GLACIAL EPOCHS AND POLAR CLIMATES. ZZ 



ages before birds were evolved. This Glacial 

 Ej)och, however, did not consist of one gradual 

 change from a temperate to an ice climate which, 

 having reached its maximum, again passed slowly 

 away, but the earlier and later stages of the grand 

 phenomenon were broken up into several alternative 

 periods, during which warm and cold climates pre- 

 vailed respectively in the area affected every 10,500 

 years in the precession of the equinoxes during this 

 phase of the earth's high eccentricity. From the 

 commencement of this Glacial Epoch, the Migration 

 of birds, as we see it at the present time, was pro- 

 bably initiated. That these warm and cold Glacial 

 Periods actually took place, we have abundant 

 palaeontological evidence, even in the British Islands. 

 The fossilized remains of Hippopotami {Rhinoceros 

 hemitcechus) and Elephants {Eleplias antiquus) testify 

 to the uniform temperate climate with little or no 

 winter, just as the remains of Mammoths and Rein- 

 deer are indicative of a cold Arctic climate, with a 

 short hot summer and a long severe winter succeeding 

 it. There seems every inducement also to presume 

 that during the Glacial Epoch the ice, once formed, 

 never left the immediate regions of the Pole even 

 during the several warm inter-glacial periods, which 

 had such vast influence upon the climate of the 

 sub-arctic zone. 



From these remarks it may be gathered that we 

 do not require even the occurrence of one Glacial 

 Epoch to account for the Migration of birds. That 

 a habit so deeply rooted, so universal, and so vital 



