3. The lower old red sandstone consists of strata of red shale and sandstone, with beds of impure arenaceous limestone (eornstone). and frequently at the base great deposits of red conglomerate. The fossils peculiar to this division are the remarkable fish ceplia laspis, and the huge crustacea, of the genus Pierygotus, besides a few shells. To the south of the Grampians, the strata consists of a gray paving-stone and coarse roofing slate. The Devonian representatives of this section are tie sandstones and slates of the North Foreland, Linton, and Torbay, and the series of slaty beds and quartz ore sand stones developed on the banks of the Rhine near Coblentz. The Cephalaspis, so charac teristic of the cornstones, has been found in the Rhenish beds.
4. The tilestones or Ledbury Shales consist of finely laminated reddish and green micaceous sandstones, which have been noticed underlying the old red only on its western borders in Herefordshire. The fossils of those beds show a Silurian fauna with a num ber of old red forms; the tilestones are consequently referred sometimes to the one period, and sometimes to the other.
The old red sandstone occupies a considerable portion of the surface of Great Britain. In the north, it forms the boundary lands of the Moray firth ; beginning even as far north as the Shetlands and Orkneys, it covers the whole of Caithness, and in more or less broken tracts the east of Sutherland, Ross, and Cromarty, and the north of Inverness, Nairn, and Elgin. In the great central valley of Scotland it is the setting in which the coal measures are placed, stretching across the country on the one margin from Forfar to Dumbarton, and occurring on the other in separated tracts in Lanark and Berwick. In
the southern division of the island it is limited to a large triangular district in the south west. The apex of the triangle is at Wenlock, in Shropshire; a line thence to Start point, in Devon, would limit it on the east, and a second to Milford haven would do so on the west. The Bristol channel bisects it. A depression in the Welsh portion is occu pied with South Wales coal-field; and in a similar depression in Devon, the culm-beds are situated. In Ireland, strata of this age are found in the counties of Kilkenny. Water ford, Cork, and Kerry. The Devonian rocks have been carefully studied in Belgium and the Rhine district, and also in Russia, where they cover a larger district in the north of the empire. The American representatives of this period are extensively developed in New York, Pennsylvania, and Canada. The invertebrate animals found in the old red do not differ much from those of the Upper Silurian. Corals are remarkably abun dant and beautiful in the Devonian limestones. Goiniitites and Clymenia make their first appearance in this period, with several forMs of lower inollitsea. • Tillobites are still numerous. But the most striking feature in the period is the abundance of fish of curi ous forms, strongly protected outside by bard bony cases, or by a dense armor of gauoid scales.