D. Ferguson — Geology of South Georgia. 57 



The middle division of the Cumberland Bay Series is extensively 

 developed along the north-east coast of the island. It extends more 

 or less continuously from Cape North to Cape Charlotte on the 

 southern shore of Royal Bay, and extends south-east to the isolated 

 rocks north of Cooper Island, which have been named after Lieutenant 

 Filchner. It forms the crests of the Allardyce llange, and occupies 

 the liigher ground of all the bays and fiords from Cape North to Cape 

 Charlotte. It gives the characteristic reddish-brown colour to the 

 rocks along the north-eastern coast. It extends south-east of Cape 

 Charlotte, and west of Cape North for some distance, gradually 

 disappearing under the rocks of the upper division at Bird Island and 

 Cooper Island. It forms the crests of Mount Paget, the Sugar Loaf, 

 and the Nordenskjold Peak, 8,383, 7,779, and 7,760 feet respectively 

 above sea-level. The bedding of the rocks of the middle division is 

 extremely well marked, and several of the wall-like escarpments on 

 tlie shoulders of Mount Paget -resemble the rock escarpments of 

 Table Mountain at Cape Town. 



The middle division must extend along the south-eastern coast 

 of the island for a great part of its length along the higher ground, 

 eventually disappearing near sea-level under the upper division. 



27ie Loiver Bivuion of the Cumberland Bay Series. — The lower 

 division is formed of dark or black gritty shales and greywackes. 

 Dark or black fissile shales reach a considerable thickness, and 

 collectively they are the predominant body in the division. They 

 alternate with gritty and fine-grained arenaceous shales, and coarser 

 gritty shales which may be regarded as greywacke, with a few 

 crystal-tuffs. There is much felspathic material in rounded and 

 angular grains in the greywacke, and their prevailing grey colour, 

 contrasted with the black of the shales, gives a distinguishing shade 

 to the division. 



The total thickness of the division is not disclosed in any of the 

 exposures seen, as they invariably descend below sea-level, and the 

 full thickness is not seen, but so far as can be judged, the lower 

 beds seen amount to about 1,200 feet. 



The lower division of the Cumberland Bay Series occupies a fringe 

 of the lower ground near sea-level from Royal Bay to Port Gladstone, 

 Possession Bay. In Royal Bay, Cumberland Bay, Stroraness Bay, 

 and Possession Baj% it can be easily seen coming in below the middle 

 division and underlj-ing it conformably. Its base has not been 

 exposed ; the lowest exposures are seen in Royal Bay, where it is 

 permeated with crystalline quartz in a network of veinlets in very 

 fissile black shales. Subsequent to the disposition of secondary quartz, 

 earth-movements have crumpled the beds. 



In the black shales of this division in Moraine Fiord, Cumberland 

 Bay, there is an intrusion of diabase. It was probably intruded 

 during the deposition of the rocks of the middle division, and was 

 contemporaneous with volcanic eruptions Avhich took place when the 

 lower beds of that division were laid down. There is much volcanic 

 debris and tufaceous material in the beds of the middle division, and 

 their red, rusty-brown colour is very probably due to the decom- 

 position of trachytic lavas. 



