496 
SILURIA. 
[Chap. XX. 
graphy " *. He alludes to " regions of convulsion, in which (in historic 
times) rocks have been rent asunder, the surface has been forced up into 
ridges, chasms have been opened out, or the ground throughout large spaces 
has been permanently lifted up above or let down beneath its former 
level.' ' If such small results have been shown to man, why not admit 
that in former times the causation may have been more intense ? 
Further on, in the same instructive volume, we find that, in estimating 
the aggregate result of diurnal operations multiplied by time, he justly 
repudiates the idea of violent catastrophes and revolutions which affected 
the " whole earth and its inhabitants." 
Not being one of those who ever held such an opinion, I have but to 
express my agreement with Sir Charles's present view, " that the more 
impressive efforts of subterranean power, such as the upheaval of moun- 
tain-chains, may have been due to multiplied convulsions of moderate 
intensity, rather than to a few paroxysmal explosions "f. I only beg 
to reassert the belief I have long entertained from evidences before me, 
that those ' convulsions ' were infinitely more powerful than any one of 
which history records an example. I infer, indeed, that each of those 
upheavals or depressions which gave rise to terraces of marine shells at 
separate heights upon our lands or to submerged lines of coast must have 
displaced large volumes of water possessing great denuding power. On the 
contrary, if the bottoms of seas had always been gradually raised, or 
the lands equably and slowly depressed (as is said to be now the case in 
Scandinavia), the currents of the ocean at such times could never have 
acted with force sufficient to denude the adjacent lands; for it is well 
known, I repeat, that deep seas never sweep away broken materials, and 
only accumulate fine silt or minute organic bodies. 
Before I quit this branch of the general subject of geology, which treats 
of the physical agencies which have brought the earth's crust into its 
present outline, I must further be permitted to express my dissent from 
those who would account for the production of all valleys and gorges by 
the action of the water that has flowed in them. I fully admit that, in 
mountainous regions, rivers, whether flowing or in the form of glaciers, 
have abraded and deepened their channels. I further admit that in vol- 
canic regions rivers descending from considerable heights into plains have 
* See 4 Principles of Geology,' edit. 1866, vol. i. formity of causation as respects the enormously 
pp. 120, 310, 318. long and undisturbed periods required to account 
t In a sketch of the life and writings of my for the accumulation of the thick sedimentary de- 
lamented friend the late Dr. Whewell, Master of posits. On the other hand, unbiased Uniformi- 
Trinity College, Cambridge, I used these words: — tarians now admit of occasional catastrophic 
" In speaking of Uniformitarians, as Whewell action ; and, as the question is thus reduced to be 
denned those geologists to be whose leader is my one of degree only — that degree to be fairly 
eminent friend Lyell, the worthy inheritor of the gauged by measuring the relations and extent of 
mantle of Hutton and Playfair, let it not be sup- the ruptures of the crust of the earth — I feel con- 
posed that any reasonable geologist, certainly not fident that out of fair discussion the exact truth 
myself, who may dwell upon the great and sudden will ultimately be obtained." — Address at the An- 
dislocations which he believes the crust of the niversary Meeting of the Eoyal Geographical So- 
earth underwent from time to time in far bygone ciety, May 1366. Trans. Roy. Geograph. Soc vol. 
periods, is not also a strenuous advocate of an uni- xxxvi. p. cxxiv. 
