DEVONIAN. The name Devonian appeared in geological literature in 1839, when Murchi son and Sedgwick applied it to a rock system in Devonshire and Cornwall, England, con sisting of conglomerates, shales and fossilifer ous limestones below the Carboniferous rocks and above the great mass of the gray wacke or transitional series of Werner, that was already included in the Cambrian or Silu rian. Murchison and Sedgwick also included in the Devonian the Old Red Sandstone of Scotland. The Devonian Period is that part of Paleozoic time following Silurian and preced ing Carboniferous. At the beginning of the period, the seas were greatly restricted in North America, much as they were in the late Silurian (q.v.). Embayments existed on the present site of the Appalachians, and perhaps some what farther west. An arm of the Pacific also covered part of the Great Basin and other smaller embayments probably covered various areas. For the most part, however, the United States was land. By the middle of the period another great interior sea had encroached over a large part of central North America. Europe was also largely submerged in mid-Devonian. In Scotland and Wales were landlocked seas or lakes, and there were others in western Russia. A large part of central South America was covered by water. Fossil evidence indicates that in early Devonian there were land connections between North and South America and between South America and South Africa. Volcanic activity was extensive in western Europe, in New England and probably in California. Some folding took place ;^... northeastern North America, probably near the middle of the period. The rocks of the Devonian System in North America have been variously subdivided. H. F. Cleland (1916) gives the following as the New York type section, beginning with the lowest formations: Helderberg limestone, Oriskany sandstone, Onondaga limestone, Marcellus shale, Hamilton shale, Tully limestone, Genesee shale, Portage shale and sandstone, Catskill and Chemung sandstones. Where the line between the Silurian and Devonian systems should be drawn in North America is still a matter of dispute, the lower Helderberg formation being variously assigned to the Silurian and to the Devonian. In eastern United States Devonian
rocks outcrop extensively in New York and south ward throughout the Appalachian Mountains and plateaus. In the central Mississippi Valley Devonian is present but very thin. In Manitoba and the Northwest Territory, Canada, the Devo nian System includes limestones and shales and is of moderate thickness. There is an area of Devonian rocks extending along the Rocky Mountains from Montana across Alberta. In the United States the Devonian rocks of the Rocky Mountains appear in Colorado and Arizona.
In England and on the Continent the Devonian System presents two different classes of rocks : (1) the Old Red Sandstone, occurring in Scotland, in South Wales and across the Welsh border in England, also in the Baltic provinces of Russia and in Spitzbergen; (2) the marine i Devonian, occurring in southwest Eng land, n northern and southern France, in Spain and over large areas in Germany and central Russia. The Old Red Sandstone was laid down perhaps in shallow seas either closed or having only slight connection with the open ocean—perhaps in part on land in desert areas. The formation is of interest from its containing remains of Devonian land animals and plants. The rocks are fine-grained conglomerates, sand stones and shales. The marine Devonian of Europe is largely limestone, with some shales and slates.
Devonian rocks in Asia are found over a vast area in Siberia and also occur in China and in Asia Minor. In Africa they are found both in the northern and southern parts of the conti nent In South America Devonian rocks form a great system, being found in Brazil, Bolivia and the Falkland Islands.
The vegetable and animal life of Devonian time, so far as can be determined, did not differ greatly from Silurian forms, though it shows a general advance toward more highly developed types. The land vegetation included crypto gams and gymnosperms. Of the cryptogams the tree-ferns and the giant club-mosses (Lepidodendra) must have been conspicuous in the forests, being over 50 feet high. Of the gymnosperms, cycads, now almost extinct, were abundant, and it is possible that conifers of the yew family grew upon the higher ground.