Page:Submerged forests (1913).djvu/70

56 undoubtedly an old land-surface, lying at a depth of 35 feet below Ordnance datum. This old soil contains:—

The examination of these deposits made it perfectly clear that the lowest land-surface represents a true forest-growth, such as could only live at an elevation clear of the highest tides; one tide of brackish water in the year would have sufficed to alter markedly the character of the fauna and flora of the deposit. Dr Strahan, assuming that the range of the tides was the same as at the present day, and noting the present highest level to which the salt- marshes reach, comes to the conclusion that 55 feet at least is the amount of the subsidence. I should be inclined to add a few feet more, in order to keep the oak-roots well clear of the highest tide during a westerly gale. An exceptional gale occurring only once during the lifetime of an oak might bank up the sea water sufficiently to kill the tree, if it grew at a lower elevation.

It may be argued that when the land stood at the higher level the range of the tides was less, and that consequently the amount of the proved