In Mr. Henry R. Knipe's scholarly and well-informed volume, _Nebula to Man_ (J. M. Dent & Co.), to which we are indebted not only for several of our illustrations but for many extremely valuable suggestions, the struggle for existence in the early ocean is well summed up:--
Thus through the brine life manifold proceeds, Impelled to higher states by growing needs; And all these early life-types in the seas Will branch in time to many species; And some amid conditions too severe, Must, after stress and struggle, disappear. And when a species falls from Life's domain It never gains a place on Earth again.
We may speculate with some approach to certainty on the general appearance of the earth in those days. There was far more water on the surface of the globe; the land surfaces were small and infrequent. The seas may have been shallower than those which we know, but they were far greater in extent. There must have been far more rain and a very much greater number of violent storms arising from the constant condensation of the waters by the rays of the sun. The sun was probably seen far less often in those days, and there are some geologists who believe the earth to have been perpetually covered with cloud, as the planet Venus is now.
Europe as a continent did not exist. A few islands showed their heads above the waves where Germany and Switzerland, Eastern France and Spain now stand. Scotland's rocky islets were probably visible, on the extreme west, though these islands were destined to sink again below the waves. Thence the ocean stretched without a break, as at present, to Canada. A great part of Canada's bleak lands was above the waters; but the United States, except for a few great islands, were submerged. In the southern hemisphere South America, split into numerous long reefs and islands, gave promise of the continent to be; and there were great stretches of land over Brazil, extending to the west where the great chains of mountains now rise. Asia was largely covered with shallow waters, and the whole extent of the northern plains of Africa was sea. So far as we are able to judge the distinctions of climates were less marked then than now, and the conditions seem to have been much more uniform over all the northern hemisphere. This equality of climate lasted into the next or Ordovician period.