94 AN INTRODUCTION TO ZOOLOGY. 



but only by the agency of water ; they therefore can 

 only represent the inhabitants of t}ie land by a 

 chance fragmentary specimen ; nor is it likely that 

 rocks of any age completely represent the climatic 

 regions even of the faunas of the seas. Again, the 

 stratified rocks of one age are constantly being de- 

 stroyed by the denudation of a subsequent period. 

 Not only so, but when we consider that all our 

 quarrying and exploring is but an infinitely insignifi- 

 cant process of nibbling at the edges of the huge 

 fields of rock which contain the buried record of past 

 ages of life, it must be obvious that much remains 

 for future workers to discover. From the imperfect 

 record of the past that we have at our command, we 

 cannot therefore hope to get the story of the develop- 

 ment of life arranged in a neat set of consecutive 

 chapters, like the novelette that runs through the 

 successive pages of a popular magazine. But allow- 

 ing for the necessary imperfection of the record, we 

 do get a series of fossil forms presented by the 

 ascending series of rocks, that bears ample evidence 

 to the general truth of the Darwinian views. ^ 



It must be clearly borne in mind that the develop- 

 ment of new and more highly organized forms does 

 not by any means imply the extinction of the simpler 

 type from which they have been derived. We have 



' Thus, e.g., fishes are found to precede reptiles in the 

 geological record, while reptiles again precede birds and 

 mammals. 



