INTRODUCTION 



From the earliest times it has been known that bodies 

 resembling marine animals occur embedded in the rocks. 

 For several centuries two distinct views were held respect- 

 ing their nature. By some persons they were thought 

 to have once formed parts of living animals, and con- 

 sequently to indicate that the spot where they are now 

 found was in past ages covered by the sea. Others, feeling 

 it difficult to account for so much geographical change as 

 would be necessitated by this view, considered that they 

 were not of organic origin at all, but had been formed by 

 some ' plastic force ' within the earth — that they were in 

 fact ' Sports of Nature.' Since, however, these bodies re- 

 semble in every essential respect the hard parts of animals 

 now existing, we may at once reject this hypothesis. 



The remains of animals and plants of past ages pre- 

 served in the rocks are known as fossils, the study of which 

 forms the subject of Palaeontology. 



In order that an animal or plant may become a fossil 

 two conditions are generally necessary : First, it must 

 possess a skeleton of some kind or other, since the soft 

 parts are rapidly decomposed ; consequently such animals 

 as jelly-fishes leave no trace of their existence, unless it be 

 a mere imprint. Secondly, the organism must be covered 

 up by some deposit, otherwise it will soon crumble to pieces 



w. p. 1 



