CHAPTER X 



THE MOST ANCIENT AND THE LIVING 



ANIMALS 



FOR many millions of years animals have existed 

 on the earth just as they exist today. But the 

 animals of past ages were not the same as the 

 animals we know at the present time. Some of them 

 were only slightly different from their modern rep- 

 resentatives, but some were very widely different. 

 Generally speaking, the further back we go in geo- 

 logic time the greater the difference between the ani- 

 mals then existing and those of the present day. 



The animals of the past are for the most part known 

 to us as fossils in the rocks. Fossils are the remains 

 or traces of animals or plants that formerly existed. 

 Fossils may be of any age. They may be the remains 

 of animals or plants that lived millions of years ago, 

 or only a few years previously. 



Once in the West Indies I was riding along a sandy 

 beach when suddenly I felt my horse to be on hard 

 rock instead of sand. There seemed to be no change 

 in the aspect of the beach, but when I dismounted I 

 found that that particular portion had been changed 

 to limestone rock in which were embedded several 

 different kinds of shells and the remains of various 

 other sorts of marine animals. 



But this portion of the beach had not been rock for 

 very many years, as some of the shells still had cling- 



