The Devonian system is represented in the British Isles, except in the extreme south of England, by a thick series of red sandstones, shales, and conglomerates. Red sandstone is the predominate outcropping rock, the colors of which range from light red to deep chocolate brown, but in places exhibit green, yellow, gray, and mottled tints. The series of formations which make up this system have been known collectively since the early days of geologic science as the Old Bed Sandstones.
In Cornwall and southern Devon the Devonian is represented by slates, grits, volcanic materials, and thick masses of limestone holding marine fossils; but in Ireland, Wales, Scotland, and the contiguous parts of England the formations of equivalent age constitute the totally different facies, the Old Red Sandstones. These show their contrast not only in lithologic character, but in their barrenness of marine fossils. The Devonian age of these rocks . . .