492 
SILUEIA. 
[Chap. XX. 
nomenon, I have cited the mixed and angular flint- and bone-drift with 
remains of Stags, Mammoths, and Hippopotami on the flanks of the chalk 
cliffs of Brighton *. 
Then, if we pass from the subject of elevation or depression of lands 
to that of their denudation, how can the believers in the power of the 
gradual action of the sea explain the wonderful results of erosion which 
present themselves on the surface of rocks of all ages ? For if we look 
to the agency of present seas, we know that the deep ocean never erodes, 
and that, on the contrary, perfect tranquillity reigns at its base. If, then, 
denudation in our time is produced only by breakers or by waves acting on 
coast-lines, which have, we know, a wasting and denuding power over 
limited regions, how account for the perfectly clean sweep which has been 
made of wide tracts ? With the exception of ordinary submarine currents, 
to which many continents must have been subjected, what more natural 
method of explaining these facts than by referring them to the translation 
by vast bodies of water suddenly put into action by those upheavals of 
parts of the earth of which we have clear evidence ? Judging from the 
fact that marine gravel and shells do often lie in terraces, at different alti- 
tudes on the sides of our mountains, must it not in fairness be admitted that 
each of the upward sudden movements leaving such a terrace must have 
given rise to waves of such magnitude and force as would sweep over and 
scour the low tracts, destroying land animals in their course, and mixing 
them up with those of aquatic habits? How explain the mixture of bones 
of all sorts of animals except by some such catastrophes ? I do not here 
invoke any violation of the laws of nature. I only ask practical geologists 
to look at the proofs we possess of sudden dislocations and upheavals of the 
land, and then reflect upon what must have been the corresponding effects of 
the water displaced. How account for the tons of fractured bones of Hippo- 
potami, huddled together, as we know, in crevices and caverns of the rocks 
of Sicily, except by some such violent action ? Let not beginners in geology 
be led away by those who, deriding 1 convulsionists ' and ' catastrophists,' 
repudiate data which many men who have passed their lives in the study 
of the dismemberments of the rocks think are inexplicable without ap- 
pealing to much more powerful causes than any of which history records 
an example. 
Has the advocate who would account for all such dismemberments 
by long continuance only of existing causes, whether by the active ero- 
sion of breakers on a shore or by atmospheric action, ever satisfactorily 
accounted for the complete and entire denudation of our clean-swept 
1 valleys of elevation ' ? Let him inspect that British model of such phe- 
nomena, the Silurian valley of elevation at Woolhopc, first described by 
myself f. What agency, I ask, except that of very powerful currents of 
* Sec my Memoir thereon, Quart. Journ. Geol. to the removal of the enormous masses of Old 
Soc. vol. vii. pp. 349 &c. Red Sandstone which must formerly have covered 
t See ' Silurian System,' p. 427. After alluding this insulated valley, and to the clean sweep of all 
