1874.] Climate of the Glacial Period. 435 
India and Australia. In the Lower Miocene beds of Swit- 
zerland, the flora of which has been wonderfully preserved on 
the northern borders of the Lake of Geneva, there are still 
species of fig, cinnamon, palm-trees, and other subtropical 
vegetation, but with them appear species of poplar, horn- 
beam, oak, elm, and other trees now characteristic of tem- 
perate climes, which are absent from the European Eocene 
strata, and which indicate a less tropical climate. These 
beds are succeeded by the Upper Miocene strata of Géningen, 
still containing many exotic genera, but with a still larger 
proportion of species that betoken that the climate—though 
still more equable and warm than at present—was gradually 
becoming unsuitable for subtropical plants. Coming still 
higher in the Tertiary series, we find in the Lower Pliocene 
of Italy that most of the subtropical genera have disap- 
peared, and when we reach the Newer Pliocene deposits the 
trees and shrubs are those now chara¢teristic of European 
forests, and suggest that the climate was similar to that 
at present enjoyed in Europe. Then in England we find 
the Newer Pliocene beds, with their trees and plants of 
recent species, as in the Cromer Forest bed, followed by 
lignite beds at Bure and Westleton, containing Salix 
polaris, now only known within the arctic circle, and Hynum 
turgescens, an arctic moss. M. Nathorst, a Swedish geolo- 
gist, who has studied these beds, considers that there is a 
gradual passage from the mild period of the forest bed, pro- 
bably only a little colder than at present, to severe arctic 
conditions. ‘These Bure and Westleton beds are succeeded 
by the till and boulder clay of the Glaciai period. 
If instead of the successive floras we follow the successive 
faunas, the land animals or the marine, we have a precisely 
similar succession of events, a gradual transition from 
the tropical forms of the Eocene and the subtropical 
ones of the Miocene through the more temperate species of 
the Pliocene, up to the arctic shells and mammals that 
usher in the Glacial epoch. The evidence is complete that 
points to the gradual cooling of the climate, and there is 
none whatever to show that there were any alternations of 
cold and warm periods. It is exa¢tly the same kind of evi- 
dence as we should have if we travelled from the tropics 
along the coast of the continent of America northwards. 
The plants and land animals on the one hand, the inhabi- 
tants of the deep on the other, would gradually change 
their character ; tropical forms would give place to sub- 
tropical, these to temperate, and finally, when the far north 
was reached, arctic species would predominate. 
