182 GEOLOGICAL HISTORY. 



tinuing or renewed, we find the sediments changed ; chalk re- 

 places the oolites perhaps because the ocean was now opened 

 to new sources, and closed against those which had been long in 

 action. The sandstones and shales of the oolitic series in York- 

 shire came by inundations from the north ; the oolitic element 

 was in great degree the effect of lime separated from the sea by 

 the functions of animal life. The chalk in like manner contains 

 evidence of the effect of such vital powers, but not so abundantly 

 in Yorkshire as in the southern counties. Its numerous bands 

 of flint nodules are in a lower part of the mass than in other 

 parts of England. Sponges are not usually found in these 

 nodules, but lie in the chalk itself (the upper part), and are re- 

 markably distinct in appearance and character, because their 

 tissue is siliceous*. With them lie many Marsupites, Apiocri- 

 nites, Echinida, and Belemnites ; other Cephalopoda and some 

 Fishes do occur, but they are not frequent. 



Organic remains. These are purely marine, and wholly of 

 animal origin. The groups at present discovered are fewer in 

 Yorkshire than in the south of England ; Dimyaria, Gasteropoda, 

 and Reptiles being as yet unknown here. The Reptile from 

 which the group is named (Mosasaurus) occurs in the south of 

 England. The most numerous of all are the Amorphozoa, 

 Crinoidea, Echinida, and Belemnites. 



Amorphozoa. Monomyaria. 



Foraminifera. Brachiopoda. 



Polyparia. Annulosa. 



Asterida. Cephalopoda. 



Crinoidea. Fishes. 

 Echinida. 



PAL^EOTHERIAN PERIOD. No monuments of this, the Eocene 

 period of Lyell, occur in Yorkshire, nor is any special fact ob- 

 served from which the state of things here at that time may be 

 correctly inferred. The absence from Yorkshire of the deposits 



* Mr. Charlesworth has availed himself of this property, and by immer- 

 sion in dilute acid has obtained for the Yorkshire Museum beautiful speci- 

 mens. 



