THE INSULATION OF ST. MICHAEL'S MOUNT. 5 
Turning next to the hypothesis of insulation through sub- 
sidence—the only alternative consistent with the assumptions 
made at the beginning—I proceeded to show that there had been 
a general eal movement of the land in geologically very. 
recent times, and, as evidence of it, described the submerged 
forests so prevalent on both the north and south coasts of Devon 
and Cornwall, especially noting the fine and well-known descrip- 
tion which, in 1822, Dr. Boase gave of the example in the Mount’s 
Bay.* I dwelt at some eae lh on the fact that, whilst mere 
encroachment necessarily destroys and removes the land it wastes, 
subsidence may leave intact the soil it overwhelms; and, con- 
versely, that when an old vegetable soil is found undisturbed 
beneath the sea, when the stumps of trees are found projecting 
vertically through and perpendicular to it, when roots and 
rootlets ramify from the trunks horizontally through the soil, 
when the plants are all of kinds still indigenous to the districts, 
and when such phenomena are met with in numerous localities 
throughout a wide area, there can be no doubt that there has been 
a general, tranquil, and in a geological sense, a very recent subsi- 
dence of the land. 
Next, I pomted out that whilst, on the one hand, this change 
of level could not have taken place within the last 1,900 years, 
since, about 9 B.C., the Mount was described by Diodorus Siculus 
in terms which apply admirably to it at present; on the other 
hand, the vegetable and animal remains in the forests showed that 
it was what a geologist would call a very recent event. In short, 
the evidence then before us, was such as to compel the belief that 
the insulation of the Mount had taken place before the Christian 
era, but such also as to permit the belief that the event might 
have occurred not very long before that time. 
The paper concluded thus :—‘“ A careful consideration of all 
the facts of the case, as well as of the related phenomena, points 
decidedly to the conclusion that, since Cornwall was inhabited by 
a race speaking the British language, St. Michael’s Mount was a 
‘hoar rock in a wood,’ and that its insulation resulted from a 
general subsidence of the country.” 
*“ Observations on the Submersion of part of the Mount’s Bay; and 
on the Inundation of Marine Sand on the north coast of Cornwall.” By 
‘ Henry Boase, Esq., Trans. Roy. Geol. Soe. of Cornwall, vol. ii, p. 129, et. seq. 
