Formation of Flints in Chalk. 423 



Again ; the absence in chalk flints of that arrangement of the 

 silex in concentric or parallel plates, which geodes of an agate-like 

 origin would possess, adds weight to the arguments that have been 

 offered against the existence of any identity in the manner of for- 

 mation of agates and chalk flints. 



S h 2 



