414 SKETCH TOWARDS A 



tute limestones at present, and have produced them, 

 at distant and different periods, in immense masses; 

 nor, for those of present times, is there any other origin 

 than animal chemistry; except, that limestones must 

 be reproduced from limestones, as sandstones are from 

 sandstones: though it is still inferred that such was 

 the first origin of the whole; which diminish in quan- 

 tity as we retrocede in the order of the strata, or the 

 age of the globe. These strata thus furnish that cri- 

 terion for the number of animals at any period of the 

 Earth, which is, more obviously but less sufficiently, 

 proved by their actual preservation in such strata. 



The solid parts of vegetables now produce peat, 

 which passes, under greater antiquity, to lignite, and 

 lastly to coal: for which, as in the former case, no 

 other origin can be assigned: while, in a similar way, 

 the actual fragments of plants preserved in these strata, 

 further prove that such is their origin. It is less safely 

 inferred, however, that there is no other origin for 

 carbon than vegetable chemistry. 



The principal strata were formed under the sea, and 

 at different periods of repose; being also originally 

 in a horizontal position, or nearly so. And any set 

 of strata, maintaining a parallel order, has been formed 

 in one such period. But the first strata must have 

 been produced from the waste of igneous rocks; since 

 this is a necessary inference from the very nature of 

 stratification. Thus does a stratum containing a frag- 

 ment of a former one, prove an anterior set belonging 

 to a previous period; as that fragment would prove 

 one still anterior, should it contain the materials of a 

 stratified rock, under whatever form. Whence is 

 established the former existence of sets of strata and 

 periods of repose in the earth, of which we have no 

 other evidence. 



The formation and protrusion of igneous rocks have 



