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a pine wood, a moor, a salt-marsh, or a sand dune ; the con- 

 ditions under which they live ; the features they have in 

 common ; the features in which they differ ; their relation- 

 ship to one another ; and their distribution over any district. 

 If plants are dependent on soil, climate, altitude, and other 

 factors, animals are also not only dependent on these, but 

 on the plants as well, factors which differ everywhere, not 

 only in different associations but in the same associations 

 occupying different localities. By thus noting in what these 

 fauna! groups agree, and in what they disagree, some sub- 

 stantial basis will be found for an adequate discussion of the 

 history of animals which in its turn is largely dependent 

 on the geological changes any area has undergone. To this 

 history we must now turn. 



V. — The History of the Terrestrial Fauna. 



The dynamical aspect of the fauna deals with its evolution, 

 and the history of the succession of faunas which have lived 

 within the district. It is a branch of zoology beset with 

 peculiar difficulties. The lack of data so apparent when 

 considering the statics of the fauna could easily be obtained 

 by further investigation. Not so with the dynamics of the 

 fauna, the full history of which can never be written because 

 the records have absolutely disappeared. Hence, an inter- 

 pretation of the land fauna must to a large extent be specula- 

 tive, for in this enquiry palaeontology helps us but little. 

 From it we learn, however, that the mammalia were once 

 extremely different from what they now are. The remains 

 found in the celebrated cave of Kirkdale proved that a 

 most extraordinary assemblage of mammals formerly lived in 

 North East Yorkshire. It seems probable that the occupants 

 of this hyaena den flourished in pre-glacial times, for the 

 mammalia found in the post-glacial peat bogs only include, 

 at any rate in Cleveland, the Red Deer, the Reindeer, the Wild 

 Boar, the Wild Ox, but not such animals as the Hyaena, 

 Mammoth. Rhinoceros, or Hippopotamus. 



Arguing from analogy, it seems reasonable to infer that 

 the insects of the pre-glacial period must have presented 

 similar features to the mammalia, that is, a strong mixture of 

 African and northern species, but of this we have no 

 pakoontological evidence. Nor does there seem to be any 



