154 NEOZOIC TIME. [CHAP. IX. 



the Coal-measures into the sandstones, limestones, and older 

 rocks beneath ; a slight elevation would quicken this process 

 of erosion, and the natural result would be that the rivers 

 would carry less mud, but more sand in suspension, and 

 more calcareous matter in solution. In the combined effect 

 of the two causes above indicated we seem to have a com- 

 plete explanation of the rapid change from the physical 

 conditions of the Lias to those of the Oolitic sea. 



In the epoch of the Great Oolite there appears to have 

 been a certain amount of subsidence in the southern dis- 

 tricts, for we know that this stage overlapped the Lias in 

 the latitude of London (see p. 140), and also in the north- 

 east of France ; this overlap may, however, have been partly 

 due to erosion of the coast by the waves ; there is no proof 

 that the northern area was affected by the subsidence, and 

 it was evidently insufficient to cause any material altera- 

 tion of the geographical conditions. 



Throughout this Oolitic epoch the clear water and warm 

 temperature of the southern sea were favourable to the 

 growth of coral-reefs, and it is well known that the Oolitic 

 limestones are to a large extent formed from the materials 

 derived from the waste of such reefs and from the shells of 

 the marine creatures which swarmed in their neighbour- 

 hood. As in similar situations at the present time, Echi- 

 noderms, Brachiopoda, Pelecypoda, and Gasteropoda were 

 especially abundant. 



The fauna and flora of the land were in keeping with 

 those of the sea. Terns, Cycads, and Equisetums abounded 

 on the borders of the rivers, and were mingled with Coni- 

 ferous trees on the higher slopes ; huge Dinosaurian Rep- 

 tiles, that walked or hopped on their hind legs like kanga- 

 roos, and small insectivorous Marsupials were the chief 

 vertebrate inhabitants of the dry land, but Crocodiles 

 swarmed in the rivers, and bat-like Pterodactyles flitted 

 through the air. 



