XIV. 



GRAINS OF OOLITE. 



395 



of small and very equal size, cohering by their surfaces without 

 intervening cement. 



The Bath oolite contains similar beds of 'fine freestone/ and 



Diagram CXCIII. Magnified sections of grains of oolite, shewing aggregation 

 round an organic nucleus, i . A grain gathered round a finger-joint of a crinoid ; 

 2. round a small spine of Cidaris ; 3. round a minute foraminifer. 



in these it is not uncommon to find the spherules hollow within, 

 so that the stone is very light and very absorbent of water. 



The oolite of Ancaster in Lincolnshire has beds in which the 

 grains are immersed in a matrix of clear calcite, whose glistening 

 faces and cleavage lines are evident on fracture. This crystalline 



Diagram CXOIV. Magnified view of a discoid foraminifer, with a thin accretion 

 of calcareous matter, constituting an oolitic grain. 



network may often be detected in parts of those rocks which are 

 not obviously oolitic, and indeed are somewhat arenaceous. 



