290 CONCLUSION. [Ch. XIX 



distances without time being allowed for attrition ; alluvium was thrown 

 down imstratified, and often in strange situations, on the flanks or on the 

 summits of hills, while the lowest levels were left bare. The comnilsion 

 was felt simultaneously over so wide an area that all the individuals of 

 certain species of quadrupeds were at once annihilated ; yet the event was 

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

 in existence. 



This hypothesis is surely 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. Evidence to this 

 effect is afforded by the relative position of the chalk and overlying ter- 

 tiary deposits ; by the nature, character, and position of the tertiary 

 strata ; and by the overlying alluvia of the Weald and adjacent countries. 

 As to the superficial detritus, its insignificance 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 w^hat distance it has been 

 transported we know not, but certainly beyond the limits of the Weald. 

 For achieving such a task, if we are to judge by analogy, all transient and 

 sudden 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 6 th chapter 

 that every stratified portion of the earth's crust is a monument of denuda- 

 tion on a grand scale, always eftected slowly ; for each superimposed 

 stratum, however thin, has been successively and separately elaborated. 

 Every attempt, therefore, to circumscribe the time in which any great 

 amount of denudation, ancient or modern, has been accomplished, draws 

 with it the gratuitous rejection of the only kind of machinery known to 

 us which possesses the adequate power. 



If, then, at every epoch, from the Cambrian to the Pliocene inclusive, 

 voluminous masses of matter, such as are missing in the Weald, have 

 been transferred from place to place, and always removed gradually, it 

 seems extravagant to imagine an exception in the very region where we 

 can prove the first and last acts of denudation to have been separated by 

 so vast an interval of time. Here, might we say, if anywhere within the 

 range of geological inquiry, we have time enough and without stint at 

 our command. 



