[9] Geological Researches, p. 334.

[10] Buckland, Bridgewater Treatise, p. 307.

[11] A History of Fossil Insects, etc., 1846. London.

[12] Tableau des Vég. Foss., 1849, p. 105.

[13] Conybeare and Philips’s Outlines, etc., p. 166.

[14] Geological Researches, p. 337.

CHAPTER XXI.
TRIAS, OR NEW RED SANDSTONE GROUP.

Beds of Passage between the Lias and Trias, Rhætic Beds. — Triassic Mammifer. — Triple Division of the Trias. — Keuper, or Upper Trias of England. — Reptiles of the Upper Trias. — Foot-prints in the Bunter formation in England. — Dolomitic Conglomerate of Bristol. — Origin of Red Sandstone and Rock-salt. — Precipitation of Salt from inland Lakes and Lagoons. — Trias of Germany. — Keuper. — St. Cassian and Hallstadt Beds. — Peculiarity of their Fauna. — Muschelkalk and its Fossils. — Trias of the United States. — Fossil Foot-prints of Birds and Reptiles in the Valley of the Connecticut. — Triassic Mammifer of North Carolina. — Triassic Coal-field of Richmond, Virginia. — Low Grade of early Mammals favourable to the Theory of Progressive Development.

Beds of Passage between the Lias and Trias—Rhætic Beds.—We have mentioned in the last chapter ([p. 356]) that the base of the Lower Lias is characterised, both in England and Germany, by beds containing distinct species of Ammonites, the lowest subdivision having been called the zone of Ammonites planorbis. Below this zone, on the boundary line between the Lias and the strata of which we are about to treat, called “Trias,” certain cream-coloured limestones devoid of fossils are usually found. These white beds were called by William Smith the White Lias, and they have been shown by Mr. Charles Moore to belong to a formation similar to one in the Rhætian Alps of Bavaria, to which Mr. Gumbel has applied the name of Rhætic. They have also long been known as the Koessen beds in Germany, and may be regarded as beds of passage between the Lias and Trias. They are named the Penarth beds by the Government surveyors of Great Britain, from Penarth, near Cardiff, in Glamorganshire, where they sometimes attain a thickness of fifty feet.

The principal member of this group has been called by Dr. Wright the Avicula contorta bed,[[1]] as this shell is very abundant, and has a wide range in Europe. General Portlock first described the formation as it occurs at Portrush, in Antrim, where the Avicula contorta is accompanied by Pecten Valoniensis, as in Germany.