AGE OF FORMATION 153 



origin to upheaval ; they were formed as the chalk of the 

 deep sea was raised to form the dry land of the Chiltern 

 hills and other regions. If, then, the joints have deter- 

 mined the deposition of the flint, as they seem to have 

 done, then the flint must be subsequent to the joints, 

 and subsequent, consequently, to the upheaval. This is in 

 harmony with the fact that flints have never yet been 



FIG. 44. Banding produced by the spread 

 of Oil in Writing-paper. 



dredged from the ooze of the existing sea, and it is con- 

 sistent with the discovery of hollow casts of sponge 

 spicules in the chalk, which must have acquired a 

 considerable degree of consistency before it could pre- 

 serve in such a remarkable state of perfection these 

 perishable cavities. Probably the deposition of the flint 

 about the joints is due to the open cavity, which these 



