Scrope — On the Internal Fluidity of the Globe. 539 



more j^radual elevation like a creep, or, more frequently perhaps, 

 slow subsidence. The cause of these local changes being the trans- 

 mission of heat by conduction from one part to another, — " the ten- 

 dency of heat to seek an equilibrium being as much a law of nature 

 as of water to seek a level" (p. 267, Volcanos) ; and the disturbance 

 of its equilibrium arising not merely from the outward radiation of 

 heat into space from the earth's surface, but also probably (as sug- 

 gested by me in 1825,^ and subsequently by Mr. Babbage^) from the 

 pressure and accumulation of vast thicknesses of nonconducting de- 

 posits in the depths of seas and oceans. 



I am gratified to find that these views as to the nature and modus 

 operandi of the subterranean agents of change in the earth's crust, 

 which I published more than forty years back, are now becoming 

 recognized as true by many — perhaps the majority of geologists — 

 more especially as respects the large part played in these movements 

 by the water contained in the interior heated matter which eventually 

 on its superficial cooling forms the substance of all hypogene rocks. 

 For entertaining this view, I was at that early period subjected to 

 much ridicule, and my arguments generally disregarded. There re- 

 main, I think, but two other portions of the theory advanced by me, 

 at the early period I have mentioned above, of considerable importance, 

 to which the assent of geologists has not as yet been given, namely, the 

 suggestions — 1st. That when the heated and liquefied mineral matter 

 has forced its way upwards through some fissure into open air, it has 

 rarely been in a state of true fusion, but generally semi- crystalline ; 

 and that it has cooled and hardened outwardly on exposure, not so 

 much as melted metal cools and hardens, but rather by the rapid 

 escape, through pores or in ascending bubbles, of its interstitial water, 

 flashing into steam as the internal pressure diminished (p. 115, 

 Volcanos). 2nd. That the internal diiferential movements of the 

 subterranean mineral matter, while under enormous irregular pres- 

 sures, and changing at times from a solid to a fluid state, and pro- 

 bably back again to crystalline solidity, through every intervening 

 phase of viscosit}'-, must of necessity have frequently arranged and 

 re-arranged the component crystalline or semi-crystalline minerals — 

 sometimes in irregular composition like that of granite, diorite or 

 trachyte — sometimes in laminar or schistose bands like gneiss, mica- 

 schist, and other metamorphic crystallines.^ I hope the time is not 

 distant when these opinions likewise will obtain the assent of 

 geologists. 



Fairlawn, Cobham, 

 November 15, 1868. 



1 Volcanos, ecL 1825, p. 30, and ed. 1862, p. 271. 



2 Geol. Proceed, vol. ii. p 72. 



3 See p. 283-290, above cited vol., and of the Geologist, vol. i. p. 361. 



[See also Letter by Mr. J. Clifton Ward, on the " Internal Fluidity of the Earth," 

 p. 581 of this present number. — Edit.] 



