SOUTH SANDWICH ISLANDS 95 



Candlemas Group {South Sandwich Islands Memoir, pp. 165-72). This group consists of Candlemas 

 Island itself, and a smaller one to the west which is now called Vindication Island. A full account of 

 the geography and volcanic phenomena is given in the Memoir. A large collection of rock specimens 

 from the southernmost point of Candlemas Island, made by Capt. Larsen, has been described by 

 Backstrom in the following terms ((i), pp. 169-70, translated): 



[The rocks] are mostly reddish and porphyritic with rounded feldspars which sometimes give an almost white 

 colour to the specimens. Under the microscope they are found to be extraordinarily rich in feldspar of composition 

 Ans5, which is zoned with glassy inclusions and shows both albite and pericline twinning. The main pyroxene is 

 hypcrsthene which is often invested by monoclinic pyroxene, but both pyroxenes may occur as independent cr\'stals. 

 The augite shows the usual polysynthetic twinning, which is also seen in the investments around the hypersthenes. 

 Strongly corroded olivine also occurs but is not common. It is mostly altered to a blackish brown dust, but all the 

 other constituents are fresh. In regard to the systematic position of the rocks, their richness in plagioclase suggests 

 that they represent a transition between the basalts and the andesites. It is difficult to assign some of the rocks to 

 either group, but others which are richer in olivine and pyroxenes should be relegated to the basalts. 



Another type has an extremely fine-grained but holocrystalline texture. It is, however, little different to the above 

 in mineral composition. Its plagioclase is lath-shaped not equidimensional, its pyroxene is sharply euhedral, and 

 olivine is absent. 



Fragmental rocks also occur as very fresh, reddish brown, sandy tuffs which consist of lapilli of hazel-nut size. 

 The latter consist of vesicular lavas with a glassy ground-mass full of crystallites, and carrying numerous crystals 

 of plagioclase, augite, and hypersthene. 



It will be seen how closely comparable these lavas and tuffs are to those of Zavodovski Island and 

 Saunders Island (p. 96). 



Members of the Discovery II party were not able to land on Candlemas Island, but they made 

 numerous observations at close range, noting rugged flows of black basaltic lava in the northern 

 plateau often showing columnar structure {South Sandwich Islands Memoir, pi. xvii, fig. 3). Mr F. C. 

 Fraser has also provided an excellent sketch of rock exposures on the east coast {ibid. fig. 12, p. 169) 

 showing what are obviously stratified tuffs and a coarse agglomerate. 



It was found impossible to land on Vindication Island, but the geological structure of the island 

 was well seen in a sheer cliff face on its north-western side. The rocks here consist of irregular masses 

 of red and brown colours, presumably tuffs, cut by dikes of grey rock which run obliquely, vertically, 

 and sometimes horizontally, not infrequently intersecting one another. Two islets, Cook Rock and 

 Trousers Rock, both of which are tunnelled by wave erosion, show horizontal strata of red tuff and 

 hard grey rock. 



Saunders Island {South Sandzvich Islands Memoir, pp. 172-4). Saunders Island, with a circumference 

 of 17 miles, is one of the largest of the group, and is, perhaps, the best known geologically. At its 

 centre is the glaciated but actively volcanic cone of Mt Michael (2640 ft.). The south-eastern part of 

 the island is composed of bare hills (700-800 ft.) apparently consisting of loose ash or volcanic mud, 

 and with several extinct craters. A very fine photograph of a half-section of a crater on the south 

 coast is given in pi. xx, figs. 2 and 3, of the Memoir. The northern part of the island is a low plateau. 

 All the rock exposures show that the basement of the island consists of columnar basalts similar to 

 those of Candlemas and Zavodovski. 



Capt. Larsen landed with difficulty on the south-eastern coast ((i), p. 170), and Backstrom 

 describes the rocks collected here as, in the main, different from the type common in the South 

 Sandwich Islands in being very dense and non-porphyritic. Under the microscope these rocks show 

 a well-developed fluidal structure delineated by the alinement of the minute feldspar laths in the 

 direction of flow. The mineral composition is plagioclase (An^s-gs), almost colourless pyroxene in 

 rounded grains which belongs to the enstatite-augite series, and magnetite. This rock is free from 



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