MODIFIED by COMPRESSION 169 



upwards. That they have been really fo propelled, from a 

 great internal mafs of matter, in liquid fufion, feems to admit 

 of no doubt, to whatever caufe we afcribe the heat of volcanoes. 

 It is no lefs obvious, that the temperature of that liquid muft 

 be of far greater intensity than the lavas, flowing from it, can re-* 

 tain when they reach the furface. Independently of any actual 

 eruption, the body of heat contained in this vaft mafs of liquid, 

 muft difFufe itfelf through the furrounding fubftances, the in- 

 tenfity of the heat being diminifhed by flow gradations, in pro- 

 portion to the diftance to which it penetrates. When, by means 

 of this progreffive diffulion, the heat has reached an afTemblage 

 of loofe marine depolltes, fubject to the preffure of a great fu- 

 perincumbent weight, the whole muft be agglutinated into a 

 mafs, the folidity of which will vary with the chemical com- 

 pofition of the fubftance, and with the degree of heat to which 

 each particular fpot has thus been expofed. At the fame time, 

 analogy leads us to fuppofe, that this deep and exteniive heat 

 muft be fubject to viciflitudes and intermiflions, like the exter- 

 nal phenomena of volcanoes. We have endeavoured to explain 

 fome of thefe irregularities, and a fimilar reafoning may be ex- 

 tended to the prefent cafe. Having fhewn, that fmall in- 

 ternal ftreams of lava tend fucceflively to pervade every weak 

 part of a volcanic mountain, we are led to conceive, that the 

 great maffes of heated matter juft mentioned, will be fucceflive- 

 ly directed to different parts of the earth ; fo that every loofe 

 afTemblage of matter, lying in a fubmarine and fubterranean 

 fituation, will, in its turn, be affected by the indurating caufe j 

 and the influence of internal volcanic heat will thus be cir- 

 cumfcribed within no limits but thofe of the globe itfelf. 



A series of undoubted facts prove, that all our ftrata once 

 lay in a fituation fimilar in all refpects to that in which the 

 marine depofites juft mentioned have been fuppofed to lie. 



The inhabitant of an unbroken plain, or of a country form- 

 ed of horizontal ftrata, whofe obfervations have been confi- 



Vol.VI.^P.I. Y ned 



