24 THE INSULATION OF ST. MICHAEL'S MOUNT. 
III. We have seen that the entire country, prior to the sub- 
sidence, stood at least 70 feet higher than at present ; consequently 
the cliffs now assailed by the waves during storms at spring-tide 
high-water, were then at some distance beyond their reach, or, 
more correctly, they have been formed by wave action on sites to 
which the breakers then had no access; whilst the rocks and 
shoals on which the waves then broke at spring-tide low-water, are 
now in the quiet depths of the sea. Hence the breadth of the 
existing foreshore—that is, the entire distance between the line of 
breakers in the most tempestuous weather at the lowest retreat of 
the tide, and the cliffs which the waves attack in similar weather 
at the high water of spring tides—may be taken as the space over 
which the cliffs have slowly retreated, inch by inch, since the last 
adjustment of the relative level of sea and land. 
It cannot be necessary to remark that this amplitude of the 
existing foreshore differs much in different districts, for it depends 
on the materials of which the rocks consist, their structure, the 
aspect of their exposure, and the prevalent winds. Though the 
coast from the Prawle to the Start in South Devon is undoubtedly 
exposed to the almost unchecked fury of the waves sent up channel 
from the Atlantic, yet, when it is remembered that the rocks of 
that district are crystalline schists, than which none probably are 
more capable of resistance, it will be seen that the fact that even 
they have so far retreated since the submergence of the forests as 
to form a foreshore fully a quarter of a mile in breath, is one 
which, to the man of science, betokens that the era of the subsi- 
dence must have been in remote pre-Christian times. 
Remote, however, as was this era when measured by the units 
employed in human history, it must have been very modern as a 
geological event, for, as we have already seen, the plants of which 
the forests consist are, not only recent species, but such as are still 
indigenous in the several localities; hence the period of their 
growth—a period necessarily more ancient than that of their 
submergence—fails to take us back to the times of extinct vegeta- 
tion, or to a climate differing much, if at all, from that which at 
present obtains. 
It must be borne in mind, however, that this by no means 
proves that the animals of the period and districts have undergone 
no change, for, to say nothing of the influence of man in the 
