16 THE INSULATION OF ST. MICHAEL’S MOUNT. 
forest, was a mere local slip, in which neither the Mount. nor its 
isthmus participated. To this aspect we will now give atten- 
tion. We know that a forest of the kind extends continuously 
from about midway between the Mount and Penzance to Newlyn, 
and probably sea-ward at least to the well-known roadstead 
known as Gwavas Lake; that there are indications of another— 
if, indeed, it is another—as far west as Lamorna Cove; and that 
a third occurs at Porthleven, seven miles E.S.E. from the Mount ;* 
hence, were there no further evidence of this kind, it seems 
impossible to conclude that the subsidence was so local as not to 
include the Mount. The evidence, however, is far from being so 
limited, for similar forests are known to exist on all the shores of 
all the British seas and channels. In 1829, Mr. Colenso, when | 
describing in considerable detail the Stream-works at Pentuan in 
Mevagissey Bay, stated that at the top of the “tin ground,” nearly 
fifty feet below spring-tide high water, stumps of trees, including 
oaks, were found having their roots in their natural position, and 
traceable to their smallest fibres even so deep as two feet ;T and 
in the same year Mr. Henwood described the Carnon section on 
a branch of the Fal, and mentioned a vegetable bed containing 
moss, leaves, nuts, and remains of mammals, at a depth of nearly 
seventy feet below the high-water level.t It is well known that 
such forests present themselves at Millendreth, near Looe, in Kast 
Cornwall; and in the Lower St. Columb valley,§ as well as in 
Padstow harbour, in the north of the county. In Devonshire, 
too, they are equally well known, as they occur at Bovisand in 
Plymouth Sound, at Thurlestone Sands in Bigbury Bay, in Salcombe 
Harbour, at Blackpool near Dartmouth, in Torbay, and in Bideford 
Bay. They are met with also near Bridgewater and Porlock in 
Somersetshire, on several parts of the coast of Wales, on the 
coast of Cheshire, and near Hull. In short, it is difficult to say 
where they have not been seen. 
Some of them are but rarely exposed to view. Thus, the 
Thurlestone example was seen and described in the spring of 1866, 
by the Rev. P. A. Ilbert, rector of the parish, who, though he had 
* Trans. Roy. Geol. Soc. of Cornwall, vol. i, p. 236. 
+ Ibid, vol. iv, p. 29, &e. 
+ Ibid, p. 57, &e. 
§ See De la Beche’s Report on Cornwall, &c., p. 405, 1839. 
