320 EOCENE PERIOD. [Ch. XXII. 



if it could be assumed that there were ancient causes differing 



o 



from those which are now in operation. But if we substitute 

 the phrase, existing causes, we shall find that the argument 

 now controverted amounts to little more than this, ' that in a 

 country free from subterranean movements, the action of run- 

 ning water is so trifling that it could never hollow out, in any 

 lapse of ages, a deep system of valleys, and, therefore, no known 

 combination of existing causes could ever have given rise to 

 our present valleys ! ' 



The advocates of these doctrines, in their anxiety to point 

 out the supposed absurdity of attributing to ordinary causes 

 those inequalities of hill and dale, which now diversify the 

 earth's surface, have too often kept entirely out of view the 

 many recorded examples of elevations and subsidences of land 

 during earthquakes, the frequent fissuring of mountains, and 

 opening of chasms,, the damming up of rivers by landslips, 

 the deflection of streams from their original courses, and more 

 important, perhaps, than all these, the denuding power of the 

 ocean, during the rise of our continents from the deep. Few 

 of the ordinary causes of change, whether igneous or aqueous, 

 can be observed to act with their full intensity in any one place 

 at the same time ; hence it is easy to persuade those who 

 have not reflected long and profoundly on the working of 

 the numerous igneous and aqueous agents, that they are en- 

 tirely inadequate to bring about any important fluctuations in 

 the configuration of the earth's surface. 



Recapitulation. We shall now briefly recapitulate the con- 

 clusions to which we have arrived respecting the geology of 

 the south-east of England, in reference to the nature and origin 

 of the Eocene formations considered in this and the two pre- 

 ceding chapters. 



1. In the first place, it appears that the tertiary strata rest 

 exclusively upon the chalk, and consist, with some trifling ex- 

 ceptions, of alternations of clay and sand. 



2. The organic remains agree with those of the Paris basin, 

 but the mineral character of the deposit is extremely different, 



