52 



DISCOVERY REPORTS 



tuff made up of angular fragments of the fluxional rock, a biotite-rhyolite, and orthoclase-porphyry 

 or felsite with only sparse phenocrystic quartz. Finally, a fragment collected from the scree on the 

 cliffs of a rocky islet near the anchorage turns out to be a crushed sericitic quartzite of a distinctly 

 ancient aspect. 



DECEPTION ISLAND 



Deception Island is the best known of the South Shetland Islands. Dr Thomas ((2), p. 81) has 



commented on the earlier literature of the island. Mr Ferguson added a few details and published 



two excellent photographs {op. cit. p. 44; pi. iii, figs. 2, 3); but the fullest recent description is that 



by Holtedahl ((3), pp. 29-47). Deception Island apparently represents a huge breached crater flooded 



S£. WALL OF OecePTiON HflKBWR , SOUTH SHeTLAMOS. >«i- ^.S^'i OMctc^y . STATION 1484 







ttju-46wu^ 





^//^<^'>>' 



Souk 



.(Sjj SeoLclv 





dan* 





I II 



--^*"^4, 



''^'':c'' 







N ■ A .M. 



Fig. 7- 

 by the sea, of which the inner diameter is about 8 km. Holtedahl believes, however, that it is not a 

 single large crater, but a volcanic ring mountain built around a caldera subsidence bounded by 

 a circular fault or series of faults. 



Dr Mackintosh collected material from the cliffs and slopes on the south-east side of the whaler's 

 anchorage near the entrance to Deception Harbour. These form a narrow ridge of land separating the 

 anchorage from Bransfield Strait (see Dr Mackintosh's sketches. Fig. 7). He reports that the whole 

 of the cliffs shown in the sketch, except beyond Neptune's Bellows,^ consist of an 'agglomerate of 

 ashes in a yellowish matrix'. It is possible that the yellow colour is mainly superficial, as freshly 

 broken surfaces generally seem darker. The slopes below the cliffs are mainly of a soft gravel obviously 

 formed from the disintegrated agglomerate, carrying a fair proportion of solid boulders of agglomerate, 

 and here and there boulders of a harder dark rock presumably derived from intrusions in the agglo- 

 merate (andesitic basalt). 



1 Apparently the name given to the entrance channel of Deception Harbour. 



