DEVONIAN SYSTEM, a name in geology originally given to the rocks of Devonshire and Cornwall, England. This name was proposed by Murchison and Sedgwick to replace the more character istic and older term of Old Red Sand stone (a fresh water deposit), because the slaty and calciferous strata in Devon shire contain a much more copious and rich fossil fauna than the red arenaceous rocks of Scotland, Wales, and Hereford shire, with which they are believed to be contemporaneous. The fossils of the la custrine Old Red Sandstone are chiefly fishes which have been classed as Ganoids. Professor Huxley approximates them to the Siluridx; but investigations in prog ress in 1900, it is believed, will assign many of them to the lung fishes, repre sented in modern waters by Ceratadus and Lepidosiren, and others not repre sented in the waters of the modern world. The fossils of the marine De vonians are largely corals such as Fava sites and Cyathophyllum, with brachio pod shells and skeletal parts of other organisms.
The physical condition under which the marine sediments in Devonshire were de posited differed greatly from that which marked the accumulation of the Old Red Sandstone and has caused some doubts as to the correlation of the two sets of strata. British geologists retain both names, the Devonian System and Old Red Sandstone System; in the United States the term Devonian is used almost ex clusively. The strata intermediate be
tween the Silurian and Carboniferous consist of sandstones of different colors, calcareous slates, limestones, etc. They are divided into the Lower, Middle, and Upper Groups, all containing fossils; but in the middle division, corresponding practically to the Hamilton of New York, organic remains are especially abundant and include corals, crinoids, brachiopods, mollusks, and crustaceans.
Devonian rocks occupy a large area in central Europe, as well as in the United States, eastern Canada, and Nova Scotia. In the United States they are found in New York and Pennsylvania, and include sand and limestone, used as building ma terial, and are classed under the names of Oriskany, the oldest term, Corniferous or Upper HeEerberg, Hamilton, and Chemung. Devonian rocks appear in some regions of the Appalachian Moun tains. In the middle part of Michigan they surround the coal basin; and they are also found in Kentucky, Indiana, Ohio, Illinois, eastern Iowa, and Nevada. In Maine they are in a metamorphic con dition. In the Upper Groups of the De vonian System there are carbonaceous shales, which by mutual distillation give much of the petroleum and natural gas found in the sandstones of Pennsylvania and eastern Ohio.