334 PREHISTORIC EUROPE. 



upper or overlying strata ; while at the same time immigrants 

 from the north make their appearance and continue to increase 

 in number as we approach the more recent accumulations of 

 the Pliocene sea. Now and again, too, we come upon isolated 

 large stones which have in all probability been dropped from 

 floating - ice. Northern forms, such as the shallow - water 

 species, Mya truncata, Saxicava norvegica, and Buccinum un- 

 datum, made their way at this time even as far south as 

 Sicily. We may be sure that if such changes were taking 

 place in the water, the land could hardly escape similar ex- 

 periences. The southern forms of plants and animals would 

 disappear, some retiring to more genial latitudes, others be- 

 coming extinct, and as they vanished their vacant places would 

 be seized upon by the hardier tribes advancing from the north. 

 That not a few animals and plants became extinct at this time 

 we have every reason to believe. Amongst the former were 

 mastodon, hipparion, and many kinds of deer. The splendid 

 flora too suffered greatly, many of the forms dying out alto- 

 gether, while of those that survived to later times, the greater 

 number were more or less modified. The approach of the first 

 glacial epoch was heralded by the appearance of many animals 

 characteristic of the Pleistocene Period. Their appearance, 

 indeed, marks the close of the Pliocene. They were com- 

 mingled with certain Pliocene species, some of which struggled 

 on into interglacial times. Thus England in preglacial ages 

 was tenanted by elephants, rhinoceroses, hippopotamus, and 

 machairodus, by bears, Irish deer, and many other cervidse, by 

 urus, wild-boar, wolf, fox, beaver, and so forth. Of these, some 

 did not survive Pleistocene times, others outlived that period to 

 become extinct in the Neolithic Age, while yet others endured 

 all the changes and chances of the Glacial Period, and still form 

 part of the European fauna. 



Underneath the oldest known boulder-clay — that of Cromer 

 in Norfolk — occur certain fluvio-marine deposits, the plant- 

 remains in which bespeak the kind of climate that characterised 

 England at the commencement of the first glacial epoch. That 



