BEFORE AND AFTER 77 



studying the climate was mostly warmer than at the pres- 

 ent day. The climate of the Eocene was tropical. The 

 Miocene was sub-tropical and becoming cooler. Palms 

 become rarer in the Upper strata. Evergreens, which 

 form three-fourths of the flora in the Lower Miocene, 

 divide the flora with deciduous trees in the Upper. And 

 through the Pliocene the climate, though still warmer 

 than now, was steadily becoming cooler ; till in the 

 beginning of the next period, the Pleistocene, it had 

 become considerably colder than that of the present day. 

 And then followed a time which is known as the great 

 Ice Age, or the Glacial Period, a time which has left its 

 traces all over this country, and, indeed all over Northern 

 Europe and America, and even into southern lands. The 

 cold increased, heavy snowfalls piled up snow on the 

 mountains of Wales, the Lake District, and Scotland ; 

 and the snow remained, and did not melt, and more fell 

 and pressed the lower snow into ice, which flowed down 

 the valleys in glaciers, as in Switzerland to-day. Gradually 

 all the vegetation of temperate lands disappeared, till 

 only the dwarf Arctic birch and Arctic willows were to be 

 seen. The sea shells of temperate climates were replaced 

 by northern species. Animals of warm and temperate 

 climates wandered south, and the Arctic fox, and the 

 Norwegian lemming, and the musk ox which now lives in 

 the far north of America took their place ; and the 

 mammoth, an extinct elephant fitted by a thick coat of 

 hair and wool for living in cold countries, and a woolly- 

 haired rhinoceros, and other animals of arctic regions 

 occupied the land. When the cold was greatest, the 

 glaciers met and formed an ice-sheet ; and Scotland, 

 northern England and the Midlands, Wales, and Ireland 

 were buried in one vast sheet of ice as Greenland is to-day. 

 How do we know this ? To tell how the story has been 

 read would be to tell one of the most interesting stories 

 of geology. Here we can only give the briefest sketch of 



