228 THE WORLD OF LIFE 



occupied almost as important a place in nature as do tlie birds 

 now. Yet not one of the varied forms either of the terrestrial 

 Dinosaurs, the aerial Pterodactyls, or the aquatic Sauroptery- 

 gia and Ichthyopterygia — all abounding down to Cretaceous 

 times — ever survived the chasm that intervened between the 

 latest Secondary and the earliest Tertiary deposits yet discov- 

 ered. This is perhaps the most striking of all the great geolog- 

 ical 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 ap- 

 peared 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 mam- 

 mals 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 Phascolotherium (Fig. 67). About 

 forty years later a considerable number of similar remains 



