Page:Popular Science Monthly Volume 15.djvu/618

 a small fraction of the material so removed, for the sea of that ancient time spread over nearly the whole of Europe eastward into Asia, and everywhere received a tribute of sand and mud from the adjoining shores.

There is perhaps no mass of rock so striking in its general aspect as that of which this northern embryo of Europe consisted. It lacks the variety of composition, structure, color, and form, which distinguishes rocks of more modern growth. But in dignity of massive strength it stands altogether unrivaled. From the headlands of the Hebrides to the far fiords of Arctic Norway it rises up grim and defiant of the elements. Its veins of quartz, feldspar, and hornblende project from every boss and crag like the twisted and knotted sinews of a magnificent torso. Well does the old gneiss of the north deserve to have been made the foundation-stone of a continent.

Whether vegetation clothed this earliest prototype of Europe, and, if so, what were its characters, are questions to which at present no answer is possible. We know, however, that the shallow sea which spread from the Atlantic southward and eastward over most of Europe was tenanted by an abundant and characteristic series of invertebrate animals—trilobites, graptolites, cystideans, brachiopods, and cephalopods, strangely unlike on the whole to anything living in our waters now, but which then migrated freely along the shores of the Arctic land between what are now America and Europe.

The floor of this shallow sea continued to sink until over Britain at least it had gone down several miles. Yet the water remained shallow because the amount of sediment constantly poured into it from the northwest filled it up about as fast as the bottom subsided. This slow subterranean movement was varied by uprisings here and there, notably by the outburst at successive periods of a great group of active submarine volcanoes over Wales, the Lake District, and the south of Ireland. But at the close of the Silurian period a vast series of disturbances took place, as the consequence of which the first rough outlines of the European Continent were blocked out. The floor of the sea was raised into long ridges of land, among which were some on the site of the Alps, the Spanish Peninsula, and the hills of the west and north of Britain. The thick mass of marine sediment was crumpled up, and here and there even converted into hard crystalline rock. Large inclosed basins, gradually cut off from the sea, like the modern Caspian and the Sea of Aral, extended from beyond the west of Ireland across to Scandinavia and even into the west of Russia. These lakes abounded in bone-covered fishes of strange and now long extinct types, while the land around was clothed with a club-moss and reed-like vegetation—Psilophyton, Sigillaria, Calamite,etc.—the oldest terrestrial flora yet known in Europe. The sea, dotted with numerous islands, appears to have covered most of the heart of the continent.