rocks from the south orkney islands 3s9 



Station 1094: Inaccessible Islands 



The collection from this station is represented by one specimen which is stated to 

 represent the material of the main mass of the islands. 



The specimen is a typical chlorite epidote schist with a few grains of a bluish green 

 hornblende. Clear quartz, part of which represents vein material and turbid albite form 

 the colourless constituents between the main mass of chlorite and epidote. Sphene with 

 cores of rutile forms an accessory constituent. This rock represents a dynamically meta- 

 morphosed basic igneous rock of original doleritic character and may represent a 

 retrogressive stage of a hornblende schist. 



Station 1095: Wilton Bay, Laurie Island 



Rocks collected at this station come from two islets in Wilton Bay and the mainland 

 of Laurie Island (east side of Wilton Bay). 



The rocks from the islets and the mainland consist of grey quartzo-felspathic grits or 

 greywackes which are composed of quartz with strain shadows, abundant sericitized 

 albite, fragments of dense felsite, all angular and packed together with a minimum of 

 siliceous matrix or separated by chloritic shreds and flakes of detrital biotite. Other 

 fragments noted, but less commonly, were grains of microperthite and granophyre. The 

 rocks are much veined by quartz accompanied in one example by prehnite. 



On the "islet 40 ft. high" in Wilton Bay there also occurs a dark grey muscovite- 

 bearing and quartz-veined shale which is reported to occur as a vertical band 4 ft. thick 

 striking east-north-east in the greywackes, 



GENERAL DISCUSSION 



From the foregoing description it would appear that the rock groups recognized from 

 the South Orkneys may be divided into: 



(a) An older metamorphic series coming from Signy Island, south coast of Corona- 

 tion Island, Larsen Island and Sandefjord Bay (west coast of Coronation Island). 



(b) A younger series represented by quartzo-felspathic greywackes and interbedded 

 shales — from Michelsen Island, the south-east corner of Powell Island, Fredriksen 

 Island and Wilton Bay (Laurie Island). With these are associated a group of conglo- 

 merates which in one place are recorded as resting on these greywackes (Michelsen 

 Island). The younger age of the conglomerates is supported by the internal evidence ot 

 the conglomerates which contain in place abundant pebbles of the greywacke and shale 

 fragments. 



The metamorphic series represent a group of altered sediments ranging in composi- 

 tion from a pure carbonate through types representing marls to a dominant argillaceous 

 facies. 



The hornblendic types are characteristic derivatives of marly sediments. One of their 

 distinguishing features is the presence of albite, which must be recognized as recrystal- 

 lized detrital albite of the original sediment. In this specific character and their general 



