608 Transactions. 



The extent of a marine ice-sheet would seem to be mainly dependent 

 on the degree of refrigeration. It is difficult to see where the depth of 

 the sea comes in when once the ice is afloat, except it be supposed that 

 the ice can only advance where it rests on the sea-floor. But Eoss, Scott, 

 and others have shown the fallacy of this contention, proving by soundings 

 that the Antarctic ice barrier in Ross Sea is afloat, as stated above, for 

 many hundreds of miles. 



Dr. Marshall* further objects that no boulders foreign to New Zealand 

 have been found in any glacial deposit. In making this statement Dr. 

 Marshall must surely have failed to recognise the fact that the movement 

 of the ice in the New Zealand area would everywhere be away from the 

 centre of movement, at the main divide, towards the sea. I never sug- 

 gested that the Antarctic ice advanced to New Zealand and crept over its 

 highlands and mountains. Polar ice cannot disregard the laws of gravita- 

 tion. Ice obeys all the laws of motion of a viscous fluid, and hence flows 

 away from the gathering-ground to a lower level like a slowly moving 

 river. Obviously, as the New Zealand land-ice alone flowed over Otago, 

 it would be futile to look for Antarctic boulders in the local moraines, as 

 the pressure of the land-ice would certainly keep the Antarctic sea-ice away 

 from our shores. 



The local origin of morainic drift, or till, is emphasized by all writers 

 of text-books on geology. Thus Sir Archibald Geikie,f in his text-book, 

 says, " The great majority of stones in boulder-clay are of local origin, not 

 always from the immediate adjacent rocks, but from points within a dis- 

 tance of a few miles." Further on he says,} " No Scandinavian blocks 

 have been met with in Scotland, for the Scottish ice was massive enough 

 to move out into the basin of the North Sea until it met the northern ice- 

 sheet streaming down from Scandinavia, which was kept from reaching 

 the more northerly parts of England." 



Again, he says, on the authority of Professor Salisbury, that the general 

 local character of the glacial drift is as marked in Canada and the 

 United States as in Europe. 



In other words, blocks can only be carried from their gathering-ground, 

 or centre of movement, within the limits of flow of the ice-stream, and in 

 all cases the pressure of land-ice will be superior to that of ice supported 

 on water. 



Boulder-clays or till, and all infraglacial drifts, must from their mode 

 of formation be composed of rocks of local origin. On the other hand, 

 the rocky material borne on the back of the glacier or interbedded in an 

 ice-sheet may be carried a great distance from the parent rock. 



British geologists recognise two distinct epochs of glaciation in the late 

 Tertiary, separated by an interglacial period of milder climatic conditions 

 — namely, an older epoch during which Scotland and the greater part of 

 England were covered with an ice-sheet, and a later epoch of less intense 

 refrigeration than the first, as shown by the more local character of the 

 glaciation. The last was distinguished by many minor phases of intensity. 



As far back as 1876 Captain Hutton§ also distinguished two epochs of 

 glaciation in the late Tertiary in New Zealand. To the older, or period of 



* P. Marshall, Otago Daily Times, 13th May, 1C09. 



t Sir Archibald Geikie, " Text-book of Geology," vol. ii, p. 1310. 



X L.C., p. 1311. 



§ F. W. Hutton, " Geology of Otago," 1876, pp. 62-67. 



