ON A PIECE OF CHALK 67 



I must ask you to believe that there is no less con- 

 clusive proof that a still more prolonged succession of 

 similar changes occurred, before the chalk was de- 

 posited. 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 iden- 

 tical 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 in- 

 finitely 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 recognisable 

 as such, and yet not one of them would be just the 

 same as those with which we are familiar, and many 

 would be extremely different. 



From that time to the present, the population of 

 the world has undergone slow and gradual, but inces- 

 sant changes. There has been no grand catastrophe 



