Composition, ^'^^d Analogies of Rocks. 20S 



It must be admitted, indeed, that whatever calcareous beds 

 may he at this moment preparing nt the bottom of the ocean, as 

 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 only 

 form 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 assistance afforded by the ruins of primary 

 calcareous rocks has been very trifling, will appear evident from 

 a mere arithmetical comparison, which can scarcely deceive. 



Every thing proves that the present secondary strata are the 

 produce of more ancient rocks ; and these must have been the 

 continuations of those which are now the primary, as we have no 

 reason to imagine that there has been a distinct series wliich has 

 entirely vanished. The proportions of the different materials in 

 the produce, ought, therefore, to bear a certain relation to those 

 in the original repositories ; or, if there was a difference, it should 

 be expected to be in favour of the most yielding materials, schist 

 and -limestone. But if we examine the quantity of limestone in 

 the primary strata, it will be found very small. What the exact 

 proportion of limestone to the other rocks may be throughout the 

 world is not known ; but, in Scotland and England, it certainly 

 does not amount to a thousandth part of the whole. But among 

 the secondary strata of England, the limestones bear a far larger 

 proportion to the siliceous and argillaceous rocks. If we were to 

 assume only the ratio of one hundredth, it would answer the pur- 

 poses of the present argument; and there is nothing unreasonable 

 in referring the origin of the British secondary strata to the 

 British primary rocks. In the same manner, and with the same 

 consequences, we may refer the origin of the Apennines to the 

 Alps. This, however, is a matter of indifference, as the general 

 fact, taking the whole world, is indisputable. 



Thus, it may fairly be inferred, that while the siliceous and 

 argillaceous secondary strata have been formed from the ruins of 

 more ancient rocks, <i large part, at least, of the calcareous, is the 

 produce of animals. ITius also, it must appear, that from the 



