It should be remembered that the large oak trees which are often found in the lowest land-surface at any particular place do not necessarily belong to any one special stage of the submergence. These same trees may have grown continuously above tide-marks during several successive stages, until at last the upward creeping water rose sufficiently to reach this part of the forest. The large well-grown oaks seen in Mount’s Bay and various other places are, as far as I have seen, all rooted on ancient gravels, solid rock, or boulder clay, not on beds of silt.
We cannot speak confidently as to the time needed to form each thin layer of vegetable soil, marsh peat, or estuarine silt. On comparing the submerged land-surfaces, however, with similar accumulations formed within known periods, such as marsh soils grown behind ancient embankments, or forest-growth over flats silted up at known dates, we can learn something. No one of the land-surfaces alternating with the silts would necessarily require more than a century or two for its formation. Brushwood and swamp growth are the characteristic features of these deposits, and such growth accumulates and decays very rapidly. Possibly trees of older growth may still be found, but I have not succeeded in discovering a tree more than a century old in any one of the marsh deposits alternating with the estuarine silts. Oaks of three centuries may be observed rooted in the older deposits; but this, as above explained, is another matter.
It is useless to pretend to any exact calculations as to the time needed for the formation of these alternating strata of estuarine silt and marsh-soil; but looking at the whole of the evidence without bias either way, it seems that an allowance of 1000, or at most 1500, years would be ample time to allow. A period of 1500 years may therefore be taken to cover the whole of the changes which took place during the period of gradual submergence.
If this is approximately correct, the date at which the submergence began was only 5000 years ago, or about 3000 B.C. The estimate may have to be modified as we obtain better evidence; but it is as well to realize clearly that we are not dealing with a long period, of great geological antiquity; we are dealing with times when the Egyptian, Babylonian, and Minoan civilizations flourished. Northern Europe was then probably barbarous, and metals had not come into use; but the amber trade of the Baltic was probably in full swing. Rumours of any great disaster, such as the submergence of thousands of square miles and the displacement of large populations might spread far and wide along the trade routes. Is it possible that thus originated some of the stories of the deluge?
We will not now pursue this enquiry; but it is well to bear in mind the probability that here geology, archaeology, and history meet and overlap. Any day one of our submerged forests may yield some article of Egyptian manufacture of known date, such as a scarab, which has passed from hand to hand along the ancient trade routes, till it reached a country still living in the Stone Age, where its only use would be in magic. But it might now serve to give us a definite date for one of these submerged forests. It might happen to have been lost with some of the stone implements, or with one of the human skeletons, apparently belonging to persons drowned, for no trace of a grave is ever mentioned. A find of this sort is no more improbable than the discovery of a useless modern revolver in a bag of stone and bone tools belonging to some Esquimaux far beyond the reach of ordinary civilized races.
In this connexion it might be worth while systematically to dredge the Dogger Bank, in order to see whether any implements made by man can be found there. The alluvial deposits are there so free from stones that if any at all are found in them they may probably show human workmanship. The Dogger Bank may have remained an island long after great part of the bed of the North Sea had been submerged, for the Bank now forms a submerged plateau. It may even have lasted into fairly recent times, the final destruction of the island being due to the planing away of the upper part of the soft alluvial strata through the attacks of the sea and of boring molluscs. Pholas is now actively attacking the hard peat-beds at a depth of more than 10 fathoms, and is rapidly destroying this accumulation of moorlog, wherever the tidal scour is sufficient to lay it bare.
BIBLIOGRAPHY
Brögger, W. C. Om de Senglaciale og Postglaciale Nivåforandringer i Kristianiafeltet (Molluskfaunan). Norges geol. undersögelse. 1900-1.
Colenso, J. W. A Description of Happy-Union Tin Stream-Work at Pentuan. Trans. R. Geol. Soc. Cornwall, vol. IV, 1832, p. 30.
[Godwin-]Austen, R. A. C. On the Valley of the English Channel. Quart. Journ. Geol. Soc. vol. VI, 1849, p. 69.