On a Piece of Chalk 97 



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 5 

 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 10 

 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 15 

 the like, clearly recognizable 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, 20 

 changes. There has been no grand catastrophe no de- 

 stroyer 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 25 

 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 30 

 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 



