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. xxiy. 
