THE INSULATION OF ST. MICHAEL'S MOUNT. 17 
resided there 25 years, and had interested himself in the local 
geology, had never previously seen or heard of it, though he had 
frequently noticed that lumps of what proved to be the forest clay 
were cast up by the waves, and had been much puzzled to account 
for them. There isa local tradition, however, that an old wood 
once stood on Thurlestone Sands; and this, in all probability, rests 
on no other foundation than the submerged forest thus very rarely 
exposed.* 
Again, the splendid instance at Blackpool was seen in 1802 
and in 1865, by persons who described it to me; but there is 
reason to believe that it remained completely buried beneath the 
sand during the entire interval. It was exposed again in Feb- 
ruary 1869. 
These forests have been described by so many observers that 
their literature is quite voluminous. Having devoted a large 
amount of attention to these descriptions, and having had opportu- 
nities of carefully studying the examples at Millendreth, Blackpool, 
Torbay, Bideford Bay, and the really magnificent one between the 
Mersey and the Dee, I am prepared to state that they uniformly 
present the same phenomena. They are everywhere composed 
exclusively of plants still indigenous to the several localities ; the 
stumps of the trees rise vertically through, and at right angles 
to, the soil, in which the roots and rootlets ramify horizontally ; 
and there is an entire absence of any indications of local slips. 
With such a body of fact before us it may be safely concluded 
that they are the remains of forests in situ ; that they were carried 
to their present level by a general, uniform, and tranquil subsi- 
dence of, at least, Western Europe, including the British archi- 
pelago—a subsidence, in fact, similar to that at present in pro- 
gress in West Greenland,—in which we may feel confident St. 
Michael’s Mount and its isthmus participated, the former being 
thereby converted into the half-island we now see it. 
Ill. The answer to the third question has been already and 
obviously indicated, and need not be enlarged on. There may or 
may not have been some portion of soil on the isthmus, and this 
may or may not have been occupied by trees; but this, in either 
* See Trans. Devon. Assoc., Vol. i, pt. v, pp. 77-9, 1866. 
+ Lbid, vol. iii, pp. 127-9, 1869. 
