56 PRINCIPLES OF PALEONTOLOGY. 



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 pal3eontological evidence, that the 

 greater part of the North Temperate Zone, at a comparatively 

 recent geological period, has been visited with all the rigours 

 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 lusus natures, due to some 

 "plastic virtue la'ent 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. 



