74 DOCTRINE OF EVOLUTION 



and it interprets them through its knowledge of the 

 way modern animals are constructed and of the changes 

 the earth's crust has undergone. A skull-like object 

 may be found in a coal field and may come into the hands 

 of the palaeontologist : from his acquaintance with the 

 head skeletons of recent types he will be able to assign 

 the extinct creature which possessed the skull to a defi- 

 nite place in the animal scale and to understand its 

 nearer or wider affinities with other animals of later 

 times and of earlier epochs. In doing these things 

 palaeontology employs the methods of comparative 

 anatomy with which we have now become familiar. 

 In the performance of its other tasks, however, palaeon- 

 tology must work independently. It is necessary to 

 know when a fossilized animal lived, not that its time 

 need be measured by an absolute number of a few 

 thousands or millions of years antedating our own era, 

 for that is impossible. But the important thing is to 

 know its relative age, and whether it preceded or * 

 followed other similar animals of its own group or of 

 different divisions. The rocks themselves must be 

 understood, how they have been formed and how they 

 are related in mineralogical nature and in historical 

 succession. Palaeontology also deals with a number of 

 subjects that are not in themselves biological, such as 

 the combination of circumstances necessary for the 

 adequate preservation of fossil relics. In so far as it is 

 concerned with physical matters, as contrasted with 

 strictly biological data, it is one with geology. Indeed, 

 the investigators in these two departments must always 

 work side by side and render mutual assistance to one 

 another in countless ways, for each division needs the 



