Page:Popular Science Monthly Volume 9.djvu/306

284 European Continent. The Pacific bridge was where Behring's Straits now are.

These conclusions are deducible from the following facts:

1. Our American flora, which began in the Cretaceous, spread in the Tertiary age to Europe on the one hand, and to China and Japan on the other; and this could only have taken place when the continents were connected. The characteristic plants of this flora have been found fossilized on the Upper Missouri, on Mackenzie's River, Disco Island, Greenland, Iceland, the island of Mull, and on the continent of Europe as far south as Italy. No collection has been made of Tertiary plants in Japan and China, but the living flora of these countries contains a large number of species identical with those found, either living or fossil, in North America. The remarkable similarity between the flora of Northeastern Asia and that of America, so clearly shown by Prof. Gray, is such as to demonstrate a community of origin, and that its place of origin was America may be fairly inferred from the character of the present American flora and from the facts that a large part of the most characteristic genera are found here in the Cretaceous rocks, and many of the living species in our fresh-water Tertiaries.

2. Marine Tertiary deposits are almost completely absent from the arctic lands, while they now skirt or cover most tropical continents and islands.

Pocks containing marine Tertiary fossils are conclusive evidence of the submergence in Tertiary times of the land in the localities where they occur; and they would not fail to exist over great areas in the arctic, had the land there been more depressed in the Tertiary age than now; since most of the country which borders the Arctic Sea, both in America and Asia, lies but little above the sea-level.

The Tertiary strata, that have yielded more than three hundred species of land-plants at the far north are generally fresh-water and marsh deposits, containing fresh-water shells and beds of lignite similar to those of the central portions of our own continent. In contrast to the state of things thus indicated, the marine Tertiaries, which form the margins of our South Atlantic and Gulf States, the West Indies, the Isthmus, and the northern part of South America, are automatic records of high sea or low land level, in the tropical regions during Tertiary times.

These facts seem to prove that in the period when a warm-temperate climate prevailed over all the arctic regions, the land was broader and higher than now at the north, lower and narrower at the south; and that barriers did then exist which excluded the tropical ocean-currents from the arctic sea.

II. Just what the topography of the arctic regions was during the Glacial period, we have as yet no very full and accurate information. It has been generally supposed that at least certain areas in the