284 THE POPULAR SCIENCE MONTHLY. 



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 con- 

 tinents 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 con- 

 tinent 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 dejjosits 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 simi- 

 lar 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 au- 

 tomatic 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-tem- 

 perate 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 informa- 

 tion. It has been generally supposed that at least certain areas in the 



