56 PRINCIPLES OF PALAZONTOLOGY. 
that in Miocene times, or about the middle of the Tertiary 
period, Central Europe was peopled with a luxuriant flora 
resembling that of the warmer parts of the United States, and 
leading to the conclusion that the mean annual temperature 
must have been at least 30° hotter than it is at present. It 
has been shown that, at the same time, Greenland, now buried 
beneath a vast ice-shroud, was warm enough to support a large 
number of trees, shrubs, and other plants, such as inhabit the 
temperate regions of the globe. Lastly, it has been shown, 
upon physical as well as paleontological evidence, that the 
greater part of the North Temperate Zone, at a comparatively 
recent geological period, has been visited with all the ngours 
of an Arctic climate, resembling that of Greenland at the pre- 
sent day. This is indicated by the occurrence of Arctic shells 
in the superficial deposits of this period, whilst the Musk-ox 
and the Reindeer roamed far south of their present limits. 
Lastly, it was from the study of fossils that geologists learnt 
originally to comprehend a fact which may be regarded as of 
cardinal importance in all modern geological theories and 
speculations—namely, that the crust of the earth is liable to 
local elevations and subsidences. For long after the remains 
of shells and other marine animals were for the first time ob- 
served in the solid rocks forming the dry land, and at great 
heights above the sea-level, attempts were made to explain this 
almost unintelligible phenomenon upon the hypothesis that 
the fossils in question were not really the objects they repre- 
sented, but were in truth mere /wsus nature, due to some 
‘plastic virtue latent in the earth.” The common-sense of 
scientific men, however, soon rejected this idea, and it was 
agreed by universal consent that these bodies really were the 
remains of animals which formerly lived in the sea. When 
once this was admitted, the further steps were comparatively 
easy, and at the present day no geological doctrine stands on 
a firmer basis than that which teaches us that our present con- 
tinents and islands, fixed and immovable as they appear, have 
been repeatedly sunk beneath the ocean. 
