ON A PIECE OF CHALK 71 



Nor have these wonderful metamorphoses of sea into land, 

 and of land into sea, been confined to one corner of England. 

 During the chalk period, or "cretaceous epoch," not one of 

 the present great physical features of the globe was in exist- 

 ence. Our great mountain ranges, Pyrenees, Alps, Hima- 5 

 lay as, Andes, have all been upheaved since the chalk was 

 deposited, and the cretaceous sea flowed over the sites of Sinai 

 and Ararat. 



All this is certain, because rocks of cretaceous, or still 

 later, date have shared in the elevatory movements which 10 

 gave rise to these mountain chains ; and may be found 

 perched up, in some cases, many thousand feet high upon 

 their flanks. And evidence of equal cogency demonstrates 

 that, though, in Norfolk, the forest-bed rests directly upon the 

 chalk, yet it does so, not because the period at which the forest 15 

 grew immediately followed that at which the chalk was 

 formed, but because an immense lapse of time, represented 

 elsewhere by thousands of feet of rock, is not indicated at 

 Cromer. 



I must ask you to believe that there is no less conclusive 20 

 proof that a still more prolonged succession of similar changes 

 occurred, before the chalk was deposited. Nor have we any 

 reason to think that the first term in the series of these 

 changes is known. The oldest sea beds preserved to us are 

 sands, and mud, and pebbles, the wear and tear of rocks 25 

 which were formed in still older oceans. 



But, great as is the magnitude of these physical changes 

 of the world, they have been accompanied by a no less striking 

 series of modifications in its living inhabitants. 



All the great classes of animals, beasts of the field, fowls of 30 

 the air, creeping things, and things which dwell in the waters, 

 flourished upon the globe long ages before the chalk was 

 deposited. Very few, however, if any, of these ancient forms 

 of animal life were identical with those which now live. 



