286 THE STORY OF THE EARTH AND MAK. 



to a great and terrible revolution, whereby the old 

 Pliocene continents, with all their wealth of animals 

 and plants, became sealed up in a mantle of Green- 

 land ice, or, slowly sinking beneath the level of 

 the sea, were transformed into an ocean-bottom 

 over which icebergs bore their freight of clay and 

 boulders. We also saw that as the Post-pliocene 

 age advanced, the latter condition prevailed, until 

 the waters stood more than a thousand feet deep 

 over the plains of Europe. In this great glacial 

 submergence, which closed the earlier Post-pliocene 

 period, and over vast areas of the Northern Hemi- 

 sphere, terminated the existence of many of the 

 noblest forms of life, it is believed that man had 

 no share. We have, at least as yet, no record of 

 his presence. 



Out of these waters the land again rose slowly 

 and intermittently, so that the receding waves 

 worked even out of hard rocks ranges of coast 

 cliff which the further elevation converted into 

 inland terraces, and that the clay and stones de- 

 posited by the Glacial waters were in many places 

 worked over and rearranged by the tides and waves 

 of the shallowing sea before they were permanently 

 raised up to undergo the action of the rains and 

 streams, while long banks of sand and gravel were 

 stretched across plains and the mouths of valleys, 

 constituting (t kames," or " eskers," only to be 

 distinguished from moraines of glaciers by the stra- 

 tified arrangement of their materials. 



