part 2] MODE OE TRANSPORTATION 15 V ICE. 75 



of the Isle of Man and by the President at Flamborough Head 

 appear to be true fragments of contemporaneous sea-bottom. 



He congratulated the Author upon the lucidity of his exposition 

 and the ingenuity of his hypothesis. 



Mr. T. C»OOK remarked that the facts brought forward by the 

 Author were extremely interesting to anyone who had tried to 

 understand the means whereby our own high-level shelly gravels 

 had been transported. 



The very interesting process outlined by the Author was one in 

 which the time-factor seemed to be important. A sheet of floating 

 ice would have to be very thick indeed to raise englacial muds and 

 gravels by this means to the heights at which they were found in 

 the British Isles. It was difficult to believe that so thick an ice- 

 sheet could renew itself in this way rapidly enough and completely 

 enough to have the desired effect. The speaker therefore asked 

 the Author whether he could give any gravitation data that would 

 enable one to form some idea of the time that Mould be involved 

 in the renewal of a thick ice-sheet in the suggested way. 



The speaker pointed out that overthrust action in ice-movement 

 was a proved factor of much importance (Geol. Mag. 1911, p. 47); 

 and the Author seemed not to have allowed for the possibility of 

 this action as a means of elevation of englacial material within 

 a moving ice-sheet. The operation of thrust-action had been 

 abundantly demonstrated in Greenlandian and other ice-sheets, 

 and it seemed permissible, therefore, to infer that gravel could 

 be elevated by this means. During a phase of recession when 

 melting was in progress, the raised gravel would he left as relics, 

 which would be seen in all stages from englacial debris to stranded 

 patches, much as the Author had described. 



Sir Jethro TEALI said that, although certain links in the chain 

 of evidence were necessarily wanting, the Author's theory corre- 

 lated so many of the remarkable facts which had been observed in 

 the neighbourhood of McMurdo Sound — for example, the frequent 

 association of mirabilite with the various organisms — that he was 

 most favourably impressed by it. 



The overthrusting theory was doubtless applicable to certain 

 arras, but it did not furnish a satisfactory explanation of the 

 phenomena upon which the Author had laid special stress. 



The Author, in reply, said that, with regard to the question 

 raised by the President as to a limiting thickness in the growth of 

 sea-ice by freezing, it must he remembered that the conditions in 

 the open sea are quite different from those in a deep hay, where the 

 water is comparatively stagnant. The formation of anchor-ice is 

 unknown in the Antarctic, and is apparently limited to fresh 

 water moving at a rate sufficient to pi event surface-ice from 

 forming. As it is the result of radiation, anchor-ice could in no 

 case form under a thick sheet, and that convenient explanation 

 of the raised muds is denied to us. Its occurrence in the Baltic, 

 as mentioned by Prof. Kendall, is very interesting, and is perhaps 

 to l»c correlated with the fact that the Baltic water has a low 



