164 ARE SOILS EXRICHED, IMPOVERISHED, pt. m. 



disappear most quickly, possibly from a freer access 

 and action of rain water in disintegration, and possi- 

 bly also from roots inserting themselves in crevices, 

 and, by turgescence, detaching blocks bodily. Besides 

 this, roots in decay generate carbonic acid, which is a 

 great disintegrator. Independently of porousness^ vol- 

 canic cones are milikely to have ravines or gullies, 

 since their shape tends to diffuse, instead of to concen- 

 trate, any run of water. In fact, the tendency of dis- 

 integration and the wash of rain would be to form 

 cones out of single hills, and ridges out of chains of 

 hills, with projecting spurs, each spur being itself a 

 ridge, ending in a half-cone : and even these ridges 

 are so studded with cones as to have a serrated or 

 saw-hke outline, and to have earned the modern 

 Spanish, Portuguese, and Italian name of sierra, or 

 serra, and to have originated the Latin expression of 

 21 er jug a montium ; the very name of hills being taken 

 from the yohe-YikQ appearance of contiguous cones. 



For this reason, though, as Sir Humphry Davy . 

 finely remarks, no work of mortal can be immortal, 

 those works of man which approach nearest to immor- 

 tality are cones,- — the pyramid, the tumulus, and the 

 cairn. Why do the imher edax and the fuga temporum 

 pass with so hght a touch over these ? Because they 

 begin with a form which others end in,— a form which 

 is not deformed even by disintegration and the wash 

 of rain. 



Iq comparison to the broad waste from the wash of 



