276 SUPERFICIAL DEPOSITS 



The following features may be emphasized in favour of the theory that the deposits 

 result from glacial upthrust : — 



(a) At least three of the five deposits between Mount Larsen and Hut Point 

 rest on a foundation of glacier ice, just as do the push moraines of Cora Island in 

 advance of the Sefstrom Glacier. 



(b) In at least one of these deposits, that of Backdoor Bay, the marine organisms 

 have obviously been much comminuted and fractured, and the deposit is extremely 

 peaty. The same remark applies, though in a less degree, to the deposit at Back- 

 stairs Passage near Mount Larsen. 



(c) The latitude above sea-level of each of the deposits is variable, ranging from 

 20 feet in the case of the Backstairs Passage deposit, to 160 feet in the case of the 

 Cape Barne and Backdoor Bay deposits, the last two being the only two which show 

 any agreement in level. 



(c^) The following aj^pears one of the strongest arguments : the bathymetric 

 aspect of the organic remains in the Cape Barne deposit, as well as in the Backstairs 

 Passage deposit, jiroves that these organisms lived originally at a far greater depth 

 (some 600 to 760 feet below sea-level) than is suggested by their present height 

 above the sea. If, as Messrs. Chapman and Hedley hold, the Cape Barne and 

 Backstairs Passage deposits were formed at from 600 to 760 feet below sea-level, 

 it is obvious that an elevation of land or general depression of sea-level by an 

 amount of from 20 up to 160 feet would be quite incompetent to raise such de- 

 posits above sea-level. It seems then that the only agent which may reasonably be 

 assumed to be capable of explaining such a work is glacier ice. 



(e) There is conclusive evidence to show that in quite recent geological time the 

 whole of McMurdo Sound has actually been occupied by a thick tongue of the former 

 Ross Barrier when at its maximum extension. It can be proved from the height to 

 which this tongue once rose (moraines around the foothills of Mount Erebus ascend 

 to fully 1000 feet above the present sea-level) that it must have pressed hard even 

 on the deepest portions of the floor of McMurdo Sound. Such masses of glacier ice, 

 moving thus with great force and weight over the sea floor, must surely have pro- 

 duced large upthrusting of the displaced marine sediments in the Antarctic, just 

 as has been proved to be the case in the Arctic. 



We, therefore, wish now to withdraw our previous views as expressed in the 

 paper read before the International Geological Congi-ess at Stockholm in 1910 as to 

 the true "raised beach" character of the above deposits in favour of the view that 

 they are of the nature of upthrust moraine, except probably in the case of the Dry 

 Valley deposit of Pecten Colbecki. 



