102 MICROSCOPICAL OBJECTS FOUND 



on a moor near the same place. The slightest 

 communication between them would make them 

 both of an inky blackness. They apparently derive 

 their mineral contents from different strata, which 

 are being slowly, but surely, robbed of their 

 mineral contents ; and thus Tertiary deposits may- 

 have been deprived of all their calcareous organ- 

 isms by a slow and long-continued process, which 

 has left the insoluble siliceous structures alone 

 undestroyed. 



Tt may be objected, that no such explanation 

 as this will apply to those extensive Limestone 

 rocks already alluded to, where the calcareous 

 matter still remains, though with an obviously 

 altered structure. In such cases the lime has 

 not been removed. This does not materially 

 affect the argument. It only shews that a double 

 process of interstitial solution and re-deposition 

 or crystallization has been going on at the same 

 time. However difficult to explain, the fact may 

 be considered certain, as it is capable of the 

 most satisfactory illustration. It is proved by 

 the spines and plates of Echinodermata, found 

 in the Oolitic strata, where, though the atoms of 

 lime still retain the exact form, and exhibit the 

 beautiful reticular structure of the living organism, 



