﻿1851. J 



AUSTEN ON THE PLEISTOCENE PERIOD. 



135 



In the English Channel area, as we have seen, there are evidences 

 of two distinct levels, as compared with that of the sea at present : 

 the most recent, or that which formed the vertical coast line (c, fig. 1) ; 

 the other, or that of the high-level sands, shells, and shingle. This 

 last I would refer to the period of the greatest depression of the 

 northern portion of the British Islands during the pleistocene oscil- 

 lations. This movement, which commenced on the north and extended 

 progressively southwards, was one to which certain areas in the south 

 of these islands, dependent on E. and W. axes, were not altogether 

 insensible. These areas, as I have shown (Quart. Journ. Geol. Soc. 

 vol. vi. p. 91), formed a range of insulated lands during the whole 

 of that period, and seem as it were to have been the hinge-line of 

 that remarkable depression. That movement, which affected this 

 line itself, was the latest in point of time, and the least in amount ; 

 and it was then, whilst the whole Northern hemisphere was one wide 

 expanse of sea from the line of N.L. 51°, that the true whales, whose 

 presence is so constant in the higher marine accumulations of the 

 Channel (Pentuan, Plymouth, Ouze, Wye, Somme, &c), ranged 

 freely into these regions. The low temperature of this region, then, 

 was the result of the wide extent of the Northern Ocean. 



We obtain a measure of the low temperature of this period of 

 greatest depression. Coast ice must have formed, occasionally at 

 least, as low down as around the E. and W. line of unsubmerged 

 land, as we can imagine no other means for transporting the large 

 rocks of sandstones which occur in the deep shingle on the north of 

 the Wealden area (see Quart. Journ. Geol. Soc. vol. vi. p. 89). Mr. 

 Nicol has called attention (Quart. Journ. Geol. Soc. vol. v. p. 20) to 

 the curious fact that the pleistocene mud of the Valley of trie Clyde 

 contains imbedded angular patches of sand. The explanation I believe 

 to be this : on the breaking up of the coast ice, portions of the mar- 

 ginal zone of sand, also frozen, would be floated away with the blocks 

 of ice ; as the upper surfaces of these thawed, the lower and charged 

 portion would sink ; and if this happened over a sea bed of soft mud, 

 they would bury themselves, and, being imbedded in the till, would 

 preserve their angular forms when the particles of sand were no longer 

 held together by ice. 



These depressed latitudes again rose into the condition of dry land, 

 of which the extension was much greater than that of our present 

 limits, and included large portions of our surrounding seas. The di- 

 stinctive features of this period — the passage from pleistocene to pre- 

 sent conditions — though one upon which much has been written, is 

 still one on which very much remains to be done, and which, ii 

 attempted here, would require more space than could be well aflowed. 



By the accompanying table I have endeavoured to obviate the detail 

 and repetition of many known facts, which would have been necessary 

 had I attempted to describe those changes and deposits which in 

 adjoining areas I consider, to be generally synchronous with those of 

 the English Channel. It shows — 



That several areas have continued as dry land from times anterior 

 to the oldest Crag deposits. 



