UPTHRUST MARINE MUDS 269 



phenomena of this region. In Spitzbergen it is generally admitted now that there 



are elevated marine deposits of two distinct modes of origin: (1) True raised 



beaches, due to a negative movement of the ocean's surface or a positive movement 



of the land, or to both. Raised beaches of this kind are found in Spitzbergen up 



to about 430 feet (130 metres) above sea-level. (2) There is a type of elevated 



moraine material consisting partly of shelly muds, partly of moraine, which may be 



described as upthrust moraine and morainic deposits. Those in the neighbourhood 



of the seaward front of the Sefstrom Glacier reach a height above sea-level of from 



70 to 80 feet. The material, partly morainic, partly morainic shelly mud, rests, as 



does that of Backdoor Bay in Antarctica, on a foundation of glacier ice. 



The origin of these Spitzbergen upthrust and push moraines is very clearly 



explained in Lamplugh's paper. Some of the Spitzbergen glaciers, like that of 



Sefstrom, are subject to rapid spasmodic advances succeeded by an epoch of retreat. 



In 1882 the Sefstrom Glacier, with its front 4^ miles in width, pressed rapidly 



forwards over the sea floor of Ekman Bay, ploughing out the material accumulated 



on the sea floor and partly pushing it in front of it, and partly driving it up along 



a series of overthrust planes. After considerable retreat the glacier again advanced 



in 1896 as far across Ekman Bay as Coi-a Island, and once more the process was 



repeated. Subsequently the glacier once more retreated, leaving between its 



terminal front and Cora Island a deep canal of sea water separating it from the 



fractured extremity of the glacier with all its overthrust faults and upthrust 



moraines and marine muds stranded on Cora Island. The marine muds intermixed 



with moraine at Backstairs Passage near Mount Larsen may very likely have had 



a similar mode of origin. It has already been shown in this Memoir that in the 



neighbom-hood of the Drygalski-Larsen-Reeves Piedmont there has been considerable 



bending and fracturing of the ice with an upthrust of diatomaceous material and 



foraminiferal mud. It is now suggested that the whole of the elongated domes of 



marine muds, capped by angular moraine and underlaid by glacier ice, have been 



pushed up from some depth from the adjacent sea bottom by the thrusting force 



exerted by the Larsen Glacier, aided by that of the DrygaLski Ice Barrier Tongue. 



This explanation would satisfactorily account for the remarkable fact, emphasized 



by Mr. F. Chapman, that the foraminifera and ostracods found in this deposit 



belong normally to a depth of about 100 fathoms. As has been stated, the height 



above present sea-level of the deposit falls immensely short of 100 fathoms, as it 



only slightly exceeds 3 fathoms. Mr. C. Hedley has pointed out the same anomaly 



in the case of the important elevated marine deposits discovered by one of us 



(R. E. Priestley) between Cape Barne and Backdoor Bay near Cape Royds. Mr. 



Hedley and Mr. Chapman agi-ee in expressing a similar opinion in regard to this 



so-called raised beach, viz. they think that whereas it is now only about 160 feet 



above sea-level, it was formed in the first case at a depth of about 100 fathoms. 



This beach too, like that of Backstairs Passage, is, partly at any rate, underlaid 



2 M 



