76 DISCOVERY REPORTS 



of a quartz-porphyry formation which has undergone intense cataclastic deformation in Adelaide 

 Island. This formation, which is of Mesozoic age (older than Upper Cretaceous) in Patagonia, and 

 extends in that country over a belt more than 400 km. in length, is thus shown to continue in Graham 

 Land to a further distance of about 1000 km. 



The evidence of this rock collection thus strongly reinforces the conclusion the writer came to in 

 an earlier study, namely, that ' the Graham Land eruptives are identical down to the smallest chemical 

 and mineralogical details with Andean types as far as we know them. The chemical and petrological 

 similarities are so great that one can have no hesitation in subscribing to Nordenskjold's view that 

 the Graham Land ranges, and those of the contiguous islands, are the continuations in Antarctica of 



the Patagonian chains In Nordenskjold's expressive phrase, Graham Land is a mirror-image of 



the southern end of South America. '^ 



PART III. 



PETROGRAPHY OF ROCKS FROM THE ELEPHANT 

 AND CLARENCE GROUP 



6130 



Minstrel , 

 Bat/ 



Cornwallis I 



SIS 



'C Lookout- 



^i 





^^'^ 



■c'O'Brien I 



Clarence I.. 



The Elephant and Clarence Group of islands, comprising Elephant Island, Cornwallis Island, and 

 Clarence Island, in its northern section, and Gibbs Island, Aspland Island, and O'Brien Island to the 

 south, is usually regarded as a part of the South 

 Shetlands archipelago (see map. Fig. 10). But 

 there is a good case for its separation as an 

 independent group, and for regarding it as on a 

 parity with the South Shetlands and the South 

 Orkneys. There is a wide sea gap between Gibbs 

 Island and King George Island (South Shetlands), 

 much wider than the distances between the in- 

 dividual islands of either group; moreover, the 

 Elephant and Clarence Group is geologically quite 

 different from the South Shetlands with their 

 thick coverings of andesite lavas, which are absent 

 from all the visited islands of the Elephant and 



Clarence Group. 



, . , , r 1 T-1 I ,. J Fig. 10. Elephant and Clarence Group. 



Landmgs on the islands of the Elephant and & f 



Clarence Group have been few, and consequently the geological data up to date are very scanty. In 

 the following pages the available information is assembled and supplemented by the investigation of 

 new material from Clarence Island and Gibbs Island, collected during expeditions ot the ' Discovery II '. 



C SiO'N 



;e5 



SCALE OF MAU 



SI 30 



55 



S"! w 



ELEPHANT ISLAND 



During the Salvesen expedition of 191 3 the late Mr David Ferguson passed close to Elephant 

 Island, but was unable to land owing to stormy conditions. He made a few observations from the 

 ship, however, and has recorded them as follows i^ 'The rocks at the south-east corner of the island 

 [Cape Lookout?] are light grey to dark, and more or less banded. The grey rocks appear to be stratified 



1 G. W. Tyrrell, 'A Contribution to the Petrography of the South Shetland Islands, the Palmer Archipelago, and the 

 Danco Land Coast, Graham Land, Antarctica', Trans. Roy. Soc. Edin. liii, pt. i, 192 1, p. 78. 



2 D. Ferguson, 'Geological Observations in the South Shetlands, the Palmer Archipelago, and Graham Land, Antarctica', 

 Trans. Roy. Soc. Edin. Liii, pt. i, 1921, p. 35. 



