204 HISTORICAL PALAZZONTOLOGY. 
and thin limestones, the whole attaining a thickness of about 
1500 feet. The term “marl” is very generally employed to 
designate the clays of the Lower and Upper Trias; but the 
term is inappropriate, as they may contain no lime, and are 
therefore not always genuine marls. In Britain the Bunter 
Sandstein consists of red and mottled sandstones, with uncon- 
solidated conglomerates, or ‘ pebble-beds,” the whole having 
a thickness of 1000 to 2000 feet. ‘The Bunter Sandstein, as 
a rule, is very barren of fossils. 
II. The Middle Trias is not developed in Bnitain, but it 
is largely developed in Germany, where it constitutes what is 
known as the AZuschelkalk (Germ. AZuschel, mussel ; kalk, lime- 
stone), from the abundance of fossil shells which it contains. 
The Muschelkalk (the Calcatre cogut/lier 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 A/arnes irisées 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 Rhezetic beds (from the Rheetic 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 Kossen 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 Rheticum, Avicula 
contorta, and Pecten Valoniensis ; but they have yielded many 
other fossils, amongst which the most important are the re- 
mains of Fishes and small Mammals (A@icrolestes). 
In the Austrian Alps the Trias terminates upwards in an 
