ix.] ON A PIECE OF CHALK. 197 



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 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 incessant, 

 changes. There has been no grand catastrophe — no 

 destroyer has swept away the forms of life of one 

 period, and replaced them by a totally new creation ; 

 but one species has vanished and another has taken 

 its place ; creatures of one type of structure have 

 diminished, those of another have increased, as time 

 has passed on. And thus, while the differences between 

 the living creatures of the time before the chalk and 

 those of the present day appear startling, if placed 

 side by side, we are led from one to the other by the 

 most gradual progress, if we follow the course of Nature 

 through the whole series of those relics of her operations 

 which she has left behind. 



And it is by the population of the chalk sea that the 

 ancient and the modern inhabitants of the world are 

 most completely connected. The groups which are 

 dying out flourish, side by side, with the groups which 

 are now the dominant forms of life. 



