President of the Geological Society for 1850. 27 



selves into smaller spaces than those which they previously 

 occupied. If this be true, the contortions and foldings of 

 pliant beds, and the fracture and dislocation of the more un- 

 yielding rocks, have frequently been due to movements as 

 gradual as those of various ages to which I have been 

 alluding. 



The imagination may well recoil from the vain effort of 

 conceiving a succession of years sufficiently vast to allow of 

 the accomplishment of contortions and inversions of stratified 

 masses like those of the higher Alps ; but its powers are 

 equally incapable of comprehending the time required for 

 grinding down the pebbles of a conglomerate 8000 feet in 

 thickness. In this case, however, there is no mode of evad- 

 ing the obvious conclusion, since every pebble tells its own 

 tale. Stupendous as is the aggregate result, there is no 

 escape from the necessity of assuming a lapse of time suffi- 

 ciently enormous to allow of so tedious an operation. No 

 intervention of a cataclysm or series of paroxysmal waves 

 can avail us ; and if the geologist could abridge the period, 

 he would find that far from being a gainer, he had deprived 

 himself of the only means ever yet suggested of explaining 

 another set of geological monuments, relating to what we 

 term denudation. It is not simply by fixed and permanent 

 inequalities of level, in the land and sea, or by the alterna- 

 tion of dry and rainy seasons, or of summer heat and winter's 

 frost, that the aqueous action of torrents, rivers, breakers, 

 tides, and currents acquires a sustained energy, capable of 

 denuding wide areas, but by the gradual elevation or subsid- 

 ence of continents and islands, occasionally accompanied by 

 many minor oscillations of level. It is by reiterated slight 

 variations in the position of a coast line, by the continual 

 shifting of the points of attack, that every portion of the sur- 

 face of the land is exposed by turns to denudation, and is 

 prevented from ever settling into a state of equilibrium and 

 cessation from waste. If earthquakes agitate the country 

 from time to time, while it is rising or sinking, so as to 

 block up valleys and cause temporary lakes and fissures, or 

 the fall of river-cliffs and sea-cliffs, the power of aqueous 

 destruction will be still further augmented. 



