550 



a strictly theoretical explanation of the effects of heat on newly de- 

 posited strata ; and this, simply because the fact of new strata ha- 

 ving been deposited, the conditions of the equilibrium of temperature 

 become altered, and they draw the heat to them, or rather retain it 

 in them in its transit outwards; the supply from the centre being 

 supposed inexhaustible, and its temperature of course invariable. 



As the greatest transfer of material to the bottom of the ocean is 

 produced on the coast line by the action of the sea, while the quan- 

 tity carried down by rivers from the surface of continents is compa- 

 ratively trifling ; hence therefore the greatest local accumulation of 

 pressure is in the central area of deep seas, but the greatest local 

 relief takes place along the abraded coast lines: here, therefore, 

 according to this view should occur the chief volcanic vents. 



In this view the effects of the removal of matter from above to 

 below the sea, are, 1st. It produces a mechanical subversion of the 

 equilibrium of pressure. 2nd. It also, and by a different process, 

 produces a subversion of the equilibrium of temperature. The last 

 is the most important. It must be an exceedingly slow process, and 

 will depend, 1st. On the depth of matter deposited ; 2nd. On the 

 quantity of water retained by it under the great pressure ; 3rd. On 

 the tenacity of the incumbent mass — whether the influx of caloric 

 from below, which must take place, acting on that water, shall either 

 heave up the whole mass as a continent ; or shall crack it and escape 

 as a submarine volcano ; or shall be suppressed until the main weight 

 of the continually accumulating mass breaks its lateral supports at or 

 near the coast lines, and opens there a chain of volcanos. 



Thus the circuit is kept up — the primum mobile is the degrading 

 power of the sea and rains (both originating in the sun's action) 

 above, and the inexhaustible supply of heat from the enormous re- 

 sources below, always escaping at the surface, unless when repressed 

 by an addition of fresh clothing at any particular part. In this view 

 of the subject the tendency is outwards. Every continent deposited 

 has a propensity to rise again, and the destructive principle is con- 

 tinually counterbalanced b)'^ a reorganizing principle from beneath. 

 Nay, it may go further ; there may be such a tendency in the globe 

 to swell into froth at its surface, as may maintain its dimensions in 

 spite of its expense of heat, and thus preserve the uniformity of its 

 rotation on its axis. 



Extract of a letter from Sir John F. W. Herschell to R. I. Mur- 

 ' chison, Esq., in explanation of the former, to C. Lyell, Esq., dated 

 Fredhausen, 15th November, 1836, was afterwards read. 



In this letter the author recapitulates the views given in the fore- 

 going abstract, stating that his views are not so much a theory as a 

 pursuing into its consequences, according to admitted laws, of the 

 hypothesis of a high central temperature; and his object to get a 

 geological primum mobile in the nature of a vera causa, and to 

 trace its workings in a distinct and intelligible manner, so that in 

 future, instead of saying as heretofore, " Let heat from below invade 

 newly deposited strata, then they will expand, melt,"' &c., we shall 



