DI VISIONS OF TILE DEVONIAN SYSTEM. At the beginning of the Devonian period the dry land of was confined to the present ter ritory 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 Saint Lawrence were merely outlined. and the Ottawa had begun its work in the Archaean region between the Saint Lawrence and Labrador. The Devonian period was characterized by a series of oscillations of level, the amplitude of the variations, and the subsequent thicknesses of deposit being greater in the eastern part. The inland sea opened south into the Gulf of Mexico, north into the Arctic Sea, and covered all the northern central region of the present continent with shallow lagoons, separated by low, sandy areas.
The distribution of the several divisions is as follows: (1) The Oriskany sandstone extends from near Oriskany. Oneida County. N. Y.. southwest along the Appalachian-. into Pennylvania, Maryland, and Virginia. It appears near Buffalo, in Can ada. near Waterloo, in Ohio, in Indiana, southern Illinois. and Missouri. Its thickness at Oriskany is about :30 feet; in Illinois, 250 to 300 feet. Its rocks are mostly but there are strata of limestone in the Hudson Valley, and in the region west and north of Moosehead Lake.
(2) The Coniferotk series, of which the lower member, the Seholiarie stage. includes the canda-galli grit and the Schoharie grit. The former is an argillaceous limestone, occurring in the ilelderberg Mountains of eastern New York, and takes its name from a characteristic fossil sea-weed of feathery form. The S•hoharie grit is similar in character and distribution, but differs in its fossils. which are very numerous. The upper member of the Cornifcrous is divided into the Onondaga limestone and the corniferons limestone. the latter taking its name from the presenee of inueli imperfect flint or horn-stone. The eorniferous limestones neeur in New York, in Ohio along Lake Eric. and throughout the Mississippi basin from Michigan to Kentucky. and from Ohio to Missouri. Its•greatest thick ness, in Michigan, is 3.34 feet. Its notable fossil plants are lyeopods, conifers, and trce•ferns. This period was the coral-reef period of Paleozoic 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.
(3) The Hamilton series includes the INfar cellus shales, the Hamilton beds, and Hie I;eile see shales. This formation extends across New York, its greatest thickness:, 1501_) feet, being east of toe centre of the State. It occurs south wardly to Tennessee. and Nve...t. wa rdly to town and Missouri; also in the valley of the Macken zie, so that .leek believed that Devonian rocks are continuous from Illinois to the Arctic Ocean, a distance of '2500 miles.
(4) The stages of the Chemung series are the Portage and the Chemung. The rocks of the
lower, or Portage group, appear in western New York, having a thickness of 1000 feet on the Genesee, and 141)0 feet on Lake Erie. The ('he lining rocks extend over the southern counties of the State. being about 1300 feet thick near Cayuga Lake. Farther south in Pennsylvania and beyond. they become 3000 feet thick. Nipple marks, mud marks, and sun-cracked mud abound, indicating shallow seas, aril lands alternately under :and above water. The eastward extension of the upper Devonian rocks consists of sand stones and conglomerates, and were formerly con sidered a separate epoch, called 'Catskill.' They are now thought to be the shore deposits of the Portage and Chemung strata.
The life of the Devonian was abundant. but chiefly marine. Sea-plants, such as ftwoids, con tinued up from the Silurian. and land-plants appeared, ineludhig ferns, lyeopods. conifers, and equisetz•, many of them being of large size. Some, indeed, are so well preserved that the cellular structure of the wood is observable in their section-. Among the animals great variety abounded. Crinoids of the blastoid or budlike type, also the plumose ones; brachiopods were not lacking, especially the long-winged species: there were also the early forms of ammonites, trilobites, and insects. An important development is the first a ppea ranceof vertebrates—fishes. wh ich fairly swarmed in the Devonian seas. They in elude relics of sharks. eestraeiont, and hybodont of ganoids. whose modern representative is the gar-pike. having the body covered with shining plates of mail, and of placoderms. having the body covered with bony plates, such as are worn by the turtle-fishes which seem to have linked the ganoids with the sharks. Among the genera were Cepholaspis (q.v.). Pterielithys Coecostens (q.v.), Dinichthys The latter. found in the Ohio Devonian, was at least I feet long; another, Titani•hthys, probably reached 30 feet. Both were covered with heavy plates.
The Devonian rocks are of vast importance. economically. for they contain the great stores of petroleum and natural gas obtained in Penn sylvania. New York. West Virginia. and other Appalachian States. The Hamilton beds contain flagging stones of superior quality, while the Coniferous yields lime and cement materials.
In Great Britain Hie Devonian system includes sandstones, slates. and limestones similar in general character to those appearing in Anwriea. The 'Old Red Sandstone.' a freshwater phase of the Devonian in Scotland, admirably dc scribed by thigh Miller. is the British equivalent of the Catskill series. .\ large area of 1)evonian rocks is found in northern Prance, Belgium, and North t:ermany. also in Itussia, l'hina. and Anst ralia.
Butt tiadtArti Y. Dana, Manual of qeology (4t 11 ed., New York, 189(11; t:eikie, 'lust-Book t;,oloyy. 'London, ltitt:t) ; \\*Minn's, "The De vonian and Carboniferous," Bulletin 80, United Motes (;.oblietti ,t•_:uri•cy (1Vashington, 18)1).