Page:The American Cyclopædia (1879) Volume VII.djvu/709

Rh constituting the Erie division of the New York series, the equivalent of the English Devonian or old red sandstone, and characterized by an abundant terrestrial fauna, the precursor of that of the carboniferous series, into which it passes by such transitions that it is a matter of discussion where to draw the line. The carboniferous series is so named because it is the earliest and most important coal-bearing series of strata, and includes great beds of fossil fuel, interstratified with sandstones and shales. At the base of the carboniferous in Michigan, Pennsylvania, and western Virginia, and also in Nova Scotia and New Brunswick, deposits of gypsum and salt are met with. In the western part of its distribution, toward the Mississippi, the carboniferous formation includes great thicknesses of marine limestone, which are wanting in the east. Overlying the carboniferous in Kansas and Iowa are beds which are the equivalent of the magnesian limestones of the north of England, and of the rocks called Permian in Russia. They are regarded as the summit of the palæozoic series.—The palæozoic rocks correspond to the transition rocks of Werner, to the lower part of which the name of the graywacke series was very generally given until the labors of Sedgwick and Murchison classified them and established the great divisions of Cambrian, Silurian, and Devonian. The thickness of these groups varies greatly in different parts of their distribution. Thus, while the entire palæozoic series in Pennsylvania is estimated at 40,000 ft., it is reduced to 4,000 in the valley of the Mississippi. This is due to the fact that the great sandstones, apparently derived from the erosion of rocks to the eastward, thin out in the opposite direction. In a similar manner the Cambrian and Silurian rocks, which attain in Great Britain a thickness of 30,000 ft., are represented by less than 2,000 ft. in Scandinavia.—Under the name of mesozoic or secondary rocks are included the triassic, Jurassic, and cretaceous series. The former has received its name from the threefold division of it in Europe into sandstones, overlaid by fossiliferous limestones, which are succeeded by sandstones and shales. At the base of the trias in the Tyrol, at St. Cassian and Haltstadt, occurs a series of fossiliferous beds in which the characteristic animal remains of the trias are found mingled with those of the palæozoic, thus showing a passage between the palæozoic and the mesozoic rocks. The trias, both in England and on the continent of Europe, is characterized by beds of rock salt and gypsum, like the Silurian and the lower carboniferous in North America. The sandstones of the trias in England are often red, and constitute what is there named the new red sandstone. The same name is applied to sandstones of similar age which are found in Prince Edward island and Nova Scotia, in the valley of the Connecticut, and in New Jersey, Pennsylvania, Virginia, and North Carolina. To this series belong the coal fields of Richmond, Va., and Chatham, N. C. It is not improbable that these beds may include strata belonging to the subsequent or Jurassic period, so named because it is greatly developed in the Jura mountains. This includes both the lias and the oölite of England, which two on the continent are connected by beds of passage known as the Koessen or Rhætic strata. The oölite of England consists of highly fossilfferous strata, chiefly marine, but in part fresh-water deposits, and through the Neocomian (Neufchâtel) beds passes into the cretaceous or chalk formation, the upper part of which is characterized in northern Europe by that pure uncrystalline limestone known as the chalk, a deep-sea deposit many hundred feet in thickness, made up almost entirely of the remains of minute animal organisms.—The rocks of the cenozoic or tertiary period are closely connected with the present time, and even in their lower portions contain some species of fossil shells identical with those now living. Lyell has conveniently divided the tertiary, in ascending order, into eocene, miocene, and pliocene; to these are added a postpliocene division which includes the period of glacial drift. (See .) The tertiary rocks attained a great thickness in some parts of their distribution. Thus in the Alps the miocene sandstones and conglomerates, known as the molasse, have in parts a thickness of more than 6,000 ft., while the nummulitic limestone, a subdivision belonging to the base of the tertiary, attains in the Mediterranean basin a thickness of more than 2,000 ft.—We have already spoken of the trias of the eastern part of North America. The cretaceous is also represented in New Jersey and along the southern border of the palæozoic from Georgia to Tennessee. Triassic, Jurassic, and cretaceous rocks are also widely spread between the Mississippi and the Rocky mountains, from Texas to Dakota, and westward over large areas to the Pacific coast. Deposits like the English chalk are unknown in this formation in North America. Tertiary rocks of various ages skirt the Atlantic coast from the Rio Grande to New Jersey, and are even met with off the coast of Massachusetts. They stretch from the gulf of Mexico to Kentucky, and like the mesozoic rocks occupy large areas to the westward, where on the Pacific coast they attain great thickness.—The succession of organic life in these various groups constitutes a study by itself, which will be considered under the head of. The palæozoic age is preeminently the period of mollusks, corals, and crustaceans, the most important class of which last in the early times were the trilobites, which appear in their greatest development in the Cambrian and Silurian, and die out in the carboniferous. Fishes, the earliest representatives of vertebrate life, make their appearance near the summit of the Silurian, and abound in the upper palæozoic; reptiles first appear in the carboniferous, and reach their greatest development in the mesozoic, in which