212 THE WORLD OF LIFE CHAP. 



they occupied almost as important a place in nature 

 as do the birds now. Yet not one of the varied forms 

 either of the terrestrial Dinosaurs, the aerial Pterodactyls, 

 or the aquatic Sauropterygia and Ichthyopterygia all 

 abounding down to Cretaceous times ever survived the 

 chasm that intervened between the latest Secondary and 

 the earliest Tertiary deposits yet discovered. This is 

 perhaps the most striking of all the great geological 

 mysteries. 



One more point may here be noticed. The early 

 small-sized Pterodactyls arose just when highly organised 

 winged insects began to appear, such as dragon-flies and 

 locusts, soon followed by wasps, butterflies, and two-winged 

 flies in Middle Jurassic times ; from which period all orders 

 of insects were no doubt present in ever-increasing numbers 

 and variety. 



It is interesting to note further, that at the very same 

 epoch in which we find this great increase of insect life there 

 appeared the first true flowering plants allied to the Cycads, 

 with which they were till quite recently confounded. These 

 also must have rapidly developed into a great variety of 

 forms, since in the later Cretaceous formation in many parts 

 of the world true flowering plants, allied to our magnolias, 

 laurels, maples, oaks, walnuts, and proteaceous plants, appear 

 in great abundance. These seem to have originated and 

 developed very rapidly, since in the earliest deposits of the 

 same formation none of them occur. 



Mesozoic Mammalia 



There is perhaps nothing more remarkable in the whole 

 geological record than the fact of the existence of true 

 mammals contemporaneous with the highly diversified and 

 abundant reptile life throughout the period of their greatest 

 development from the Trias to the Cretaceous. They were 

 first discovered nearly a century ago in the Stonesfield Slate 

 at the base of the Great Oolite in Oxfordshire, and were 

 described under the names Amphitherium and Phascolo- 

 therium (Fig. 67). About forty years later a considerable 

 number of similar remains small mammalian jaws with 



