314- ON THE IGNEOUS METAMORPHOSIS [Ch. XIV. 



the worth of every hypothesis which has been from time to 

 time engrafted on the original Huttonian theory : but it 

 seems to us, that such examinations, if conducted with can- 

 dour and caution, may be of utility, by leading to more ex- 

 tended researches. In this case, such good results may be 

 expected ; for not only farther geological scrutiny will be sug- 

 gested, but the astronomer, meteorologist, and chemist, must 

 also be applied to for assistance. 



If our planet were originally in a total state of igneous 

 fusion, its present condition shows that it has been cooled to 

 such a considerable extent, that the general temperature of 

 its surface is not now influenced by this internal fire, but 

 depends on another and remoter cause ; and what has taken 

 place during the countless ages required for the production 

 of the aqueous deposits, may be presumed to be still in 

 operation. We can form some idea of the successive changes 

 which might arise during the secular refrigeration of a melted 

 mass, and we may offer plausible explanations of these changes 

 on the known principles by .which matter is governed under 

 similar circumstances : but on what analogies can we picture 

 to our imaginations a central fire, not only maintaining its 

 existence, by some unknown supplies, but even extending its 

 dominion, so as to fuse the rocks on which the oldest strata 

 were deposited, and to bring the latter into a state of intense 

 ignition over a considerable portion of the globe, and within 

 a comparatively insignificant distance from the surface; a 

 distance far less than the total thickness of the secondary and 

 tertiary rocks, many of which must have been formed since 

 the supposed conversion of these strata into the existing 

 primary rocks. We have said that many of the fossiliferous 

 deposits are supposed to have been formed anterior to some 

 of the primary slates, the latter proceeding from the meta- 

 morphic state of the former ; but we might, perhaps, have 

 asserted, on evidence not inferior to that on which this hypo- 

 thesis is founded, that this metamorphosis, if it ever hap- 

 pened, must have preceded the formation of all the secondary 



