380 Correspondence. 



recent eartliqtiakes, Mr. Jukes will not of course deny. All geolo- 

 gists, indeed, recognise as a natural law the tendency of all the ex- 

 ternal denuding forces to reduce the surface of the earth to one 

 uniform level, so that hut for the ojoposing agency of the subterra- 

 nean forces no dry land could long exist. It seems, therefore, like a 

 paradox to deny to the latter power any "direct" or considerable 

 share in the external configuration of the earth. 



But there is something more than this to be said. Mr, Jukes, as 

 I before remarked, makes the large admission that all volcanic hills 

 and moimtains are superficial protuberances " directly" produced by 

 internal force. Now, on examination of any map of the globe 

 showing the position of the laiown volcanos and volcanic formations, 

 it will be seen that they are for the most part arranged in linear 

 bands bearing a remarkable parallelism to the nearest non-volcanic 

 mountain ranges. Must there not be some common cause for this 

 remarkable correspondence of direction ? May we not presume that 

 Mobile the volcanic mountain ranges have risen by means of the 

 eruption through linear fractures of the earth's crust of subterranean 

 matter in a liquified or gaseous condition, the non-volcanic moun- 

 tains have been contemporaneously rising through parallel fractures, 

 in consequence of the upward pressure of subterranean matter, which, 

 not being able to find an issue in a liquified or gaseous form, has 

 forced itself, in a more or less solid or pasty state, into and through 

 the overlying rocks, carrying them up with it, or shouldering them 

 off on either side,- — and thus bringing up to or near the surface 

 those bulky crystalline masses and corrugated metamorphic strata 

 of which the axial portions of such mountain ranges are so often 

 seen to consist ? It seems certain, for example, that the Alps and 

 Pyrenees Avere risiag by degrees from below the sea while the inter- 

 mediate granitic plateau of Central France remained stationary in 

 level, but gave birth to a series of volcanic eruptions which deluged 

 its surface, and that of the lacustrine strata, that filled its hollows 

 with lava-beds. A similar series of eruj)tions were about the same 

 time taking place along a band of country north of the Alps and 

 nearly parallel to their main direction, reaching from the Ehine 

 through Central Germany to Hungary. If we are ever to acquire 

 any definite notion of the changes that have taken place in the crust 

 of the globe, and the causes of its varying external configuration and 

 internal structure, we must not lose sight of considerations such as 

 these, or undervalue the internal forces which have unquestionably 

 contributed quite as much, if not more,~than external denuding agen- 

 cies to produce the results in question. 



It was simply to remind Professor Jukes and geologists in general 

 of this, and not to go more deeply into a subject of such importance, 

 that I ventured to challenge his apparent negation of the " internal 

 forces" of the globe as one of the "direct" causes of its superficial 

 configuration. 



G. POULETT SCEOPE. 

 Castle Combe, Chippenham, July \Oth, 1866, 



