THE WINTER REST. 109 



hedgehog, which similarly retire for the sake of 

 warmth far beneath the soil. 



This practice of the winter sleep of plants and -^/ 

 animals, however, though now so familiar to all of 

 us in northern climates, is, geologically speaking, ^^ — 

 a comparatively modern and recent habit. Du- 

 ring by far the greater part of this planet's exis- ; 

 tence winter has been absolutely unknown over 

 its whole surface, from the poles to the equator ; 

 and tropical vegetation, with a tropical fauna,' 

 reigned supreme even within the Arctic Circle. / 

 It was only at the very close of what geologists 

 I call the Tertiary Period that any indications of 

 I) chilling at the extreme north and south ends of 

 this oblate spheroid of ours began to display them- 

 i selves, and winter and summer first took their 

 ! present form. Up to that epoch, therefore, all 

 "the trees on the earth had been evergreens, as 

 they still are within the tropics, mostly of the 

 large-leaved type represented now in our own 

 shrubberies by the laurels, the laurustines, and the 

 Japanese aucubas. But with the setting in of 

 that long cold spell, known as the Glacial Epoch 

 or the Great Ice Age, all this was rapidly reversed. 

 Plants and animals alike, finding themselves face 

 to face with hitherto unknown chilly conditions, 

 had either to accommodate themselves to the new 

 circumstances or to die out altogether. Many 

 kinds among them, it seems, were unable to 



