Ch. XXII.] 



EXCAVATION OF VALLEYS. 319 



line of deranged strata in the isles of Wight and Purbeck, as 

 also in the central axis of the Weald, which is inconsistent 

 with the supposition of a great number of separate movements 

 recurring after long intervals of time. But we know that 

 earthquakes are repeated throughout a long series of ages, in 

 the same spots, like volcanic eruptions. The oldest lavas of 

 Etna were poured out many thousand, perhaps myriads, of 

 years, before the newest, and yet they have produced a 

 symmetrical mountain ; and if rivers of melted matter thus 

 continue to flow in the same direction, and towards the same 

 points, for an indefinite lapse of ages, what difficulty is there 

 in conceiving that the subterranean volcanic force, occasioning 

 the rise or fall of certain parts of the earth's crust, may, by 

 reiterated movements, produce the most perfect unity of 

 result ? 



Excavation of Valleys. In our attempt to explain the origin 

 of the existing valleys in the south-east of England, it will be 

 seen that we refer their excavation chiefly to the ocean. We 

 are aware that we cannot generalize these views and apply 

 them to the valleys of all parts of the world, In Central 

 France, for example, rivers and land-floods, co-operating with 

 earthquakes, have deeply intersected the lacustrine and volcanic 

 deposits, and have hollowed out valleys as deep, perhaps, as 

 any in our Weald district. In what manner these effects may 

 be brought about in the course of time, by the action of run- 

 ning water, even without the intervention of the sea, may be 

 understood by what we have said of the removal of rock by 

 aqueous agency during the Calabrian earthquakes *. 



Those geologists who contend that the valleys in England 

 are not due to what they term ( modern causes,' are in the 

 habit of appealing to the fact, that the rivers in the interior of 

 England are working no sensible alterations, and could never, 

 in their present state, not even in millions of years, excavate 

 the valleys through which they now flow. We suspect that a 

 false theory is involved even in the term ' modern causes,' as 

 * Vol, i, chap. xxiv. 



