THE WEALDEN STRATA 19 



extinct animals and plants. And the best way is found 

 to be this. We give a name, generally formed from the 

 Latin or the Greek to a group of animals or plants, 

 which closely resemble one another ; the group we call 

 a genus. Then for the species, the particular kind of 

 animal or plant of the group, we add a second name to 

 the first. Thus, if we are studying the apple and pear 

 group of fruit trees, we call the general name of the group 

 Pyrus. Then the crab apple is Pyrus mains, the wild 

 pear P. communis, and so on. So that when you arrange 

 any of your species, and put down the scientific names, 

 you are really doing a bit of classification as well. You 

 are arranging your specimens with their nearest relations. 

 To return to our ancient river. With the logs and 

 trunks of trees, which the river brought down, came 

 floating down also the bodies of animals, which had lived 

 in the country the river flowed through. What kind of 

 animals? Very wonderful animals, some of them, not 

 like any living creature that lives to-day. By the time 

 they reached the mouth of the river the bodies had come 

 to pieces, and their bones vere scattered about the river 

 mouth. On the shore where we are walking we may find 

 some of these bones. But it is rather a chance whether 

 we find any in any one walk we take. The best time to 

 find them is when rough seas in winter have washed some 

 out of the clay, and left them on the shore. It is only 

 rarely that large bones are found here ; but you should 

 be able to find some small ones fairly often. The bones 

 are quite as heavy as stone, for a r . *he pores and cavities 

 have been filled with stone, generally carbonate of lime, 

 in the way we explained in describing the formation of 

 beds of limestone. This makes them quite different from 

 any present-day bones that may happen to lie on the 

 shore. So that you cannot mistake them, if once you 

 have seen them. They are bones of great reptiles, the 

 class of creatures to which lizards and crocodiles belong. 



