of icebergs during this period is found in the associated series, or parts of series, of fossil remains taken from the gravels—as, for instance, at Bishop Stortford, where a good number of vertebræ and other bones of Pliosaurus, parts of the same animal, were discovered. These of course were derived from some of the Secondary rocks to the northward, and must have been transported in a large mass of the matrix in which they had been previously fossilized.
The submergence which began at the commencement of the Lower Glacial series went on until the waters af the North Sea were again united to those of the Atlantic[1], when a strong current was set up in that direction. It steadily continued during the accumulation of the Middle Glacial beds, bringing them up to the level at which they are now found. But while yet the higher ranges of the Chalk were above the water, the lower parts of the escarpment had gone down sufficiently to admit of the passage over them of the sea; and this of course began to give rise to a set of very different physical conditions. In place of the strong southerly current confined to the eastern side of the chalk ridge, the waters having admission to a much larger area, their power (within that area) of transporting gravels was materially lessened, and, as submergence went on, absolutely lost. For this reason the gravels are found running not quite although nearly up to the lower levels of the chalk escarpment.
[The ground to the N. and W. of the escarpment (fig. 2, Pl. XV.) being at even a lower level than where the gravels occur, was of course also under water; it was, however, land-locked on every side but one, and formed a bay in which no current of any extent was possible; consequently we find in it but few (if any) deposits that undoubtedly belong to the Middle Glacial series. The waters from the bay flowed outward through the "Wash" to join the southerly current, and contributed their share of pebbles to the gravel that it deposited.]
It is almost impossible to locally classify in detail these drifts; but, speaking generally, the coarser gravels are found, as might naturally be expected, in positions nearest to the chalk ridge, as in the neighbourhood of Clare, the finer gravels in the intermediate country between it and the most distant deposits at Hertford, where they take the form of brick-earth. Throughout are interspersed masses of current-bedded sand and occasional patches of iceborne clay.
The general absence from these beds of fossil remains may be ac- counted for by the conditions of deposit; they were formed in a strong current, which would be (except, perhaps, at the commencement and end of the period) unfavourable to the existence of animal life, while the remains of any plants or animals that may have come within its sweep would speedily be reduced by attrition, except of course those which were previously fossilized, and all of
- ↑ "England was again joined to the continent during the time that the vegetation of the 'Forest-bed' flourished" (Ramsay, 'Physical Geology,' p. 178).
