The submerged forests seen on the foreshore in western Cornwall are so like those exposed elsewhere that there is no need for a full description, were it not that they have become so connected with ancient legends of Lost Lyonesse, a country which is supposed to have joined the Land’s End to the Isles of Scilly somewhere about the date of King Arthur and Merlin. To what extent these stories are due to observation of the submerged forests and of the rapid waste of land in Mount’s Bay, supplemented by a vivid Celtic imagination, which saw “the tops of houses through the clear water,” is doubtful. Legend may assist, as is shown in a later chapter (p. 120). One thing is clear, the alluvial flat of Mount’s Bay, under which the submerged forest lies, formerly extended much further seaward; and old writers mention the tradition that St Michael’s Mount formerly rose as an isolated rock in a wood. As far as can be calculated from its known rate of encroachment, the sea cannot have reached the Mount till long after the Roman period, and the legend is probably quite accurate. The Mount was surrounded by a wide marshy flat covered with alders and willows till well within the historic period; the contradictory story, that the Phoenician traded to St Michael’s Mount for tin seems to be the invention of a sixteenth-century antiquary.
In Mount’s Bay there has been subsidence as well as loss of land through the attacks of the sea, for beneath the alluvial plain, part of which is still seen in Marazion Marsh, is buried a submerged forest. Stumps of large oaks, as well as roots of hazel and sallow, are to be seen at various points on the foreshore, where the overlying alluvium and peat have been cleared away by the sea. But the oak-stumps seem to be rooted on a soil resting directly on solid rock; they do not appear to be underlain by estuarine deposits, or by lower submerged forests. This particular land-surface may therefore represent a long period of gradual sinking, during which the trees flourished continuously, and first at a considerable elevation above the sea.
The deposit would repay closer examination, for it was not well exposed while I was staying in Cornwall. I could find no trace of man in it at Penzance, and the contained flora was principally noticeable for its poverty and the entire absence of any of the characteristic west-country plants. The trees were the oak, hazel, and sallow, the seeds obtained belong to the lesser spearwort, blackberry, a potentil, self-heal, and some sedges.
Carne, however, in 1846 was more successful at the eastern end of the Bay, for he has handed down to us an account of the strata met with in a mine-shaft on Marazion Marsh. The height of the ground at this spot is only about 12 feet above mean-tide level, and as the deposits penetrated are 32 feet thick, it is clear that both the rocky floor and the lower peat must lie beneath the level of the lowest spring tide. The position of the shaft was close to the Marazion River, where we would expect also to find an ancient buried channel. The upper deposits may be of very modern date. Commencing at the top the succession met with was:—
| Feet | |||
| Slime, gravel and loose ground | 8 | ||
| Recent estuarine deposits | { | Rather soft peat | 4 |
| White sand with cockles | 12 | ||
| Recent or Neolithic | { | Layer of trees, principally oak and hazel, all prostrate. One piece of oak, about 14 feet long, appears to have been wrought, as if it had been intended for the keel of a boat | 1 to 2 |
| “Submerged forest” | { | Hard solid peat, of closer texture than the upper bed | 3 |
| Alluvial gravel with tin-ore | 4 | ||
| Slaty floor | at 32 |
It will be observed that the supposed keel of a boat occurs above the old land-surface, among driftwood which probably belongs to the first infilling of the estuary after the submergence took place. The upper peat is probably nothing but the surface of the modern marsh, smothered and much compressed by the eight feet of “loose ground” or refuse from the neighbouring mines which had accumulated above it. The cockles probably flourished at the same level (about low-water mark) as that at which they are now found.
It is not our intention here to deal in any detail with the submerged land-surfaces noticed on the French coast opposite. The Channel Islands yield indications of submergence, and if its amount was as great as that proved on the north shores of the Channel, then the Channel Islands must have been connected with the mainland up to a period when the climatic conditions were similar to and the fauna and flora resembled those of the adjoining parts of France at the present day.
Further west, recent discoveries on the shores of the Bay of Biscay are of considerable interest, for submerged forests occur at various places, though the maximum amount of the submergence has not yet been satisfactorily made out.
One of the most interesting of the submerged forests seen between tide-marks on the French coast was that discovered a few years since by Monsieur Emil Gadeceau in Belle Ile. This island lies off the mouth of the Loire, and its position some way from the coast and well out in the Atlantic induced him to make a special study of its flora. While engaged in this, his attention was drawn to certain hard peaty deposits seen only at low tide, and he asked me to undertake the examination of the seeds found in them. This work was gladly undertaken, as it carried further south the examination which was then being made into the flora of the submerged forests.
The results were somewhat surprising; out of about 30 species sufficiently well preserved for identification, six were no longer living in Belle Ile, though known in Western France. The whole flora might have come from the north of England, characteristic French species being entirely missing, though this element is fairly represented in the living flora of the island. In short, the flora is a northern one, though in no degree arctic, and in this it agrees well with the poor assemblage commonly found in the submerged forests of the south of England.