270 '^^iE LAPSE OF TIME. CiiAr. IX. 



and those ranging across England, which formerly were looked 

 at by every one Jis ancient sea-coasts, cannot have been thus 

 formed, for each line is composed of one and the s;une forma- 

 tion, while our j^resent sea-clifls are eveiywhere formed by the 

 intersection of various formations. This being tlic case, we 

 are compcllcil to admit that the escaq^ments owe their origin 

 in chief part to the rocks of Avhich they are composed having 

 resisted subacrial denudation better than the surrounding sur- 

 face ; this surface consequently has l^een gradually lowered, 

 with the lines of harder rock left projecting. Nothing im- 

 presses the mind with the vast duration of time, according to 

 our ideas of time, more forcibly tlian the conviction thus gained 

 that subaiirial agencies, which apparently have so little power, 

 and which seem to work so slowly, have produced such great 

 results. 



When thus impressed with the slow rate at Vv'liich tlie land 

 is worn away through subaerial and littoral action, it is good, 

 in order to appreciate the past duration of time, to consider, on 

 the one hand, the mass of rock which has been removed over 

 many extensive areas, and on the other hand the tliickness of 

 our sedimentary formations. I remember haAnng been much 

 struck M'hen viewing volcanic islands, which have been worn 

 by the waves and pared all around into perpendicular cliffs of 

 one or two thousand feet in height ; for the gentle slope of 

 the lava-streams, due to their formerly liquid state, showed at 

 a glance how far the hard, rocky beds had once extended into 

 the open ocean. The same story is told still more plainly by 

 faults — those great cracks along which the strata have been 

 upheaved on one side, or thrown down on the other, to the 

 height or depth of thousands of feet ; for since the crust cracked, 

 and it makes no great difference whether the upheaval was 

 sudden, or, as most geologists now believe, was very slow and 

 eflected by many starts, the surface of the land has been so 

 completely planed down that no trace of these vast dislocations 

 is externally visible. The Craven fault, for instance, extends 

 for upward of thirty miles, and along this line the vertical dis- 

 placement of tlie strata varies from 600 to 3,000 feet. Prof, 

 liamsay has published an account of a downtlirow in Anglesea 

 of 2,300 feet; and lie informs me tliat he fully believes that 

 tliere is one in ]M(>rionethshire of 12,000 feet; yet in these 

 cas(>s there is nothing on the sm-face of the land to show such 

 prodigious movements ; tlie jiile of rocks on cither side of the 

 crack having been smoothly SAvej)t away. 



