CHAP. X.] THE LAPSE OF TIME. 251 



order to appreciate the past duration 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 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 slow 

 and effected 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 

 upwards of 30 miles, and along this line the vertical displacement 

 of the strata varies from 600 to 3000 feet. Professor Ramsay has 

 published an account of a downthrow in Anglesea of 2300 feet ; 

 and he informs me that he fully believes that there is one in. 

 Merionethshire of 12,000 feet ; yet in these cases there is nothing 

 on the surface of the land to show such prodigious movements; 

 the pile of rocks on either side of the crack having been smoothly 

 swept away. 



On the other hand, in all parts of the world the piles of sedi- 

 mentary strata are of wonderful thickness. In the Cordillera I 

 estimated one mass of conglomerate at ten thousand feet; and 

 although conglomerates have probably been accumulated at a 

 quicker rate than finer sediments, yet from being formed of worn 

 and rounded pebbles, each of which bears the stamp of time, they 

 are good to show how slowly the mass must have been heaped 

 together. Professor Ramsay has given me the maximum thick- 

 ness, from actual measurement in most cases, of the successive 

 formations in different parts of Great Britain ; and this is the 

 result : 



Feet. 



Paheozoic strata (not including igneous beds) 57,154 



Secondary strata 13,190 



Tertiary strata 2,240 



making altogether 72,584 feet ; that is, very nearly thirteen and 

 three-quarters British miles. Some of the formations, which are 

 represented in England by thin beds, are thousands of feet in 

 thickness on the Continent. Moreover, between each successive 

 formation, we have, in the opinion of most geologists, blank 

 periods of enormous length. So that the lofty pile of sedimen- 



