232 THE STORY OF THE EARTH AND MAN. 



lowed. Those of the land might have retreated to 

 the tracts still remaining out of water, and when the 

 dry land again appeared in the earlier Tertiary, they 

 might again have replenished the earth, and we might 

 thus have truly been living in the Reptilian age up to 

 this day. But it was not so. The old world again 

 perished, and the dawn of the Tertiary shows to us at 

 once the dynasties of the Mammalian age, which wap 

 to culminate in the introduction of man. With the 

 great Cretaceous subsidence the curtain falls upon the 

 age of reptiles, and when it rises again, after the vast 

 interval occupied in the deposition of the greensand 

 and chalk, the scene has entirely changed. There 

 are new mountains and new plains, forests of different 

 type, and animals such as no previous age had 

 seen. 



How strange and inexplicable is this perishing of 

 types in the geological ages ! Some we could well 

 spare. We would not wish to have our coasts in- 

 fested by terrible sea saurians, or our forests by car- 

 nivorous Dinosaurs. Yet why should these tyrants 

 of creation so utterly disappear without waiting for 

 us to make war on them ? Other types we mourn. 

 How glorious would the hundreds of species of Am- 

 monites have shone in the cases of our museums, had 

 they still lived ! What images of beauty would they 

 have afforded to the poets who have made so much of 

 the comparatively humble Nautilus ! How perfectly, 

 too, were they furnished with all those mechanical 

 appliances for their ocean life, which are bestowed 



