390 DISCOVERY REPORTS 



relationships they bear a striking resemblance to rocks from the South Shetlands which 

 lie about 200 miles west of the South Orkneys. 



At Elephant Island in the South Shetlands group the writer has previously recorded 

 a series of marbles and para-amphibolites^ which have a close lithological and meta- 

 morphic relationship with the rocks now described from Signy and Coronation Island. 

 Observational data on the strike and trend of this older metamorphic series of the South 

 Orkneys is meagre and suggests a general east-west trend, and the rocks themselves 

 provide evidence of the link joining the South Orkneys with West Antarctica.^ 



The younger series of greywackes with interbedded shales form a remarkable group 

 of clastic rocks distinguished by the angular character of their components and the 

 abundance of albitic felspar and fragments of felsitic and rhyolitic rocks. The presence 

 of detrital garnet and fragments of vein quartz and quartzose mica schist suggest that 

 these constituents are derived from the waste of the older metamorphic series. These 

 fragments, however, form but a fraction of the greywackes. The occurrence of angular 

 sericitized and twinned albite — unlike the albite of the older metamorphic series — and 

 the igneous pebbles affirm the presence of sodic igneous rocks^ as the prime source of 

 their materials. 



It would appear then that acid and felspathic volcanic and hypabyssal igneous rocks, 

 possibly including tuffs, occur close at hand in the South Orkneys and that they have 

 contributed in great part to the constitution of the greywackes. The constituent frag- 

 ments of the greywackes make clear that the material has not travelled far from its 

 original source. 



The greywackes and conglomerates now described are perhaps to be correlated with 

 the rocks discovered by the Scotia Expedition on Saddle Island, Coronation Island and 

 Laurie Island. The rocks are referred to by Pirie* as greenish greywackes and con- 

 glomerates with some shales. Shales from an islet off the south coast of Laurie Island 

 near Cape Dundas (eastern end of Laurie Island) were found to contain Pleiirograptus 

 and parts of a Phyllocarid crustacean (allied to Discinocaris) and have been referred to 

 an Ordovician age. Pirie records the most common strike of the greywacke series to be 

 north-westerly varying from north-north-west to west-north-west with dips at high 

 angles to north-east or south-west. The observational data of the Discovery Expedition 

 are insufficient to correlate these rocks definitely with the rocks observed by the Scotia 

 Expedition, but it is clear that the conglomerates and greywackes recorded now have 

 much lithological similarity and may therefore tentatively be assigned to the same series. 



^ Quest Report, 1930, Chapter iv. 



■^ References to the available geological literature on the Southern Antilles including South Orkneys 

 are contained in a paper by Wilckens {Der Bogen der Siidlichen Antillen (Antarktis), S.B. niederrhein. 

 Ges. Nat. u. Heilk. naturw., Abt. 193 1 (1932)). 



^ Tyrrell has recorded a spilite pebble from the Scotia Collection. See Trans. Roy. Soc. Edin., L, 

 Pt. IV, 1915, p. 833. 



^ J. H. Harvey Pirie, Proc. Roy. Soc. Edinb., xxv, 1904-5, p. 463. 



