56 D. Ferguson — Geology of South Georgia. 



The three divisions may be collectively 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 

 unconformability, we have named the Cape George Harbour Series. 



Cnmlerland Bay Series. — The upper, middle, and lower divisions 

 of this series include all the stratified rocks of Eoyal Bay, New- 

 Fortune Bay, part of Cape George Harbour, and much the largest 

 part of Cumberland Bay, the whole of Stromness Bay, Possession Bay, 

 and on to the north-western extremity of the island at Bird Island. 

 It also includes the stratified rocks from Bird Island and Cape 

 Weddell along the south-west coast to Annenkov Island and 

 ]!^ovosilski Bay. 



The Upper Division of the Cumberland Bay Series. — The upper beds 

 of the upper division have a creamy-white colour, whicli easily 

 differentiates them from the middle and lower divisions of the series. 

 These are succeeded by blue and purplish -coloured shales, which 

 continue down to the upper beds of the middle division, which are 

 whitish, and gradually change to a characteristic reddish-brown 

 colour. 



The rocks of this division when freshly fractured are of a grey 

 colour, and but little different in texture or composition from those of 

 the reddish-brown middle division underlying them. They are crystal- 

 tuffs, grey grits, fine-grained greywacke, and slaty shales. They are 

 in some cases coarser than the rocks of the two lower divisions, and 

 the dark or black shales, strongly evident in the lower division and 

 frequently seen in the middle division of the series, are only meagrely, 

 if at all, present in the upper division. 



The total thickness of the upper division can only be estimated 

 provisionally at 1,500 feet. There are no higher horizons seen on the 

 island, and consequently it is a denuded upper surface of the upper 

 division that is exposed. 



The upper division is well developed on Bird Island on the north- 

 western extremity of the coast, and at Cape Weddell and Adventure 

 Bay. It extends pretty generally as a fringe along the southern 

 coast, including Cape Demidov and Cape Nunez, and on to Novosilski 

 Bay. Annenkov Island is mainly formed of it, and so also is Cooper 

 Island, off the south-eastern coast. 



The Middle Division of the Cumherland Bay Series. — The middle 

 division is easily distinguished by the reddish-brown colour of the 

 rock exposures composing it. The colour is superficial, as the rocks 

 are generally of a grey colour when freshly fractured. 



The rocks of the middle division are more or less indurated, due 

 to folding movements. They are higlily siliceous, and while some 

 of them are fine-grained others are gritty. There are still coarser 

 sediments, which may be regarded as fine conglomerates, with very 

 small rounded pebbles. Interbedded with them are black shales, not 

 of great thickness in any one bed. The crystal-tuffs also occur in 

 some quantity. 



The thickness of the middle division cannot be less than 3,000 feet, 

 and may be much greater. 



