Page:Popular Science Monthly Volume 76.djvu/485

Rh Now while one swallow does not make a summer, one reef-building coral, or one palm, or one cyead does, since neither one of these organisms now lives outside of a warm climate.

All the Paleozoic sediments on the west coast are marine, and while the record is fragmentary, the evidence points uniformly to warm temperature of the sea, and, thus by inference, of the land. The Lower Cambrian, or Pre-Cambrian, glaciation of China and Australia has not been recognized in this part of the world, but this is merely negative, since land formations of that period are unknown here.

The Lower Cambrian limestones of Inyo County, California, and the adjacent region of Nevada, have extensive coral reefs of Archæocyathidæ; similar reefs are known in Europe and Australia, but not in the Arctic region.

In the Silurian of Plumas County, and the Devonian of Shasta County, California, there are coral reefs composed of Favositidse and Tetracoralla, and in both these ages similar reefs are known in Siberia and Alaska, which may show that the temperature of the sea had grown warmer in the middle Paleozoic, with a northward extension of the isotherms.

The Carboniferous of Shasta and Plumas counties, California, has great limestone masses full of reef-building Tetracoralla, and similar reefs are known up to 82° N\ lat., and down to the equator. Whatever the temperature was, it was remarkably uniform. The flora of the Coal Measures in the northern hemisphere indicates a warm and equable climate for the land, extending up into the Arctic region, and without evidence of any trace of climatic zones.

The Permian, or Upper Carboniferous, glaciation, which was so widespread in India, Australia, South Africa and South America, has not been recognized in North America. But this event is now recognized as the greatest catastrophe in geologic history, and its effects probably extended far beyond the limits of glaciation. With the accompanying lowering of oceanic temperature, near the end of the Paleozoic era, the ancient types of reef-building corals, the Favositidae and Tetracoralla, disappeared. Hardly anything but solitary corals, that may have been deep-water forms, are left in the Permian, and in the Lower Triassic no corals of any sort are known.

The Hexacoralla, the modern reef-builders, had already originated in the Paleozoic, but were then little developed, unspecialized types. They escaped the general catastrophe either by being distributed in regions where the destruction did not take place, or by being then