THE 



GEOLOGICAL MAGAZINE. 



No. LVIII.— APRIL, 1869. 



I. — On the Supposed Inteenal Fluidity op the Earth. 

 By G. PouLETT ScROPE, Esq., F.R.S., F.G.S. 



[Second Notice]. 



IN Hs recent volume on " Vesuvius," Professor Phillips has added 

 the weight of his great authority to the popular opinion as to 

 the complete internal fluidity of the globe. It may not, therefore, 

 be out of place to examine very shortly the chief argument which 

 appears to have led him to adopt this view, and to discredit that ad- 

 vocated in my paper in your December number, namely, that " pres- 

 sure, by raising the temperature of fusion" in the matter immediately 

 beneath the exterior crust, probably prevents its liquefaction ; in 

 other words, maintains it in a solid state, except where some upheaval 

 of the surface rocks, or the production of some deeply penetrating 

 fissure, has by a sudden reduction of pressure admitted of its local 

 liquefaction. 



The Professor opposes to this view the consideration that, " ac- 

 cording to all analogy, pressure must rise (downwards) in a higher 

 ratio than temperature in order to prevent solidification ; and as both 

 temperature and pressure must rise in arithmetical progression (at 

 such depths as we are now considering) it is most probable that 

 liquefaction can only be prevented in a slight degree by pressure ; 

 very possibly it is not prevented at all." (Vesuvius, p. 329.) Now 

 it is evident that this argument rests on the assumption that the 

 pressure to which any interior liquid mass is subjected, consists of 

 the force of gravity alone, and (as I urged in my last paper) ignores 

 the increased pressure arising necessarily " from the tendency to ex- 

 pansion of every part caused by its extreme heat, whether in a solid, 

 liquid, or gaseous state — more particularly if, as there is reason to 

 believe, the subterranean matter is intimately permeated with water, 

 itself occasionally solidified by pressure, but yet retaining its intense 

 expansibility." Surely this vast elastic force, resisted in its action bj^ 

 the weight, cohesion, and perhaps increasing contraction of the solid 

 crust above, may well be supposed to augment the pressure on every 

 part so far as to turn the balance in favour of solidification. 



The ideas of those who advocate the fluidity of the interior of the 



VOL. VI.— NO. LVIII. 10 



