Cfl. XIX.] DENUDATION OF THE WEALD. 375 



tidal action. As to the power of mere atmospheric causes, we have 

 only to endow them with a small portion of the force ascribed to them 

 by the geologists in question, and we can have no difficulty in explain- 

 ing how all traces of the sea in the shape of littoral shells or beach 

 deposits should have disappeared. Shells, once strewed over ancient 

 shores, may have decomposed so as to make it impossible for us to 

 assign an exact palseontological date to the period of emergence ; but 

 the leading inequalities of hill and dale, the long lines of escarpment, 

 the longitudinal and transverse valleys, may still be mainly due to the 

 power of the waves and currents of the sea. 



In despair of solving the problem of the present geographical con- 

 figuration and geological structure of the Weald by an appeal to 

 ordinary causation, some geologists have been fain to invoke the aid 

 of imaginary " rushes of salt water " over the land during the sudden 

 upthrow of the bed of the sea, when the anticlinal axis of the Weald 

 was formed. Others refer to vast bodies of fresh water breaking 

 forth from subterranean reservoirs, when the rocks were riven by 

 earthquake shocks of intense violence. The singleness of the cause 

 and the unity of the result are emphatically insisted upon : the catas- 

 trophe was abrupt, tumultuous, transient, and paroxysmal ; fragments 

 of stone were swept along to great distances without time being- 

 allowed for attrition ; alluvium was thrown down unstratified, and 

 often in strange situations, on the flanks or on the summits of hills, 

 while the lowest, levels were left bare. The convulsion was felt simul- 

 taneously over so wide an area, that all the individuals of certain spe- 

 cies of quadrupeds were at once annihilated ; yet the event was com- 

 paratively modern, for the species of testacea now living were already 

 in existence. 



This hypothesis is untenable and unnecessary. In the present 

 chapter I have endeavored to show how numerous have been the 

 periods of geographical change, and how vast their duration. Evi- 

 dence to this effect is afforded by the relative position of the chalk 

 and overlying tertiary deposits ; by the nature, character, and posi- 

 tion of the tertiary strata ; and by the overlying alluvia of the Weald 

 and adjacent countries. As to the superficial detritus, its insignifi- 

 cance in volume, when compared to the missing rocks, should never 

 be lost sight of. A mountain-mass of solid matter, hundreds of 

 square miles in extent, and hundreds of yards in thickness, has been 

 carried away bodily. To what distance it has been transported we 

 know not, but certainly beyond the limits of the Weald. For achiev- 

 ing such a task, if we are to judge by analogy, all transient and sud- 

 den agency is hopelessly inadequate. There is one power alone which 

 is competent to the task, namely, the mechanical force of water in 

 motion, operating gradually and for ages. We have seen in the sixth 

 chapter that every stratified portion of the earth's crust is a monu- 

 ment of denudation on a grand scale, always effected slowly ; for each 

 superimposed stratum, however thin, has been successively and sepa- 



