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.
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