DISTRIBUTION OF BIRDS IN TIME AND SPACE. 195 



badger, the mice and squirrels, the snakes and 

 lizards 1 



Now here will come in the value of our study of 

 the distribution of animals in time, showing us as 

 it does that the connection between the British 

 islands and the continent is still more intimate 

 than we at first suspected. For we learn now that 

 the bear, the wolf, the reindeer, the wild boar, 

 the beaver, and even the lion, elephant and 

 rhinoceros, once roamed in both areas. The 

 three last have disappeared more or less com- 

 pletely throughout the greater part of what we 

 call the Palsearctic region. The rest remain still 

 on the continent but have long since passed away 

 from amongst the British fauna. But how came 

 any of these to gain an entrance into these 

 islands 1 One or other of them might have 

 crossed by swimming, but we can scarcely 

 suppose all did. Our only other alternative 

 is to postulate a former land connection. For 

 confirmation on this point we turn to the 

 geologist, and we are supplied with an abun- 

 dance of the most convincing evidence, which 

 need not be discussed here. 



The distance of time which has elapsed since 

 two isolated areas of land were last in connection, 

 we gather approximately from the degree of dis- 

 similarity in the fauna of each. Thus, when the 

 date is comparatively recent, the diff*erences are 

 slight; when of great antiquity, they will be 

 found to be very great. 



For instance, as Mr Alfred Eussel Wallace 

 points out, the absence from Madagascar of al- 

 most all the characteristic mammalia, birds and 



