58 PRINCIPLES OF PALAEONTOLOGY. 



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. 



CHAPTER VI 



THE BIOLOGICAL RELATIONS OF FOSSILS. 



Not only have fossils, as we have seen, a most important 

 bearing upon the sciences of Geology and Physical Geography, 

 but they have relations of the most complicated and weighty 

 character with the numerous problems connected with the 

 study of living beings, or in other words, with the science of 

 Biology. To such an extent is this the case, that no adequate 

 comprehension of Zoology and Botany, in their modern form, 

 is so much as possible without some acquaintance with the 

 types of animals and plants which have passed away. There 

 are also numerous speculative questions in the domain of vital 

 science, which, if soluble at all, can only hope to find their key 

 in researches carried out on extinct organisms. To discuss 

 fully the biological relations of fossils would, therefore, afford 

 matter for a separate treatise ; and all that can be done here is 

 to indicate very cursorily the principal points to which the 

 attention of the palseontological student ought to be directed. 



In the first place, the great majority of fossil animals and 

 plants are " extinct " that is to say, they belong to species 

 which are no longer in existence at the present day. So far, 

 however, from there being any truth in the old view that there 

 were periodic destructions of all the living beings in existence 

 upon the earth, followed by a corresponding number of new 

 creations of animals and plants, the actual facts of the case show 

 that the extinction of old forms and the introduction of new 

 forms have been processes constantly going on throughout the 

 whole of geological time. Every species seems to come into 

 being at a certain definite point of time, and to finally disappear 

 at another definite point; though there are few instances 

 indeed, if there are any, in which our present knowledge would 

 permit us safely to fix with precision the times of entrance and 

 exit. There are, moreover, marked differences in the actual 

 time during which different species remained in existence, and 



