some of the larger stones at the top of the tin ground and to the stumps of the oaks.
Then comes a stratum of dark silt, about 12 inches thick, with decomposed vegetable matter, and on this a layer of leaves of trees, hazel nuts, sticks and moss for 6 or 12 inches more. This layer of vegetable matter is about 30 feet below the level of the sea at low-water and about 48 feet at spring tides. It extends with some interruption across the valley.
The point is not made quite clear in Colenso's account, but apparently there is no marine deposit between the "tin ground" and the peat, the oyster-bed above mentioned representing the base of bed c, which at that point has cut through the peat, so as to lay bare part of the gravel and some of the oak- stumps rooted in it. So far, wherever we have a carefully noted section of the lowest deposits in these valleys, the tin ground or the gravels are directly succeeded by a growth of oak trees. It looks as though the climate ameliorated, the more violent floods ceased, and an oak forest grew across the alluvial flats, without there being any, or much, change of sea-level.
(c) Above the vegetable matter and leaves (b) was found a "stratum of sludge or silt" 10 feet in thickness. It showed little variation except from a brownish to a lead colour. "The whole is sprinkled with recent shells, together with wood, hazel nuts,
