Trilobite (Asaphus candatus), (from the Silurian).
Orthoceras subannulatum (from the Silurian).
5. Cambrian. Under this term, derived from the old name for Wales, are included many sandstones, grits, slates and flags, with here and there a limestone band. They form the greater part of the western counties of Wales, where they rise to a considerable height above the sea level. The highest hills of Westmoreland and more than half of Scotland are composed of beds of this age.
The fossils, save in the limestone bands, are not easy to find, but in places they are fairly abundant. Brachiopods are far more numerous than the Mollusca properly so-called. Of these, the genus Orthis was most abundant at about the close of this period. Certain beds of this age have received the name of Lingula Flags, owing this prevalence in them of the curious Brachiopod Lingula so like the species now living in some of the warm seas of the tropics. The Trilobites included several forms, and one species (Paradoxides Davidis) attained the length of nearly two feet. A few star-fish, some Hydrozoans (Graptolites), and the tubes and casts of Annelides and tracks of Trilobites, complete the list of more remarkable fossils. The subdivisions of the Cambrian rocks will be found in the table on p. 16.
6. Pre-Cambrian.—Near St. David's Head and some other places in Wales, in Anglesea, Shropshire, etc., some yet older rocks have been found. They are probably for the most part of volcanic origin, but they have been so much changed since they were first deposited, and as hitherto no fossils have been found in them, little is known concerning them.
Parts of the western coast of Northern Scotland and the Hebrides are composed of a crystalline rock called Gneiss, and supposed to be the oldest member of the British strata. No fossils have been found in it.
Skull of Deinotherium giganteum, a huge extinct animal, related to the elephants (from the Miocene of Germany).