490 
SILUEIA. 
[Chap. XX. 
one side, showing abrupt, clean, vertical abscission from those of the other. 
Then follow up, on each opposite cliff, the twisted and often inverted lines 
of torsion by which the Tertiary strata are crumpled up with the Secondary 
rocks, particularly on the east side of that great hollow, even to the sum- 
mit of the mountain. 
Let the traveller proceed to the other parts of this convoluted and broken 
chain, and gaze on the grandeur of the metamorphic action by which bands 
of fossiliferous limestone have been transmuted suddenly in their horizontal 
range into crystalline gypsum ; and then let him ask himself if he believes 
that the agency which produced such enormous and abrupt changes was of 
no greater intensity than that which prevails in our times. Undoubtedly 
the vera causa of metamorphism is still present, since we see that, at the 
Baths of Aix in Savoy, in the western Alps, and at other places, the sul- 
phuric acid, when liberated from the mineral water, does produce a film of 
gypsum on the surface of the limestone walls ; but how believe that the 
agent which in our day works on a scale of inches in many years, is of the 
same intensity as that which operated throughout a whole range of lofty 
mountains ? how are we to explain that, by gradual operations, the strata 
composed of carbonate of lime through a thickness of thousands of feet 
are all at once, and on the same horizon, changed from bottom to top into 
sulphate of lime ? 
Let it not be supposed that we, who hold to the proofs of more powerful 
causation in ancient periods, do not fully admit that the former physical 
agencies were of the same nature as those which now prevail. We simply 
assert, on the countless evidences of fracture, dislocation, metamorphism, 
and inversion of the strata, and also on that of vast and clean- swept de- 
nudations, that these agencies were from time to time infinitely more ener- 
getic than in existing nature, — in other words, that the metamorphisms and 
oscillations of the terrestrial crust, including the uprise of sea-bottoms, and 
the sweeping out of debris, were paroxysmal in comparison with the move- 
ments of our own era. We further maintain that no amount of time (of 
which no true geologist was ever parsimonious when recording the history 
of bygone accumulations of sediment, or of the different races of animals 
they contain) will enable us to account for the signs of many great breaks 
and convulsions which are visible in every mountain-chain, and which the 
miner encounters in all underground workings. 
If slow and uninterruptedly gradual risings of land from beneath the sea, 
or depressions beneath it, had taken place during any one even of the recent 
geological periods during which the earth has undergone many changes, 
ought we not to see repeated evidences of such former out-swellings in 
the presence of sea-shells and pebbles and marine debris extending in slopes 
on many sides of continents and islands, from the sea upwards to consider- 
able heights ? Instead of such signs, of which no example has been indi- 
cated, we constantly find that even in the latest geological times, whether 
