THE GLACIAL PERIOD. 



223 



this remarkable accumulation are more readily explained and 

 accounted for by a glacial hypothesis than by any other view of 

 their origin. The overlying sands with flints betray the action 

 of water ; the flints are all more or less altered and discoloured, 

 and their sharp angles have been removed. They are often 

 indeed rounded. The deposit, according to Cossigny, is the 

 result of torrential action. It is covered in turn by another 

 sand-bed of much the same composition, but which contains 

 here and there boulders of a Tertiary quartzose conglomerate, 

 similar boulders being sprinkled over its surface. The position 

 of this last bed shows that it was not laid down until after the 

 other deposits had been much denuded,' — until, in short, the 

 surface had attained its present configuration. M. de Cossigny, 

 as I have said, relegates all these deposits to the Tertiary Period, 

 but the evidence upon which he relies is perhaps hardly conclu- 

 sive. But whatever their age may be, it is certainly very 

 remarkable to meet with accumulations of such a character in 

 the low-lying regions to the south of Paris. Cossigny is of 

 opinion that the glaciating agent, if such it were, must have 

 come from the north, since there are no mountains or high- 

 grounds in the neighbourhood of Paris from which glaciers 

 could have flowed. But mountains are not necessary to the 

 formation of an ice- sheet, neither are we compelled to infer that 

 the ice was continuous with any great northern mer de glace. 

 During a period of extreme glacial conditions it is probable that 

 wide regions in the low grounds would be covered with massive 

 sheets of snow and n&o6 passing into glacier-ice, which would 

 have a motion of their own. The dissolution of these local ice- 

 sheets would give rise to more or less copious floods and tor- 

 rents, to which we might attribute the origin of the sand with 

 flints that overlies the older morainic accumulation. The more 

 recent sand with erratics of conglomerate may pertain to some 

 long subsequent epoch when fluvio-glacial conditions returned. 1 



1 For accounts of these and similar accumulations, see Laugel : Bull. Soc. G60I. 

 France, 2 e Ser. t. xvii. p. 316 ; Ibid., 2 e Ser. t. xix. p. 153 ; Ebray : Ibid., 2 e Ser. t. 

 xvii. p. 695 ; Hebert : Ibid., 2 e Ser. t. xix. p. 445 ; Ibid., 2 e Ser. t. xxi. p. 58 ; De 

 Mercey : Ibid., 3 e Ser. t. i. pp. 134, 193 ; De Cossigny : Ibid., 3 e Ser. t. iv. pp. 230 



