Cardium Rhoeticum, Avicula contorta_, and
_Pecten Valoniensis_; but they have yielded many other fossils,
amongst which the most important are the remains of Fishes and
small Mammals (_Microlestes_).

In the Austrian Alps the Trias terminates upwards in an extraordinary
series of fossiliferous beds, replete with marine fossils. Sir
Charles Lyell gives the following table of these remarkable
deposits:--

_Strata below the Lias in the Austrian Alps, in descending order._

/ Grey and black limestone, with calcareous
| marls having a thickness of about 50
| feet. Among the fossils, Brachiopoda
1. Koessen beds. | very numerous; some few species common
(Synonyms, Upper | to the genuine Lias; many peculiar.
St Cassian beds of < _Avicula contorta, Pecten Valoniensis_,
Escher and Merian.) | _Cardium Rhoeticum, Avicula_
| _inoequivalvis, Spirifer Muensteri_,
| Dav. Strata containin