98 DISCOVERY REPORTS 



to be found. At several points the rocks are clearly stratified, showing three or more horizontal layers of dark grey 

 rock separated by narrow bands of red tuff. Sometimes yellow tuff with red inclusions was to be seen and frequently 

 the rocks were much contorted and intersected by dykes. At the north-eastern corner of the island are low cliffs 

 formed of a light grey rock, perhaps volcanic ash. {South Sandwich Islands Memoir, p. 175.) 



Capt. Larsen landed at the south-eastern corner and mentions a crater here, as well as at the 

 north-eastern point of the island. Biickstrom ((i), p. 175) described the rocks collected as rather 

 uniform types of vesicular olivine-basalts in which phenocrysts of olivine, augite, and plagioclase 

 (Ansa) predominate over the ground-mass. The ground-mass consists of small granules of pyroxene, 

 laths of plagioclase, and some magnetite. The resemblance of these rocks to the olivine-basalt of 

 Saunders Island (p. 97) is obvious. 



Bristol Island (South Sandwich Islands Memoir, pp. 176-8). Bristol Island is an irregular oval in 

 shape and has a circumference of 14 miles. The highest point is Mt Darnley (3600 ft.). Its profile 

 seen from the north has the shape of a horse-shoe, and is conjectured to represent part of the rim of 

 a crater. Bristol Island is heavily glaciated and the Discovery II party were satisfied that all volcanic 

 activity had ceased. Three rocky islets, Grindle Rock, Wilson Rock, and Freezeland Peak, stand in 

 line off the western coast of the island. 



Capt. Larsen landed on the north-eastern side of the island^ and collected some rock specimens. 

 Biickstrom ((i), pp. 175-6) describes them as of reddish grey tints, and as showing numerous small 

 crystals of feldspar. In thin section numerous micro-phenocrysts of zonal plagioclase are disclosed, 

 of composition An75_85 . Pyroxene is confined mainly to the ground-mass and belongs to the enstatite- 

 augite series. Olivine is only sparingly present. A photomicrograph of this andesitic basalt type is 

 given by Backstrom ((i), fig. 20, p. 176). It conforms closely to the main type of lava erupted from the 

 South Sandwich Islands volcanoes. 



Although no landing was made, the geological observations made by the Discovery II party (South 

 Sandwich Islands Memoir, p. 177) are important and must be quoted in full: 



The rocks on Bristol are similar to those on the other islands. At Fryer Point black basaltic lava is to be seen and 

 the rock exposures on the bluff on the south side, at the western headland and in other parts, are of yellowish and 

 red tuff, or tuff conglomerate, sometimes stratified with a grey rock interposed between the layers, but frequently 

 much contorted and with many intrusive dykes. 



From a geological point of view the three large outlying rocks appear to be more interesting than any other place 

 in the entire group of islands. . . . The great pillar on Freezeland is composed of a pale brown rock of a kind not seen 

 elsewhere. It showed distinct signs of bedding and in the upper part of the column some broad reddish bands. 

 We believe this may be a sedimentary rock. The eastern part of Freezeland, forming the lesser of the two summits, 

 is different ; it is formed of a brownish rock, with vertical fissures and striation, and may be metamorphic. Wilson 

 Rock, nearer the mainland, is a vast mass of black columnar basalt, while Grindle Rock repeats the reddish and 

 yellowish tuff's seen on the adjacent headland of the island. Thus, if our conjectures are correct, the whole succession 

 of rock formations in the Sandwich group is to be found in these three islets. Freezeland shows the only likely exposure 

 of the underlying sedimentary series that we know to exist, Wilson is of the overlying basalt, here seen in far greater 

 thickness than elsewhere, while Grindle is formed of the superposed tuffs which are characteristic of all the islands 

 of the group. 



Among the material from the South Sandwich Islands submitted to the author there were specimens 

 from near Bristol Island. One of these was a bag of scoria and lapilli dredged from St. 370 at a point 

 two miles north-east of Bristol Island, and a bag of small stones, including lapilli, which were picked 

 off a piece of floating ice near the island. 



A thin section of the dredged scoria from St. 370 shows that it is a sponge of opaque black glass 

 with minute microlites of feldspar and augite, and a few micro-phenocrysts of plagioclase (Augo) 



' The position of the landing-place is mentioned in Biickstrom's memoir ((1), p. 175). Cf. South Sandwich Islands 

 Memoir, p. 178. 



