I. The lowest division of the Trias is known as the _Bunter Sandstein_ (the _Grès bigarré_ of the French), from the generally variegated colours of the beds which compose it (German, _bunt_, variegated). The Bunter Sandstein of the continent of Europe consists of red and white sandstones, with red clays, 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 unconsolidated 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 _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 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 Rhætic beds (from the Rhætic 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 Kössen 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_).