430 SKETCH TOWARDS A 



account for every new modification which the Earth 

 has undergone ; with the preceding doubts, only. 



If, thus far, the theory seems perfect, there is an 

 involved difficulty which geology cannot yet solve, 

 and probably never will; since I cannot foresee whence 

 evidence can possibly come. The expansions, or 

 Revolutions, in the first, solid condition, or third form 

 of the Earth, ought to have been numerous and long 

 continued, on general principles; it was a durable 

 state of commotion, as of solidification. In the sub- 

 sequent ones, the apparent effects are those of a single 

 action of the same nature. This is all that we see: 

 yet if allowed to infer from the present nature of vol- 

 canic action, it is more probable that each such con- 

 dition of revolution was tedious, and the disturbing 

 motions successive. 



Further than this, I can say nothing: but I must 

 re-urge that difficulty which forms an additional blank 

 in a true Theory of the Earth ; while, as to this also, 

 I can foresee no chance of evidence. Was the whole 

 Earth, or only a portion of it, involved, in all those 

 cases which I have here marked as successive condi- 

 tions? This is a most important question: for the 

 blanks which it leaves unexplained, are enormous; 

 inasmuch as it includes the weighty fact, whether 

 the revolutions concerned in the coal and in the lig- 

 nites were limited, or not, to one portion of the globe, 

 as the posterior one which acted on Italy seems to have 

 been much Jess than universal. On this, I am power- 

 less: and can only remark, that every other one ap- 

 pears to have been universal, from the presumed ex- 

 istence of similar strata all over the globe, as far up 

 at least as the red marl, itself a portion of that state 

 of the earth which is nearly the latest. 



But there is one important fact connected with these 



