TN THE MUD OF THE LEVANT. 85 



Of the original character of the calcareous rocks 

 below the Chalk, our knowledge is imperfect, owing 

 to the chemical changes they have obviously 

 undergone since their deposition. To a large 

 number of the Oolitic rocks especially, a pisolitic 

 structure has been given which, in all probability, 

 they did not originally possess. This has been 

 illustrated, by Mr. Lyell, in the case of the larger 

 concretions oftheMagnesian Limestone,* and there 

 is little doubt but that somewhat similar changes 

 have been produced in the roestones of Bath and 

 Yorkshire, and the pisolites of Carlsbad. The 

 original state of the calcareous matter to which a 

 pisolitic structure has been subsequently given, 

 is not easily ascertained ; but if it was in the form 

 of minute organisms, such as have been described, 

 owing to their small size, they would be more 

 rapidly destroyed by chemical agents than the 

 larger structures ; what would be sufficient to 

 obliterate the one would produce little visible 

 effect on the other. Hence, in supposing their 

 original existence in these rocks, we are sup- 

 ported by analogy, especially when we remember 

 the close general resemblance between the larger 

 fossils in the Coral and Bath Oolites, and those 



* Elements of Geol. p. 77 . 



