CHAP. IX.] JURASSIC PERIOD. 155 



The nearest approach in modern times to such a scene 

 as Britain must have displayed in the Middle Jurassic 

 period is to be found in Australia and its neighbouring 

 islands. There many of the Jurassic types still survive. 

 The indigenous Mammalia are all Marsupials ; the plants 

 include Ferns, Cycads, and Araucarian pines. Coral-reefs 

 fringe the shore, and in the waters are Cestraciont Fish, 

 and many of the same Molluscan genera as are found in 

 the Oolites, viz., Phasianella, Stomatia, Trigonia, Corbis, 

 and Terebratula, with others that have a wider distribution. 

 There are, however, no survivors of the Jurassic Reptiles, 

 or of the Ammonites and Belemnites which swarmed in 

 the older seas. 



Upper Jurassic Time. During this part of the Jurassic 

 period a considerable subsidence took place, and this was 

 followed by a still greater and more continued upheaval, 

 which eventually raised the greater portion of the British 

 area into dry land, and brought the Jurassic period to a, 

 close. 



Once more we have a complete change in the character 

 of the sediment, and as the phenomena exhibited are exactly 

 in reverse order to those of the change from Lias to Oolites, 

 we may assume that they were caused by movements of 

 precisely an opposite kind, and that the epoch of the Oxford 

 Clay was produced by a general and equable subsidence of 

 the whole region from the very south of England to the 

 extreme north of Scotland. 



In this case the sands and sand-rock of the Kellaways 

 Beds are the strata formed at the commencement of the 

 change, and constitute the zone of passage. The sandy 

 nature of the Kellaways rock precludes us from supposing 

 it to have been a deep-water deposit, but its fauna indicates 

 that deep water was not far off, for in these beds a large 

 number of new Ammonites suddenly make their appearance, 

 and most of them continue in the Oxford clav. If further 



