194 W. H. PENNING ON THE PHYSICAL GEOLOGY OF 



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 vertebrae 

 and other bones of Pliosaurus, parts of the same animal, were 

 discovered. These of course were derived from some of the Second- 

 ary 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 *, 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, abso- 

 lutely lost. For this reason the gravels are found running not 

 quite although nearly up to the lower levels of the chalk escarp- 

 ment. 



[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 commence- 

 ment 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 " (Kamsay, ' Physical Geology,' p. 178). 



