DEVONIAN FORMATION, DEVONIAN SYSTEM (ante). At the beginning of the Devonian period the dry land of North America was confined to the present territory of eastern Canada and New England. The Alleghany mountains were sketched in a series of islands and coral reefs which made a barrier between the ocean and the inland sea. There were no large rivers; the valleys of the Hudson, the Connecticut, and the St. Lawrence were merely outlined, and the Ottawa had begun its work in the azoic region between the St. Lawrence and Labrador. The Devonian period was occupied by a series of oscillations of level, the amplitude of the variations, and the consequent thicknesses of deposit being greater in the eastern part. The mediterranean of the interior opened R. into the gulf of Mexico, n. into the Arctic sea, and covered all the northern central region of the present continent with shallow lagoons, separated by low sandy areas.
According to the geologists of the New York survey, the D. F. of America is arranged thus, beginning at the top: 1. The Oriskany sandstone extends from near Oriskany, Oneida co., N. Y., s.w. along the Appalachians into Pennsylvania, Maryland, and Virginia. It appears near Buffalo, in Canada near Waterloo, in Ohio, Indiana, southern Illinois, and Missouri. Its thickness at Oriskany is about 30 ft.; in Illinois, 250 to 300 feet. Its rocks are mostly sandstone, but there are strata of _limestone in the Mississippi valley, and in the region w. and n. of Moosehead lake. Its most abundant fossils are spirifers, with other mollusks. There are no land-plants in the•New York and western beds, but lycopods occur in the upper limestones at Gaspe.
2. The Coniferous period. The cauda-galli grit, chiefly argillaceous sandstone, is 50 or 60 ft. thick in the Belderberg mountains of eastern New York. The name comes from a characteristic fossil sea-weed of feathery form. The rocks of the Sell°harie epoch are fine-grained calcareous sandstones, similar in quality and distribution to the preceding, but differing in their fossils, which are very numerous. The upper Helder berg is farther divided into the Onondaga limestone and the corniferous limestone— the latter taking its name from the presence of much imperfect flint or horn-stone (cornu, a horn). The corniferous limestones occur in New York, in Ohio along lake Erie, and throughout the Mississippi basin from Michigan to Kentucky, and from Ohio to Missouri. Its greatest thickness, in Michigan, is 854 feet. Its notable fossil plants are lycopods, conifers, and tree-ferns. This period was the coral-reef period of pakeo zoic times, and corals are found in great number and variety. The falls of the Ohio, at Louisville, are caused by such an ancient reef, and are rich in coral fossils. The
remains of vertebrates first appear in the corniferous epoch. They include relics of sharks, cestraciont and hybodont; of ganoids, having the body covered with shining plates of mail, now represented by the gar-pike; and of placoderms, having the body covered with bony plates, such as are worn by the turtles—fishes which seem to have linked the ganoidS with the sharks.
3. The Hamilton period includes the Marcellus shales, the Hamilton beds, and the Genesee shales. This formation extends across New York, its greatest thickness, 1500 ft., being e. of the center. It occurs southwardly to Tennessee, and westwardly to Iowa and Missouri; also in the valley of the Mackenzie, so that Meek believed that Devonian rocks are continuous from Illinois to the Arctic ocean, a distance of 2,500 miles. The Hamilton beds furnish superior flagging stones; the Genesee shales produce great quantities of petroleum, and occasionally of gas that may be used for heating and lighting. The vegetable fossils are lycopods, including lepidodendroids, and stigmaria, ferns, and conifers. The animal fossils still abound in corals and brachiopods; in this period appears the goniatites, the ancestor of the modern nau tilus. Among articulates we notice a new form of trilobite, and especially the earliest insect remains, in form akin to the ephemerte. Vertebrates are represented by fishes, like those of the corniferous period.
4. The epochs of the Chemung period are the Portage and The rocks of the lower, or Portage group, appear in western New York, having a thickness of 1000 ft. on the Genesee, and 1400 ft. on lake Erie. The Chemung rocks extend over the southern counties of the state, being about 1500 ft. thick near Cayuga lake. Far ther s., in Pennsylvania and beyond, they become 3,000 ft. thick. Ripple-marks, mud marks, and sun-cracked mud abound, indicating shallow seas, and lands alternately under, and out of, water. Sea-weeds and land-plants alternate.
5. The Catskill period produced shales and sandstones of various colors, chiefly red. This formation has a thickness of 2,000 to 3,000 ft. in the Catskills, and nearly 6,000 ft. in the coal regions of Pennsylvania, but thins out toward the west. It contains few fossils, and these not materially different from those of the lower periods. The Devo nian age closed with an epoch of great disturbance along the eastern border. The rocks were uplifted at various angles previous to the deposition of the carboniferous strata. The rising of Maine above the sea was probably completed during this age.