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XXXVII. Reply to Dr. Boase's " Ilemarks on Mr. Hopkins's 

 ' Researches in Physical Geologi/" iji the Number for July. 

 Bi/ W.Hopkins, Esci., M.A.^'F.G.S.,qfSt. Peter' s College, 

 Cambridge. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



T BEG to reply through the medium of your Journal to 

 some remarks by Dr. Boase, contained in your last Num- 

 ber [for July], p. 4, on my memoir on Physical Geology, and 

 to add some additional facts which I have recently had an 

 opportunity of observing. 



Dr. Boase appears in the first place to object to the hypo 

 thesis on which the whole of my investigations are founded, 

 that of the simultaneous action of an elevatory force on the 

 exterior crust of the globe throughout regions of considerable 

 extent, because he conceives that extensive dislocations pro- 

 duced by such a force would probably be attended with enor- 

 mous convulsions proportioned to the extent of the rupture. 

 This objection rests entirely on an assumption as to the in- 

 tensity of the elevatory force. Dr. Boase has not given any 

 reason for supposing that explosion must probably accompany 

 dislocation, and without some such reason it is certain that 

 we have no right to make the assumption. It is obvious, in 

 fact, that we can have no means whatever of judging of the 

 intensity of the elevatory force except by the effect produced 

 by it. For anything we can know of its nature independently 

 of inference from observed phaenomena, it might be insuffi- 

 cient to produce an earthquake or adequate to produce an 

 almost universal volcano. It may be observed, however, that 

 the extent of simultaneous dislocation would do more than 

 anything else to counteract the explosive tendency of an ex- 

 pansive fluid, because the more extensive the dislocations the 

 more rapidly would the force of expansion be diminished, and 

 the more equable would be the effect on the whole mass. If, 

 on the contrary, a small portion only of the mass should give 

 way, the expansive force would be but little diminished, and 

 its continued action on the yielding part would unquestionably 

 produce much more violent eftects on that part than if the 

 mass had yielded generally. 



Dr. Boase has rested his objection partly also on the notion, 

 that according to my views the fissures must necessarily begin 

 at the under or lovocst side of the elevated mass. He will 

 find it carefully stated, however, in n)y memoir, that they " will 



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