ANt) ANALOGIES, OF ROCKS. 217 



of animals so far exceeding these in bulk and in the 

 relative quantity of their calcareous produce, should 

 have generated all the calcareous strata in the secon- 

 dary series. 



It is not necessary here to ask whence the calcareous 

 matter has been derived, or to suppose that it is an 

 animal product. That difficulty is at present, unques- 

 tionably, insurmountable; but, in this case, it is of no 

 moment. It can form no objection to the power of 

 oysters or pectines in producing, by their own energies, 

 a bed of limestone; because the fact, however inex- 

 plicable, is rendered unquestionable by the generation 

 of coral from sea water. That very extensive beds of 

 calcareous matter may be produced by animals, and 

 from their remains, is also incontestably proved by the 

 oolithe limestones, and by those deposits of shell marl 

 so often found in fresh water lakes. In many such 

 cases in the Highlands of Scotland, it can easily be 

 demonstrated that this is their sole origin; because we 

 can trace the courses of the streams by which the 

 lakes have been fed, and ascertain that they could not 

 have carried down calcareous matter; their origin and 

 progress lying among siliceous strata. 



It must be admitted indeed, that whatever calcareous 

 beds may be at this moment preparing at the bottom 

 of the ocean, the probable germs of future strata, they 

 will be formed, like the shales and sandstones, from 

 the ruins of the present calcareous secondary rocks; 

 and that the operations of shell fish will constitute 

 only a part of the causes of their production. Nor 

 need it be denied that such has been the case to 

 a certain degree in former times: but that the as- 

 sistance afforded by the ruins of primary calcareous 

 rocks has been very trifling, will appear evident from 



