The existence of the great Mediterranean Thetys in part of the Triassic period is indicated by the oceanic deposits which occur in Asia Minor, Central Asia, Baluchistan, Afghanistan, northern India, and Burmah, Tongking, and Southern China, but in the Lower Trias it appears that India was not in connection with Europe. In the Salt Range of northwestern India and the Himalayas is a remarkably complete succession of Triassic rocks, which overlie the Permian in a conformity that is at least apparent and may be actual, though there is a faunal break between the two systems. The Brahmanian stage of India is not represented in the Alps. In central India the Gondwana conditions of continental sedimentation continued apparently through the whole Triassic. Rocks of this period, which seem to belong in another faunal province, occur in Japan, the east coast of Siberia, and the Arctic islands, Spitzbergen, and Bear Island.
In the early part, at least, of the period, both North and South America extended farther east than at present, and no marine Triassic rocks are known on the Atlantic slope of either continent, but they are extensively displayed on the Pacific side. The land barrier which during the Palaeozoic era had bounded the Great Basin sea on the west was submerged and the Pacific extended over the site of the Sierras, covering western Nevada and sending a gulf into southeastern Idaho, and in British Columbia it transgressed eastward across the present mountains, and it covered part of the coast of Alaska. In California and Nevada all the series and many of the stages of the oceanic Trias may be identified and their faunal relations change in a very interesting way. The lower series (Scythic) "shows an intimate relationship to that of Asia and none with that of the Mediterranean region" (J. P. Smith), and this relationship is both with India and northern Asia. The difference from Europe is no doubt to be explained by the fact, above referred to, that in the Lower Trias, Thetys was interrupted somewhere between India and Europe. In the Di-naric series an invasion from the Mediterranean region is evident, though the track followed by this migration is not clear.
In the Upper Trias (Tirolic series) the relations were first with India and the Mediterranean, succeeded by another migration from the north of Asia. These changes in faunal relationships have been variously explained and will again be referred to in considering the question of theTriassic climates. Little of the Bajuvaric series is found on the Pacific coast. In the United States the. marine Triassic rocks do not exceed 4800 feet in maximum thickness, but in British Columbia this increases to 13,000, much of which is igneous material, and similar material is widely distributed in southeastern Alaska.
Fig. 282. - Map of North America in the Triassic and Jurassic periods. Black areas = known exposures; white areas = land ; lined areas= sea; dotted areas = continental deposits. The horizontal lines indicate Triassic, and the vertical lines Jurassic, seas.
In central Mexico, State of Zacatecas, is an isolated area of marine Trias, belonging to the Tirolic series of the Upper Triassic and with a fauna allied to that of California. This is probably only a remnant of a formerly widespread area of such rocks, nearly all of which were eroded away during the Lower and Middle Jurassic, when most of Mexico was land.
On the Atlantic side of North America the course of events was entirely different. In the latter half of the period was formed a series of long, narrow troughs, running closely parallel to the trend of the Appalachian Mountains, but separated from them by the ridges of metamorphic and crystalline rocks, which follow those mountains on the east, and which then probably had a considerable altitude, much greater than at present. In these troughs was laid down the enormous thickness of non-marine rocks which constitute the Newark series and are now found in several disconnected areas from Nova Scotia to North Carolina. The longest continuous stretch of these beds is from the Hudson River across New Jersey, southeastern Pennsylvania and Maryland, into Virginia, while another extensive area occupies the Connecticut valley, through western Connecticut and Massachusetts. The Newark areas have been so extensively faulted that it is difficult to ascertain their thickness, and the figures given are merely an approximation.
The series reaches its maximum in southeastern Pennsylvania, where it is estimated at 20,000 feet, in New Jersey 12,000-15,000, and in the Connecticut valley, 13,000. Southward the rocks thin quite rapidly, and about Richmond, Va., are not more than 3000 feet thick, and farther south, still less.
The Newark rocks are prevailingly red sandstones and shales, especially from Pennsylvania northward, but also contain some very coarse conglomerates at the base, and higher up in the series along the western border of the area. Thin bands of limestone and black, fossiliferous shales are intercalated, and in New Jersey is a thick mass of very hard, slate-coloured shales, the Lockatong stage. In the northern area, Connecticut valley, New Jersey, and Pennsylvania, many of the beds are ripple-marked, sun-cracked, pitted with raindrops, and preserve countless footprints of Amphibia and land Reptiles. In Virginia and North Carolina are workable coal-seams, and the red colour of the other rocks is less prevalent than in the North. Except in the black shales, fossils are very few, and the plants show a distinct difference between the Virginia and North Carolina area, where ferns predominate, and the New Jersey-Connecticut region, where ferns are less abundant and gymnosperms more so. Whether this difference is climatic or due to a slight difference in geological date it is difficult to say.