178 
POPULAR, SCIENCE REVIEW. 
a strong barrier to the destructive force of the sea. The origin 
of this pebble ridge has not, by geologists, been determined ; 
but I think the suggestion is most correct that supposes it to 
be the result of the wash of the sea removing the beds of 
clay that overlie a layer of pebbles. This pebble bed we have, 
by excavations made in several places through the clay, been 
able 'to trace within a short distance of the pebble ridge ; 
and a recent boring, made for the purpose of obtaining water, 
has shown that, in diminished size, the pebbles exist as far up 
the sides of the shore as the stables of the Westward Ho ! Hotel. 
I think, therefore, that there can be little doubt but that the 
terrible wash of the Atlantic thins off the clay, and so exposes 
the pebble bed below to the action of the sea, which, by degrees, 
carries pebble after pebble to add to the wall that protects the 
grassy Burrows from the destructive lash of the waves. 
That the Great Pebble Eidge is moving inwards appears to be 
ascertained, but the rate of progress has not, I believe, been 
determined. But the gradual movement inwards of the Eidge, 
however fast or slow, exposes all the shore that is seaward of its 
protection to the destructive agency of the waves ; it is to this, 
and not to any variation in level of the coast line, that, I believe, 
the submergence of the forest along the shore at Northam 
Burrows is due. The beach, to a very great extent, is covered 
by sand, which, to a large degree, protects the underlying clay 
from destruction ; but that the sand is of comparatively recent 
deposition is demonstrated in the quantities of the shells of the 
Pholas dactylis that are found in the clay beneath, which must 
have lived, and burrowed their holes after the clay had been 
exposed to the action of the sea, and before the time that the 
sand was deposited on the beach ; from the presence of which 
the beach is still free for a considerable distance above low 
water mark. 
The fact, then, that the beach at the shore extremity is 
scarcely below the level of the Burrows, while the strata of 
which it is composed gradually thin out as it approximates 
towards the low water line demonstrates clearly, I think, that 
the submergence of the old forest bed is due to the removal of 
the superficial layer, and the encroachment of the sea, and not 
to the subsidence of the land with respect to the level of the 
sea. 
Of course, these remarks refer only to the submerged forest at 
Northam. But there appears to me to be some reason for a re- 
consideration of the subject, whether a subsidence of land around 
our southern seaboard has taken place or not. The submerged 
forests on our coasts are numerous, and lands corresponding 
with these have existed within the period of history or tradition, 
and in some places, as in Torbay and Penzance, within the 
