ANNIVERSARY ADDRESS OF THE PRESIDENT. Iv 



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 

 evading the obvious conclusion, since every pebble tells its own tale. 

 Stupendous as is the aggregate result, there is no escape from the ne- 

 cessity of assuming a lapse of time sufficiently 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 gdner, 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 alternation 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 subsidence of con- 

 tinents and islands, occasionally accompanied by many minor oscilla- 

 tions 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 surface 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. 



In the first volume of the * Memoirs of the Survey of Great Bri- 

 tain,' Professor Ramsay has shovm that the missing beds, removed 

 from the summit of the Mendips, must have been nearly a mile in 

 thickness, and he has pointed out considerable areas in South Wales 

 and some of the adjacent counties of England, where a series of pa- 

 laeozoic strata not less than 1 1,000 feet in thickness have been stripped 

 off. All these materials have of course been transported to new re- 

 gions ; and when it is shown by observations in the same * Survey ' 

 that the palaeozoic strata are from 20,000 to 30,000 feet thick, we have 

 a counterpart of older date of denuding operations on a scale of similar 



