UPTHRUST MARINE MUDS 275 



visit to Hut Point in November 1908. These balls were about half an inch in 

 diameter, and for some time were supposed to be derived in the same way as the 

 feathery balls which occurred as the excreta of Skua Gulls that had been feeding on 

 penguins. The discovery of the sponge spicule raised beach deposit near Cape 

 Barne, however, led to a closer examination of these balls being made, when they 

 were found to consist of the spicules of siliceous sponges. There is no north wind 

 blowing in this district with sufficient strength to convey these sponge spicules to 

 Hut Point. It seems probable, therefore, that there is a deposit here of sponge 

 spicules analogous to that of Cape Barne. This, too, is perhaps upthrust moraine. 



SUMMARY 



In regard to the question as to whether there are true raised beaches indicating 

 negative movement of the ocean, or positive movement of the land to the vertical 

 extent of their present elevation above sea-level, or whether they are upthrust 

 moraines analogous to those of Spitzbergen, has not yet been indisputably settled. 

 At the same time the preponderance of evidence appears to be greatly in favour, in 

 the case of most of them at all events, of their being of the nature of upthrust 

 moraines. In our paper to the International Geological Congress in Stockholm in 

 1910 we inclined to the opinion that these deposits were genuine "raised beaches," 

 chiefly for the following reasons : — 



1 . At Cape Barne there was no evidence of comminution of the shells or striation , 

 the valves being mostly double and hinged together. The same feature was noticed 

 at the Dry Valley deposits, where the shells were almost exclusively composed of 

 the very fragile variety Pecten Colhecki. It was also observed that at the Backstairs 

 Passage deposit near Mount Larsen a large boulder of gi-anite was encrusted with 

 a huge and very fragile siliceous sponge, obviously in position of growth. 



2. In the case of two of the deposits, viz. that of Cape Barne and that at Backdoor 

 Bay, they are both at almost exactly the same elevation, viz. about 160 feet above 

 the sea. This is of course suggestive of a continuous water-level at that horizon. 



3. There is evidence near Cape Bird, at Backdoor Bay, and on the seaward 

 face of Mount Crummer, of marked terracing. The terrace at Backdoor Bay was, 

 however, quite devoid of any trace of marine organisms as far as we were able to 

 ascertain. We had no opportunity for searching the terraces at Cape Bird or at 

 Mount Crummer. It is possible that there these terraces are rather of the nature of 

 parallel roads, and may have been formed by wave action in supra-glacial lakes on the 

 surface of the former tongue of the Great Ice Barrier when it filled McMurdo Sound. 

 Such an opinion will hardly apply to the Mount Crummer phenomena ; but these are 

 much less clearly marked than are the terraces of Cape Bird and Backdoor Bay. 



Evidence for the true " raised beach " character of the deposits, when critically 

 reviewed in the light of modern discoveries at Spitzbergen, does not seem strong. 



