Page:Popular Science Monthly Volume 76.djvu/489

Rh states bordering the Gulf of Mexico. There to-day many tropical molluscan genera are found in the waters, and on the marginal coastal plain there is a mixture of palms, deciduous trees and conifers. This is just what we find in the fossil Eocene flora of California and Puget Sound; laurels, figs, sycamores, chestnuts, elms, liquidambar, oaks, palms and sequoias lived together. From this association we should infer that the climate of the west coast was no longer tropical, but subtropical, and very rainy.

The middle Tertiary faunas are very like the present in the association of genera, and the flora on the land agrees with this. The palms have disappeared, but laurels still occur. It is probable that the climate of the upper Miocene had about the same temperature as that of the present in California, but it had, apparently, a much greater rainfall, or one much more evenly distributed.

The Tertiary flora of the west coast was immensely richer than the present. No elm, liquidambar, nor true laurel lives wild on the west coast now, and many other types that flourished here are gone. The impoverishment of the present tree flora of California, as compared with that of the Tertiary, has been ascribed to volcanic activity, bur this is absurd. In the first place the great extinction of the old types took place in the lowering of temperature near the end of Eocene time, while the era of great lava outbursts on the west coast was after the middle of the Miocene. The climate continued to cool off in the Pliocene, as is shown by the northern types of mollusca that then ranged as far south as Los Angeles, and by the freshwater lake deposits of middle California, which contain a fauna at present confined to the Klamath region of northern California and southern Oregon. The flora of the Pliocene in California is very scanty, composed largely of willows, alders and conifers, very much like that of the Olympic Peninsula in Washington.

The constantly decreasing temperature throughout the Tertiary is sufficient to account for the reduction of the flora. The tropical and finally the warm-temperate types were killed off locally, and such as were confined to this region were wholly extinguished. Some of the forms that lived in more favored regions to the south returned after the Glacial epoch. But most of the region to the south of California is not favorable to the extensive growth of forests, and many of the types have never returned to California, except when brought in by man.

In the early Quaternary there were extensive ice-sheets in the Sierra Nevada, and probably the climate of the sea-coast was cool. The glaciers came down the slopes to a line that is now about 3,500 feet above sea-level; it is thought, however, that California stood considerably higher than now, and that conditions here were more like those of the present on the Olympic Peninsula.