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XXIV. — The Geological Relations and Some Fossils of South Georgia.* 

 By J. W. Gregory, D.Sc, F.R.S. 



(MS. received March 2, 1914. Read July 6, 1914. Issued separately May 20, 1915.) 



[Plates XCII-XCIIL] 



The special interest of South Georgia depends on its evidence regarding the geology 

 of the part of the Southern Ocean which lies south of the South Atlantic. According 

 to Professor Suess, the island is an extension of the Andes, which, at the southern 

 end of South America, turn eastward, and by a great horse-shoe-shaped curve pass 

 through South Georgia to the South Orkneys and Graham Land. 



The geology of South Georgia is but little known. Thurach t described the island 

 as consisting of metamorphio rocks, ranging from granular gneiss to clay-slate, and 

 of diabase tuff. He collected a pebble of granular gneiss, and a " phyllite-gneiss " 

 containing tourmaline, apatite, iron-ores, and andalusite ; also specimens of various 

 phyllites and clay-slates, and interbedded granular limestones, calc-phyllites, and 

 quartzites. According to Thurach there is a complete passage from the phyllitic- 

 gneiss to the slates,} and his illustrations § show that the rocks are very crushed 

 and crumpled. The diabases and tuffs recorded by Thurach suggested that South 

 Georgia had been an active volcanic centre. Gunnar Andersson identified some 

 of its igneous rocks as porphyrite, a fact in favour of South Georgia belonging to 

 the Andean line. Thurach obtained no evidence as to the age of the rocks ; the 

 first fossil from the island was obtained by the Swedish Expedition at Cumberland 

 Bay, and Dr Otto Nordenskjold kindly tells me that it has been identified as 

 a Posidonomya and as probably Mesozoic. This conclusion recalls Darwin's view 

 of the Cretaceous age of the clay-slates of Tierra del Fuego. 



Dr Konig, of the German Antarctic Expedition under Lieut. Filchner, found 

 a poorly preserved fossil. It has been submitted by Professor Salomon to Professor 

 Pompeck.i, who says that it may be an Acanthoceras and may be " Kreide " in age. 

 Professor Salomon kindly lent me this specimen, and its matrix agrees closely with 

 rocks collected from the same locality by Mr Ferguson ; they come from the middle 

 part of the Cumberland Bay Series and are largely composed of volcanic debris. 



The preliminary paper in which Dr Heim || announced the discovery of this fossil 



* A preliminary note on the evidence of these fossils was published in the Geol. Mag., Dec. 6, vol. i, 1914, 

 pp. 61-64. 



t H. Thurach, " Geognostische Beschreibung der Insel Sud-Georgien," Internat. Folar/orschung 1882-83: 

 Die deut. Exped., vol. ii, 1890, No. 7, pp. 109-166. 



+ Ibid., p. 131. § Ibid., pp. 154, 157, 15S. 



|| F. Heim, "Geologische Beobachtungen iiber Sud-Georgien," Zeit. Ges. Erdk, Berlin, 1912 (No. 6), pp. 451-456. 



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