■828 



SCIENCE 



[N. S. Vol. XXXI. No. 1 



ientirely detached from the inland iee and 

 afloat. Finally, the Great Barrier, of yet un- 

 known extent, discovered by Sir J. 0. Eoss 

 in 1841. 



Shackleton's discoveries add very materially 

 to the knovm area of the vyonderful Great 

 Barrier. The northern front of this oceanic 

 ice-cap, which formerly extended at least one 

 sixth around the globe on the 76th parallel, 

 now covers forty-two degrees of longitude near 

 the 78th parallel, a sea-frontage of about 470 

 statute miles. Its known projection seaward 

 •exceeds 400 statute miles, as its landward 

 origin was determined by Shackleton to be 

 south of 83° 30' S., while its surface is in 

 '11° 46' S. He estimates its average elevation 

 at 150 feet, and it seems most probable that 

 the Barrier is afloat through the greater part, 

 if not all, of its known extent. It is doubtless 

 an under-estimate to place the superficial area 

 of the Great Barrier at 200,000 square miles. 



Formed as are all ice-caps of neve, the Great 

 Barrier is peculiar in that it has not been 

 subjected to great vertical pressures, and con- 

 sequently has a low specific gravity, as is 

 proved inferentially from a detached tabular 

 anowberg which grounded in water about half 

 its depth or thickness. 



While the Great Barrier is fed only to a 

 very slight degree by the inflowing glaciers, 

 yet its movement seaward is doubtless due to 

 some degree to the impulse given by enormous 

 pressures from the great incoming glaciers of 

 adjacent lands, especially from the mountains 

 of South Victoria Land. For instance there 

 must be a pressure of incalculable but vastly 

 enormous power from Beardmore glacier, 

 which has a surface area of over five thousand 

 square miles, an average thickness of possibly 

 a thousand feet, and necessarily a great 

 velocity of movement due to its average fall 

 of sixty feet to a mile throughout its length 

 of one hundred miles. Some idea of this 

 force may be gathered from the fact that it 

 " raises pressure ridges on the Barrier for 

 twenty miles out from its junction therewith." 



The rate of superficial increase of the Bar- 

 rier from local snowfall, and its rate of sea- 

 ward movement are approximately known 

 through a depot of provisions made on the ice 



in 1902 and uncovered six years and four 

 months later. There had been an increase of 

 98 inches of snow, an average of 15 inches 

 of unmelted snow annually, and an average 

 annual movement seaward of " a little over 

 500 yards a year," about three tenths of a 

 mile. 



It would appear that the portion of the 

 barrier farthest from the sea (over 400 miles) 

 might be twelve hundred years in reaching 

 the open ocean, and could then have acquired 

 a thickness of 1,500 feet, provided it was 

 wasted with normal rapidity. Eoss in 1841 

 and Shackleton in 1908 observed portions of 

 the sea-front where the cliffs rose 250 feet 

 above the open ocean. 



It is apparent that the sea-face of the bar- 

 rier is steadily and rapidly disintegrating, as 

 it has receded more than thirty miles since 

 1841. 



The suggestion that " a great deal of (the 

 inflowing glacier ice) may be thawed off from 

 below by the sea-water " can not be accepted 

 as undoubtedly the ocean has a uniform tem- 

 perature of about 28°. Repeated observations 

 for about three years by the Lady Franklin 

 Bay expedition in the Arctic regions proved 

 that the immersed portions of ice-floes of the 

 northern seas, being fresh-water ice of land 

 origin, are preserved indefinitely. 



Glaciers. — Space fails in which to consider 

 at length the many interesting observations 

 on Antarctic glaciers visited and discovered. 

 The two floating piedmont glaciers, Nordens- 

 kiold and Drygalski barriers, have been else- 

 where mentioned. The former is believed to 

 be " moving actively from inland seawards," 

 and there were 660 fathoms of water along its 

 fifty-foot sea-face eighteen miles from shore. 



The largest known ice-river of the world is 

 the Beardmore Glacier, situated between 83° 

 33' and 85° S., discovered and traversed by 

 Shackleton and his Southern party. It is 

 equally wonderful in its extent, its environ- 

 ment and its rapid movement. 



One hundred miles in length and fifty in 

 width, its surface area approximates 5,000 

 square miles. Through a glacial valley shut 

 in between lofty sandstone mountains, the 

 glacier falls 6,000 feet in its course of 100 



