HAMILTON ISCIENTIFIC ASSOCIATION. 19 



feet, the three-toed or five-toed bird-Hke imprints of which are 

 numerous in some beds of sandstone. The earh'est known croco- 

 diles have been found in the Triassicrocks. But the most import- 

 ant advance was the appearance of mammalian life. The represen- 

 tatives at this time, however, were small creatures. 



Jurassic or Oolitic : Sandstone, shales and limestone alternate 

 more frequently and are more local in their extent, indicating 

 greater changes in process of deposition and more frequent alterna- 

 tions of sea and land. Flora is the same as before. Among the 

 conifers are the remote ancestors of our pines and firs. Remains 

 of numerous cycads have been found in Spitzbergen, showing that 

 the climate of the Arctic regions must have been at that time sub- 

 tropical. Animal life much more varied both in land and sea than 

 during previous ages. A characteristic feature was a profusion of 

 corals — no longer the Rugose ones of the Palaeozoic seas, but the 

 true reef-building coral. 



Crinoids still abundant, but old types disappear, and form be- 

 comes like those found in seas at the present day. Sea-urchins 

 swarmed on the sea floor. Trilobites entirely disappear. Abun- 

 dant ten-footed crustaceans — the ancestors of our lobsters, shrimps 

 cray-fish and crabs — make their appearance. Certain beds contain 

 numerous remains of insects — dragon-fly, May-fly, grasshopper and 

 cockroach. The wing of a butterfly was also found. Fishes 

 abounded — ganoids and various tribes of sharks. Reptiles were so 

 remarkably developed that this has been called " the age of rep- 

 tiles." Some forms haunted the sea, some frequented the rivers, 

 some lived on land and some flew through the air. The descend- 

 ants of these are our crocodile, alligator and turtle. But most 

 types are long extinct. Of these sea lizards, the icthyosaurus was 

 24 feet long and resembled a whale in shape and bulk. Pleisosaurus 

 differed from previous ones by having shorter tail, longer neck, 

 smaller head, larger paddles, and teeth in distinct sockets. It 

 probably haunted lagodns, fivers and shallow seas. Its long swan- 

 like neck eriabled it to lie at the bottom of watet and raise its head 

 to the sui'face to breathej Of When at the surface to s&nd down its 

 fQWerful Jawrt iud eatch itf* prey at the bottom, f^terssaurs, Qt 



