THEORY OF THE EARTH. 449 



form one of the greatest blanks in a general Theory, 

 geology has not even a rational conjecture. I have 

 already collected and analysed the essential facts on 

 which it must be founded, as far as these are known ; 

 this at least had never been done : but I must leave 

 the rest to posterity. That the theory of certain 

 springs is another blank, it is sufficient to note. 



I have shown that the unstratified rocks are all, 

 equally, of igneous origin, carrying on the chain back- 

 wards from the volcanic ones; that the mineral cha- 

 racters of all the species are analogous, and pass into 

 each other ; that a mineral character in any one has 

 no necessary dependence on its period of production ; 

 and that all have originated in the interior of the 

 globe, with some local exceptions of earths fused in 

 situ. That, short of such absolute fusion and loss of 

 form, antient strata of a simple character have become 

 what our primary ones now are : while those which 

 have been most exposed to heat have undergone the 

 greatest changes, as, on the other hand, those which 

 have felt less of this influence have suffered the least. 

 But also, that, in all cases, where they contain inde- 

 pendent crystallized minerals, these have been pro- 

 duced by heat ; possibly, often short of effecting their 

 absolute fusion. And that all this is confirmed by lo- 

 cal facts, which also give the analogous theory of cer- 

 tain partial rocks, such as jasper, chert, and siliceous 

 schist. Whence also, especially, from the local fusion 

 of conchiferous limestone into marble, are drawn the 

 inferences respecting the organic origin of the earlier 

 limestones. And thus, referring to the several chap- 

 ters for fuller details, the theory of each rock is as 

 follows ; as far as they are not altered by water. 



All the granites, porphyries, and traps, with little 

 exception,, were fused and effused fluids, and their va- 



VOL. n. G G 



