i PROLEGOMENA. 3 



but a fleeting phase of her infinite variety; merely 

 the last of the series of changes which the earth's 

 surface has undergone in the course of the mil- 

 lions of years of its existence. Turn back a square 

 foot of the thin turf, and the solid foundation of 

 the land, exposed in cliffs of chalk five hundred 

 feet high on the adjacent shore, yields full assur- 

 ance of a time when the sea covered the site of the^ 

 " everlasting hills "; and when the vegetation of 

 what land lay nearest, was as different from the 

 present Flora of the Sussex downs, as that of Cen- 

 tral Africa now is.* No less certain is it that, be- 

 tween the time during which the chalk was formed 

 and that at which the original turf came into exist- 

 ence, thousands of centuries elapsed, in the course 

 of which, the state of nature of the ages during 

 which the chalk was deposited, passed into that 

 which now is, by changes so slow that, in the com- l 

 ing and going of the generations of men, had 

 such witnessed them, the contemporary conditions 

 \\ould have seemed to be unchanging and un- 

 changeable. 



But it is also certain that, before the deposition 

 of the chalk, a vastly longer period had elapsed, 

 throughout which it is easy to follow the traces 

 of the same process of ceaseless modification and 

 of the internecine struggle for existence of living 

 things; and that even when we can get no further 



* See " On a piece of Chalk " in the preceding volume 

 of these Essays (vol. viii. p. 1). 



