ISLANDS OF THE SOUTHERN OCEAN
South Georgia.—Lat. 54° S. Long. 37° W.
Topography
This island is about 116 miles long by 20 miles wide, with the longer axis lying in a general N.W. and S.E. direction. It has the appearance of an upland dissected by cirque recession and enlargement. The highest peak, Mount Paget, which is an isolated remnant of the upland, is about 8,000 feet high.
TERMINATION OF ROSS GLACIER
SOUTH GEORGIA
8TH MAY, 1922
SHACKLETON-ROWETT EXPEDITION
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The average peaks in the comb ridges are about 2,000 feet, and the average level of the interior would be placed by the writer as about 600 feet above sea level. The glacial valleys run in general across the longer axis and are separated from each other by comb ridges. The majority of the glaciers show signs of withdrawal. At the N.W. end of the island many of the valleys are free of ice altogether.
One interesting investigation was carried out at Royal Bay, where the Ross Glacier comes down to the sea. The position of the foot of the glacier relative to the shore was first measured by the Gauss Expedition of 1882, then again by Nordenskjold in 1902, and then by the members of the Quest in 1922.
These measurements show this interesting fact—that there was an advance of the foot of over 4,000 feet during the period 1882 to 1902, and that now it is back in the position of 1882. It is suggested that this does not indicate any general advance or withdrawal, but rather that the glacier, which is operating, to use an hydraulic term, under a high head is being forced out to sea where the foot is afloat. It will continue to advance until the effect of the rollers on the floating mass of ice overcomes the tensile strength of the ice and it breaks away. If we assume that twenty (20) years represent this period (it may be a multiple of a smaller period), then this gives an advance per year of about two hundred and twenty (220) feet.
Geology
From Cooper Bay to Bird Island the rocks seen by the writer were of sedimentary origin. They are of the nature of grits, tuffs and phyllites. To the east of Cooper Bay the rocks are igneous. The basement is of a basic nature, with flows, at least two in number, over it. Back from Cooper Bay, and just east of the contact with the sediments, there is a small stock of a more acid rock, which has been called a syenite.
A provisional table is here drawn up to show the relative age relations, with the more recent at the top:
| AT LARSEN HARBOUR | |
| Epidosite | } |
| Spilite | } Doleritic dykes cutting these. |
| Gabbro | } |
| NORTH-WEST OF DRYGALSKI FJORD | |
| Quartz diorite stock | Complex system of dykes. |
| Gabbro | |
Photo: Wilkins
BOOBY WITH CHICK ON ST. PAUL’S ROCKS
Photo: Wilkins
A BOOBY CHICK ON ST. PAUL’S ROCKS
Photo: Wilkins
TYPES OF FISH CAUGHT IN THE LAGOON AT ST. PAUL’S ROCKS
Photo: Wilkins
WHITE-CAPPED NODDIES AT ST. PAUL’S ROCKS
Tectonic Movements
The sedimentary rocks have been subject to considerable folding and faulting. From the direction of the folds and the general trend of the line of schistosity it would appear that the pressure had come from the S.S.W. or N.N.E.
Age
A few fossils of a very indefinite character were obtained, and are now being worked out.[16] Provisionally it may be said that one, a fossil plant probably of the Araucaria type, points to an age not older than lower carboniferous.
Elephant Island.—Lat. 61° S. Long. 55° W.
This is one of the easterly islands in the Powell group of the South Shetlands, and was only landed on at two points, Lookout Harbour and Minstrel Bay.
Topography
The features of Elephant Island probably are similar to what those of South Georgia were before the intense glacial erosion sculptured the island as already described.
POWELL GROUP
SOUTH SHETLANDS
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It is a plateau 300 feet at the rim, but rising gently towards the interior. It appeared to be covered by an ice sheet, and the same may be said of Clarence Island, which lies a few miles to the eastward; only in the latter case there was a definite cliff of ice visible above the rock face.
The glaciers were more of the hanging than of the valley type. Especially was this so on the west coast.
Geology
The rock specimens collected and the little mapping which was done indicate that the island is composed mostly of sedimentary rocks which have been much metamorphosed. Phyllites predominated, but various schists, slates and banded limestones were also seen.
Zavodovski.—Lat. 56° S. Long. 27° W.
This island, the most northerly in the South Sandwich group, was not landed on by the members of the Quest, and the following observations from the ship must be considered only probable and in no way certain.
The island is of volcanic origin, rising as a cone from the sea. The upper levels were not seen by us, but the height of the summit is given by Bellingshausen as 1,200 feet. The cliff rises vertically from the sea about 40 feet, and then there is a long, gentle slope gradually getting steeper.
The lava flows seen on the cliff face appeared to consist of a compact columnar basalt at the base. Above there was a line of red cinder, and above this again what looked to be rough pahoehoe lava. A number of clefts and vents were seen on the face of the cliff, and from these there issued bluish fumes.
Soundings with the Kelvin were taken every half-mile or so, and the material collected corresponds with the basalts and cinder mentioned.
It was unfortunate that we were unable to visit the other islands in this group, for with the exception of the scanty reports of Bellingshausen, C. A. Larsen and a German expedition, the geology and natural history are practically unknown, and the existing charts are not by any means complete.
PETROLOGICAL REPORT, by W. Campbell Smith, M.C., M.A., British Museum of Natural History.
Rock fragments washed from material dredged at 19 fathoms off Zavodovski, South Sandwich group, 20/1/22.
The sample consisted of a few grammes of rounded black pellets varying in diameter from 1 to 5 mm. They consisted of the following:
Ten dense black glassy basalts. All appear free of olivine. Some are crowded with minute laths of plagioclase; others contain fewer minute laths but show a few small phenocrysts of plagioclase, or of augite, or both.
Four dense dark-brown glassy olivine-basalts, some containing many crystals of plagioclase, and a few crystals of olivine and augite. The glass is crowded densely with magnetite and sometimes with other undetermined microliths.
Four rather paler basalts with holocrystalline-porphyritic texture. These contain very small phenocrysts of plagioclase and sometimes of augite, in a ground mass of very minute laths of felspar and grains of augite and magnetite. The texture of the ground mass is intergranular. One of the specimens contained no augite phenocrysts, but rather numerous microphenocrysts of magnetite.
Two small fragments of pale basalt-glass, deep olive-buff in colour. Microliths are absent in one specimen, but they are abundant in the other and consist of small laths of plagioclase, and minute prisms of augite and a few crystals of what is probably olivine. The felspar laths gave extinction angles of 15°, but only a very few measurements could be made. This material resembles the pale patches of glass in the palagonite tuffs of Sicily and of Kerguelen Land,[17] and a somewhat similar though darker coloured rock has been described from Schwartzenfels Hesse as vitrophyric basalt, and has been elegantly figured by Berwerth.[18]