30 ON A PIECE OF CHALK i 



I must ask you to believe that there is no less 

 conclusive proof that a still more prolonged sue- 

 cession 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 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 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. Certainly 

 not one of the higher animals was of the same 

 species as any of those now in existence. The 

 beasts of the field, in the days before the chalk, 

 were not our beasts of the field, nor the fowls of 

 the air such as those which the eye of men has 

 seen flying, unless his antiquity dates infinitely 

 further back than we at present surmise. If we 

 could be carried back into those times, we should 

 be as one suddenly set down in Australia before it 

 was colonized. We should see mammals, birds, 

 reptiles, fishes, insects, snails, and the like, clearly 



