58 D. Ferguson — Geology of South Georgia. 



Cape George Harhoiir Series.— The rocks of this series are only 

 seen in Cape George Harbour and in Cumberland Bay. They are 

 separated in both places by a well-marked unconformity from the 

 rocks overlying them. They were probably folded befoi-e the 

 denudation which shaped the old land surface had begun to operate. 



At Cape George Harbour they are overlain unconformably by the 

 middle division of the Cumberland Bay Series. They descend below 

 sea-level in Cape George Harbour and in Cumberland Bay, and do 

 not rise more than 500 feet above it. In the glacier glen to the 

 north-west off Cape George Harbour they are over 500 feet thick. 



Rock Series exposed: Distributiofi. — The total thickness of the 

 various series of stratified rocks is only provisionally estimated. They 

 are not likely to be less than the estimate given here, but may 

 on further investigation exceed it considerably, especially the middle 

 series. Our present estimate is — 



feet 

 Upper Division of Bocks =1,500 ^ 



Middle ,, ,, =3,000 - Cumberland Bay Series. 



Lower ,, ,, =1,200 J 



Unconformability. 

 Greenish-grey siliceous slates = 500 Cape George Harbour Series. 



Total thickness exposed 6,200 



There is such a marked difference between the greenish-grey 

 siliceous slates and the three divisions of rocks above shown, that 

 the unconformability which separates two geological periods probably 

 indicates a considerable break in time. 



Tecto7nc Geology. — The character of the rocks of the South Orkney 

 Islands is strikingly similar to that of the three series which form 

 the main mass of South Georgia. During the examination of South 

 (reorgia the writer obtained, through the courtesy of the Manager of 

 the Falkland Whaling Company, which was operating in the South 

 Orkneys, ten samples of the rocks of Washington Strait, Coronation 

 Island. They are very similar to those of South Georgia, and the 

 similarity was noted by Dr. Harvie Pirie, who saw them in the 

 Geological Department, Glasgow University. Dr. Harvie Pirie was 

 the geologist to the Scotia Antarctic Expedition of Dr. Bruce, and 

 during it studied the geology of the South Orkneys. 



South Georgia is a ridge mainly of stratified rocks, with its 

 longitudinal axis identical with the general strike of the rocks. It 

 has parallel faults on either slope of the ridge, letting down the rocks 

 to the north-east and the south-west. The evidence of faulting is 

 proved by the middle division of the Cumberland Bay Series 

 occupying the crest of Mount Paget with a slight south-westerly dip, 

 while the upper division forms the coastline at sea-level on the 

 southern side of the island, and is seen in a few straggling beds 

 on the northern coast near New Fortune Bay. The rocks, moreover, 

 have been greatly crumpled and contorted. The axis of the present 

 AUardyce Eange, the central framework of South Georgia, is parallel 

 to the general strike of the sedimentary rocks, of which it is mainly 

 formed. 



