802 MR D. FERGUSON ON 



The Rocks of South Georgia. 



In a small island rising out of the Atlantic, and remote from any other land area, 

 a volcanic origin may reasonably be expected. The Canary Islands, Madeira, the 

 Azores, CapcVerd, Ascension, St Helena, Tristan da Cunha, and other Atlantic islands 

 are of volcanic origin. South Georgia is a- striking exception. It is a mass of 

 sedimentary rocks. Its coasts are formed of stratified rocks, indurated generally in 

 places occasionally somewhat altered by pressure-metamorphism. 



With the exception of two comparatively small exposures of sedimentary rocks 

 in Cumberland Bay and Cape George Harbour, the stratified rocks belong to one 

 main series, which may be conveniently called the Cumberland Bay Series, and 

 divided into upper, middle, and lower divisions. The older rocks exposed in 

 Cumberland Bay and Cape George Harbour, and separated from the Cumberland Bay 

 Series by a well-defined unconformity, we have named the Cape George Series. 



Cumberland Bay Seines, Upper Division {Creamy-White Rocks). 



These sedimentary deposits overlying, as they do, the rusty-brown rocks, occupy 

 the highest horizon in the island. Though not all creamy white, that colour pre- 

 dominates. There is no apparent break in continuity between this and the middle 

 division or between the middle division and the lower division. The rocks of the 

 upper division show a grey colour on a fresh fracture, but differ little in texture from 

 the underlying brown rocks. The junction is not very clearly defined. Elsie Harbour, 

 on the north-west corner of the island, is situated right on the apparent junction. 

 The rocks on the south-east side are of the rusty-brown division, and on the other 

 side are the bluish or purple-blue shales of Bird Island. The shales which form a 

 considerable part of Bird Island pass up into the creamy-white rocks of the central 

 part of the island. 



The purple-blue shales descend below sea-level at Cape Pariadin, and only the 

 overlying creamy-white rocks are exposed in that promontory. The thickness of the 

 shales cannot be accurately estimated owing to folding, but it may be from 300 to 

 500 feet. The thickness of the creamy-white rocks above may be provisionally put 

 at 1000 feet. The finest exposure of the rocks of this upper division is at Cape 

 Pariadin, where they contain volcanic tuffs. Other good exposures are provided by 

 the escarpments of Cooper Island and the adjacent mainland. Owing to the diffi- 

 culties of landing, no specimen was obtained from Cooper Island. 



The Cumberland Bay Series, Middle Division {Rusty-Brown Rocks). 



The north-west and south-east coast is occupied for a great part of its length by 

 rocks of rusty-brown colour. They form a distinct group which is easily distinguished 

 and is useful as an horizon in locating the positions of the rocks overlying and under- 



