204 HISTORICAL PALAEONTOLOGY. 



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 Britain, but it 

 is largely developed in Germany, where it constitutes what is 

 known as the Mnschelkalk (Germ. Muschel, mussel ; kalk, lime- 

 stone), 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 Keupcr (the JMarnes 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 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 Rhcetiaim, 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 (Microlestes). 



In the Austrian Alps the Trias terminates upwards in en 



