Fig. 651.—Section across Snowdon.
A, Fossiliferous grits (Bala series); B, Greenstone (intrusive); C, Porphyry; D, Volcanic ashes, sometimes calcareous and fossiliferous Bala limestone.
Fig. 652.—Silurian fossil.
The Silurian system was so named by Sir. R. Murchison, after the territory formerly occupied by the Silures, but the system is, of course, universal. We have here sandstones, limestones, and shales, deposits lying upon the Welsh slate. The Upper and Lower Ludlow beds, and the “May Hill” sandstone, then the Lower Silurian, with Caradoc beds, and the Tremadoc slate, etc. In this system volcanic action is observable, and all the organic remains are those of marine animals, such as corals, shell-fish, marine worms, encrinites, molluscs, and other zoophytes in great variety. We find also a number of graptolites, trilobites, echinus (sea-urchin), terebratula, and many other forms.
Fig. 653.—Trilobite.
Fig. 654.—Terebratula.
The Trilobites were amongst the first creatures inhabiting our globe, and it is a curious fact to contemplate, that their eyes (fig. 655) should have been preserved perfect; they present one of those wonderful objects which carry one’s thoughts backwards to the early ages of the world, probably many millions of years, and yet it is found by the peculiar structure of the eyes of these Trilobites that they were placed at the bottom of the sea with perfect power to look upwards at the light of the sun through the transparent waters. The same hand and the same power had then Divine care and solicitude for the well-being of His creatures, as great as He has for those of later ages, and these animals are mentioned in Genesis—“Let the waters bring forth abundantly the moving creature that hath life.”
