54 THE LAPSE OP TIME. [Chap. X. 



origin in chief part to the rocks of which they are com- 

 posed having resisted subaerial denudation better than 

 the surrounding surface; this surface consequently has 

 been gradually lowered, with the lines of harder rock 

 left projecting. Nothing impresses the mind with the 

 vast duration of time, according to our ideas of time, 

 more forcibly than the conviction thus gained that sub- 

 aerial agencies which apparently have so little power, 

 and which seem to work so slowly, have produced great 

 results. 



When thus impressed with the slow rate at which 

 the land is worn away through subaerial and littoral 

 action, it is good, in order to appreciate the past dura- 

 tion of time, to consider, on the one hand, the masses 

 of rock which have been removed over many extensive 

 areas, and on the other hand the thickness of our sedi- 

 mentary formations. I remember having been much 

 struck when viewing volcanic islands, which have been 

 worn by the waves and pared all round into perpen- 

 dicular 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 up- 

 heaved 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 slow and effected by many starts, the sur- 

 face 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 



