Devonian System

Devonian System, so named by Murchison and Sedgwick from its occurrence in Devonshire, is a great series of sandstones, greywackes, slates, limestones, and associated volcanic rocks, 10,000 feet thick, between the Silurian and Carboniferous systems. It represents the more truly marine or open-sea type of deposits, on the whole contemporaneous with the Old Red Sandstone of other areas; but neither its passage downwards into the Silurian nor upward into the Carboniferous is well developed in England. It extends over Devon, Cornwall, Brittany, Belgium, the Rhine valley, the Harz, and the Alleghanies. Devonian rocks similar to those of Belgium are found in deep borings under London. The system includes valuable ornamental marbles and the killas or slate of Cornwall, the matrix of veins of lead, tin, copper, and iron, which metals are also worked in the Harz district. The fauna of these rocks includes the last few graptolites; numerous corals, especially Calceola sandalina; crinoids; trilobites, less varied than those of the Silurian; no less than 1,100 species of brachiopods, which class is represented by Stringocephalus Burtini and Spirifera disjuncta, and reaches its culmination during this period; ammonitids, such as Goniatites; nautilids, such as Orthoceras; and occasional remains of fish identical with those of the inland-water deposits of the Old Red Sandstone. The system in Europe is subdivided as follows: -

Upper. Condrusian or Famennian of Belgium, with the Cypridinia shales, amd the Pilton, Pickwell Down, and Cockington beds of Devon, and the Upper Old Red Sandstone of Scotland.

Middle. Eifelican, including the Frasnian, Rhynchonella cuboides beds, and Ramsleigh Limestone, and, below them, the Givetian, Stringocephalus Limestone, and Plymouth and Ilfracombe Limestone.

Lower. Coblenzian, Taunusian, and Gedinnian, the Lynton group of Devon and Lower Old Red Sandstone.