CONCLUSIONS TO BE DRAWN FROM FOSSILS. 43 



c. In the case of marine animals, we are as yet very far from 

 knowing the exact limits of distribution of many species within 

 our present seas ; so that conclusions drawn from living forms 

 as to extinct species are apt to prove incorrect. For instance, 

 it has recently been shown that many shells formerly believed 

 to be confined to the Arctic Seas have, by reason of the ex- 

 tension of Polar currents, a wide range to the south ; and this 

 has thrown doubt upon the conclusions drawn from fossil 

 shells as to the Arctic conditions under which certain beds 

 were supposed to have been deposited. 



d. The distribution of animals at the present day is certainly 

 dependent upon other conditions beside climate alone ; and 

 the causes which now limit the range of given animals are 

 certainly such as belong to the existing order of things. But 

 the establishment of the present order of things does not date 

 back in many cases to the introduction of the present species 

 of animals. Even in the case, therefore, of existing species of 

 animals, it can often be shown that the past distribution of the 

 species was different formerly to what it is now, not necessarily 

 because the climate has changed, but because of the alteration 

 of other conditions essential to the life of the species or con- 

 ducing to its extension. 



Still, we are in many cases able to draw completely reliable 

 conclusions as to the climate of a given geological period, by 

 an examination of the fossils belonging to that period. Among 

 the more striking examples of how the past climate of a region 

 may be deduced from the study of the organic remains con- 

 tained in its rocks, the following may be mentioned : It has /. 

 been shown that in Eocene times, or at the commencement 

 of the Tertiary period, the climate of what is now Western 

 Europe was of a tropical or sub-tropical character. Thus the 

 Eocene beds are found to contain the remains of shells such 

 as now inhabit tropical seas, as, for example, Cowries and 

 Volutes ; and with these are the fruits of palms, and the 

 remains of other tropical plants. It has been shown, again, - 

 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 palaeontological evidence, that the 



