Part IIL. Seor.i.§2.] TRIASSIC. 765 
materials, contain abundant rolled pebbles of quartz which have 
evidently been derived from some previous conglomerate, probably from 
some of the Old Red Sandstone masses now removed or concealed. The 
Trias rests with a more or less decided unconformability on the rocks 
underneath it, so that, although the general physical conditions as re- 
gards climate, geography, and sedimentation, which prevailed in the 
Permian period still continued, terrestrial movements had, in the mean- 
while, taken place, whereby the Permian sediments were generally up- 
raised and exposed to denudation. Hence the Trias rests now on 
Permian, now on Carboniferous, and sometimes even on Cambrian rocks. 
Moreover, the upper parts of the Triassic series overlap the lower, so 
that the Keuper groups repose successively on Permian and Carboniferous 
rocks. 
The beds of rock-salt in the English Trias have long been profitably 
worked. The uppermost subdivision of the Keuper, consisting of red 
marls, has a wide distribution, for it can be traced from the coast of 
Lancashire to the Bristol Channel, and covers a larger area of surface in 
the central counties than the rest of the Trias and the whole of the 
Permian sandstones combined. LEvenas far south as the coast of Devon- 
shire, it contains casts of the cubical spaces once occupied by crystals of 
- common salt. But in Cheshire the salt occurs in two or more beds, of 
which the lower is sometimes upwards of 100 feet thick. It is a- 
crystalline substance, usually tinged yellow or red from intermixture of 
clay and peroxide of iron, but is tolerably pure in the best parts of the 
beds, where the proportion of chloride of sodium is as much as 98 per 
cent. Through the bright red marls with which the salt is interstrati- 
fied there run bands of gypsum, somewhat irregular in their mode of 
occurrence, sometimes reaching a thickness of 40 feet and upwards. ‘Thin 
seams of rock-salt likewise occur among the red mars. 
As compared with the Trias of Germany and France the most dis- 
tinctive feature of the English development of the system is the absence 
_ of the central calcareous and dolomitic member. 1t will be observed, 
_ Indeed, from the foregoing table that a zone of calcareous conglomerate 
or breccia is frequently observable in central England at the base of the 
Keuper groups. Inthe Bristol area a remarkable dolomitic conglomerate, 
marking a shore line in Triassic times, occupies perhaps the same position. 
lt averages 20 feet in thickness, but rises here and there into cliffs 40 or 
50 feet high. It has yielded two genera of Deinosaurs, Palzosaurus and 
Thecodontosaurus.1 (See pp. 486, 493.) 
The organic remains of the English Bunter and Keuper are com- 
paratively few, as the conditions for at least animal life must have been 
extremely unfavourable in the waters of the ancient Dead Sea wherein 
these red rocks were accumulated. ‘The land possessed a vegetation 
which, from the fragments yet known, seems to have consisted in large 
measure of cypress-like coniferous trees ( Volizia, Walchia), with calamites 
on the lower more marshy grounds. The red marl group contains in 
some of its layers numerous valves of the little crustacean Estheria 
minuta, and a solitary species of lamellibranch, Pullastra arenicola. A 
number of teeth, spines, and sometimes entire skeletons of fish have 
been obtained (Dipteronotus cyphus, Palzeoniscus superstes, Hybodus Keuperi, 
Acrodus minimus, Sphenonchus minimus, Lophodus, &c.). The bones, and 
1 Etheridge, Q. J. Geol. Soc. xxvi. 174. 
