THE DISTRIBUTION OF ANIMALS AND PLANTS. 493 
preserved. The study of the fossils of the latter Tertiary 
deposits led us to some singular conclusions. In Greenland 
there was a lignate bed of Miocene age. It abounded in fossil 
plants, many of them belonging to species still in existence. 
But where were these species living ? In such widely dis- 
severed areas as South Carolina, Japan, the Cape of Good 
Hope, and even Australia. Then, again, they found that our 
modern titles of old and new worlds were quite the opposite 
of the truth. During the Tertiary period the flora of Europe 
was made up of species now principally living in America, 
so that the new world in this respect was really the old. The 
fossil plants in Greenland indicated a warm temperature, 
so that the great ice-cap which covered the whole of the Arctic 
region had not then been formed. Its formation was of a later 
date, and the lecturer here produced abundant evidence to 
show how, after this ice-cap had been formed, it increased to 
such a degree that Great Britain laboured under an Arctic 
climature. The whole of the northern hemisphere underwent 
a long rigorous winter of many scores of thousands of years. 
They would see that, as this rigorous climate advanced over 
temperate regions, animals and plants unsuitable to the cold 
would have to migrate before it. This was the reason why 
hundreds of plants of Arctic species — i.e. of the same kinds 
as those now living in the lowlands of Scandinavia, Lapland, 
and even Spitzbergen — were now found on the tops of our 
highest English and Scottish mountains, as well as on the 
higher parts of the Swiss Alps and the Pyrenees. One very 
important illustration of the increased cold over temperate 
latitudes during the glacial epoch was the occurrence of seals 
in the Caspian Sea and in Lake Baikal, the latter situated in 
the very centre of the Asiatic continent. The Caspian Sea 
was completely isolated, and its waters had only one third the 
saline properties of ordinary sea-water. Baikal was purely a 
fresh-water lake, and yet the two species of seals living in these 
isolated waters belonged one of them to the same species as 
that frequenting the northern coasts of Britain, and the 
other to a species exceedingly abundant in the North Atlantic. 
How had they become isolated ? A knowledge of physical 
geography showed us that a depression of 500 feet would 
bring the® Arctic Sea once more over the areas of the 
Caspian Sea and Lake Baikal, as it had once spread there. 
The fact was that subsequent to this extension of the Arctic 
Ocean the whole of Asia was raised to its present position, 
and the lowest hollows had become occupied by water in 
which these two species of seals had become shut off from 
their oceanic fellow s, their habits being gradually accommo- 
xliv. 35 
