Ch. VI.] 



INTENSITY OF AQUEOUS CAUSES. 



107 







iafln 







n: 





:: 



1 » 





i* 



us* 8 



•f ' 



. 





1 





to 



etable 



number 



months, or years for the attainment of maturity, and the per- 

 petuation of its species by generation; and thus the first 

 approach was made to the conception of a common standard 

 of time, without which there are no means whatever of 



measuring the com 



events has taken place at two distinct periods. This 

 standard consisted of the average duration of the lives of 



individuals of the same genera or families in the animal and 

 vegetable kingdoms ; and the multitude of fossils dispersed 

 through successive strata implied the continuance of the 

 same species for many generations. At length the idea that 

 species themselves had had a limited duration, arose out of 

 the observed fact that sets of strata of different ages con- 

 tained fossils of distinct species. Finally, the opinion became 

 general, that in the course of ages, one assemblage of animals 

 and plants had disappeared after another again and again, 



Denudation. 



them. 

 )d from 



remains, the forms of stratification led also, on a fuller in- 

 vestigation, to the belief that sedimentary rocks had been 

 slowly deposited ; but it was still supposed that denudation, 

 or the power of running water, and the waves and currents 

 of the ocean, to strip off superior strata, and lay bare the 



formerly 



energy wholly 



unequalled in our times. These opinions were both illogical 

 and inconsistent, because deposition and denudation are 

 processes inseparably connected, and what is true of the rate 



must 



matter 



particular region can only keep pace with its removal from 

 another, so that the aggregate of sedimentary strata in the 

 earth's crust can never exceed in volume the amount of 

 solid matter which has been ground down and washed away 

 by rivers, waves, and currents. How vast then must be the 

 spaces which this abstraction of matter has left vacant ! how 

 far exceeding in dimensions all the valleys, however nume- 

 rous, and the hollows, however vast, which we can prove to 

 have been cleared out by aqueous erosion ! the evidences of 



