IMPERFECTION OF GEOLOGICAL RECORD 61 



account of a downthrow in Anglesea of 2,300 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 sedimentary 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 Eamsay has given me the maximum 

 thickness, from actual measurement in most cases, of the 

 successive formations in different parts of Great Britain; 

 and this is the result: 



Feet 



Paleozoic 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 Conti- 

 nent. Moreover, between each successive formation we 

 have, in the opinion of most geologists, blank periods of 

 enormous length. So that the lofty pile of sedimentary 

 rocks in Britain gives but an inadequate idea of the time 

 which has elapsed during their accumulation. The con- 

 sideration of these various facts impresses the mind al- 



