Chap. XX.] 
INTENSITY OF FORMER CAUSES. 
491 
called Quaternary or Post-pliocene, the former sea-beaches or marine shelly 
deposits of those days usually lie either in separate terraces or in patches 
at distinct and different altitudes, varying from a few feet above the sea- 
line to great altitudes, as at Moel Tryfane in North Wales, where existing 
Arctic shells lie at upwards of 1300 feet above the sea. These evidences 
demonstrate that such oscillations were not caused by a continuous and 
equable expansion or contraction of the crust, but by intermittent agen- 
cies of sudden activity following long periods of repose. They are, in 
short, proofs of a former intensity of causation, as contrasted with the 
uncertain signs of gradual elevation or depression that are appealed to 
as having occurred within the historic era. The case therefore stands 
thus. The shelly and pebbly terraces which exist are signs of sudden ele- 
vations at different periods ; whilst the theory of modern gradual elevation 
and depression is still wanting in any valid proof that such operations 
have taken place except within very limited areas. Much longer and more 
persistent observations must indeed be made before any definite conclusion 
can be reached respecting the rate of gradual elevation or depression which 
has been going on in the last thousand years, though we may confidently 
assert that such changes in the relations of land to water in the historical 
period have been infinitesimally small when compared with the many ante- 
cedent geological operations. 
One of the reasons which has been adduced in favour of long and gra- 
dual changes is that on the coast of Norfolk there exists a submarine pre- 
glacial forest, where the stems of the trees are still standing erect, with 
their roots in the ancient soil in which they grew. That ancient soil is 
covered by other younger deposits, including the Drift, and in it are found 
bones of Elephants, Hippopotami, and other animals, and of other extinct 
and living Mammalia*. Now, so far from seeing in this commixture, and 
in the vertical stumps of trees, the indications of long and slow action, I 
view them as evidences of a sudden movement. 
When examining a similar submarine forest, with the trunks of the trees 
still erect, the late eminent Dr. Forchhammer, of Copenhagen, came to the 
conclusion, as he informed me, that the movement by which they were 
submerged must have been sudden. He argued that the rapid immersion 
of the trunks, and their having been quickly surrounded by marine mud, 
could alone have preserved them ; for if the trees had been gradually sink- 
ing at the rate of an inch or two in a year, they would have been entirely 
decomposed under the atmosphere long before their submergence, and thus 
no trace of their trunks would have remained. 
Wherever we see an enormous quantity of the fractured bones of com- 
mon land animals huddled together, as in many cases, with those of huge 
Hippopotami, I naturally infer that we have in this admixture good proofs 
of a catastrophic destruction of such animals. As one example of thisphe- 
* Lyell, Elements of Geology, 6th edit. p. 160. 
