Land-bridge from Northern Europe to North America. 35 
applicable to a transport in two directions, both from America to 
Europe as well as vice versa. 
The fact that both in America and Kurope the indigenous species of 
plants and animals identical to the two continents are largely confined 
to the coast region may appear at first sight in favour of the theory of 
introduction by birds. Almost all the American plants, and all the 
American freshwater sponges at any rate, occur in the vicinity of the 
coast. It has been argued, therefore, that, after their long flight 
across the ocean, birds would naturally alight on the earliest 
opportunity; and that it was for this reason that the plants and 
animals common to the two continents were so largely confined to the 
coastal districts. But from what has been mentioned we have no 
reason to infer that American birds do habitually alight on the west 
coast of Ireland on first reaching Europe. It seems highly probable 
that they cross by way of Greenland. We should, therefore, expect 
all species of the invertebrates and plants common to the two 
continents to be found in Greenland as well. This is not so. Only 
comparatively few of them are met with in Greenland. The theory 
that the resemblance in the fauna and flora of Eastern North America 
and Western Europe is due to the action of birds is, I think, not 
supported by sufficient evidence. 
The third theory, that the identical species on either side of the 
Atlantic Ocean are the result of a direct land-connexion between 
Scotland, Iceland, Greenland, and Labrador, appears to me to be well 
founded on geological, bathymetrical, and biological evidence. No 
decisive testimony, however, has as yet been brought forward to show 
during what geological period this land-bridge was formed and how 
long it lasted. The assumption that such geographical conditions 
prevailed during early Tertiary times is very widespread. That this 
state continued during the Miocene period is likewise maintained by 
many; though Professor Dawkins and a few others do not admit the 
existence of the northern land-bridge in Pliocene or more recent times. 
Sir Archibald Geikie’s researches point to the production of the great 
basalt plateaux of North-Western Europe in early Tertiary times. 
These plateaux formed a continuous tract of land, as far as the Farodes 
at any rate. He proves that in many places, such as Iceland, the 
Faroes, and the West of Scotland, enormous subsidence subsequently 
took place.’ 
Once we admit that animals and plants were able to survive the 
Glacial period in northern latitudes, a land-connexion such as suggested 
in Pliocene times would readily account for the presence of all the 
animals and plants common to Europe and America. By many of 
those best able to judge, an admission to that effect has been made. 
Pliocene deposits are scanty in the British Islands; yet they yield 
valuable suggestions as to the geographical conditions of the North 
Atlantic. An examination of the fossil invertebrates contained in the 
St. Erth Beds in Cornwall, which are of Pliocene age, showed that 
the fauna possessed a remarkably southern facies, and that there was 
1 W. Boyd Dawkins, Zarly Man in Britain, 1880, p. 43. 
2 A. Geikie, ‘‘ Basalt Plateaux of North-Western Europe’’: Q.J.G.S., 1896, lii, 
p. 405. 
