254 ON THE ORIGIN OF SPECIES 



few miles any line of rocky cliff, which is undergoing 

 degradation, we find that it is only here and there, along 

 a short length or round a promontory, that the cliffs 

 are at the present time suffering. The appearance of 

 the surface and the vegetation show that elsewhere 

 years have elapsed since the waters washed their base. 

 He who most closely studies the action of the sea on 

 our shores, will, I believe, be most deeply impressed 

 with the slowness with which rocky coasts are worn 

 away. The observations on this head by Hugh Miller, 

 and by that excellent observer Mr. Smith of Jordan 

 Hill, are most impressive. With the mind thus im- 

 pressed, let any one examine beds of conglomerate 

 many thousand feet in thickness, which, though prob- 

 ably formed at a quicker rate than many other 

 deposits, yet, from being formed of worn and rounded 

 pebbles, each of which bears the stamp of time, are 

 good to show how slowly the mass has been accumu- 

 lated. In the Cordillera I estimated one pile of con- 

 glomerate at ten thousand feet in thickness. Let the 

 observer remember Lyell's profound remark that the 

 thickness and extent of sedimentary formations are the 

 result and measure of the degradation which the earth's 

 crust has elsewhere suffered. And what an amount 

 of degradation is implied by the sedimentary deposits 

 of many countries ! Professor Ramsay has given me 

 the maximum thickness, in most cases from actual 

 measurement, in a few cases from estimate, of each 

 formation in different parts of Great Britain ; and this 

 is the result : — 



Feet. 



Palaeozoic 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 forma- 

 tion, we have, in the opinion of most geologists, 



