II.  The Middle Trias is not developed in Britain, but it is largely developed in Germany, where it constitutes what is known as the Muschelkalk (Germ. Muschel, mussel; kalk, limestone), from the abundance of fossil shells which it contains.  The Muschelkalk (the Calcaire coquillier of the French) consists of compact grey or yellowish limestones, sometimes dolomitic, and including occasional beds of gypsum and rock-salt.

III.  The Upper Trias, or Keuper (the 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 containing the above fossils
| alternate with the Dachstein beds, lying