CONCLUSIONS TO BE DRAWN FROM FOSSILS. 55 



head are really based upon the present distribution of animal 

 and vegetable life on the globe, and are therefore liable to be 

 vitiated by the following considerations : 



a. Most fossils are extinct, and it is not certain that the 

 habits and requirements of any extinct animal were exactly 

 similar to those of its nearest living relative. 



b. When we get very far back in time, we meet with groups 

 of organisms so unlike anything we know at the present day as 

 to render all conjectures as to climate founded upon their sup- 

 posed habits more or less uncertain and unsafe. 



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, 



