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118 the Neolithic period, and of the rate at which changes of the sea-level can take place.

The first point to be considered is the length of time occupied by the growth of the series of submerged forests. On first examining, or reading accounts of, deposits of this sort one obtains a vague impression of long periods, during which mighty oaks flourished. Both the movements of submergence and the intervening periods of vegetable growth seem to require great lapses of time. On closer study, however, the evidence seems scarcely to support this view, for estuarine silts are deposits of exceptionally rapid growth, and one finds that the usual characteristic of a "submerged forest" is that it shows indications of only a single generation of trees. The trees also are usually small, except where the submerged forest rests directly on deposits of much earlier date, or on solid rock.

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