328 THE VOYAGE OF THE 'DISCOVERY' [Appx, 



basalt, and it is found also at a height of 1,500 feet on the side of 

 Mount Erebus. 



Winter Quarters. 



About four square miles of bare rock, entirely of volcanic origin, 

 was the only land within walking distance of the 'Discovery's' 

 Winter Quarters, and therefore did not offer a promising field 

 for discovering the geological history of South Victoria Land. Of 

 this area, Castle Rock, a crag 400 feet above the snow and 1,400 

 feet above sea level, consists of palagonite-tuff very similar to that 

 at Cape Adare and Possession Island, and is probably the neck of 

 some ancient volcano. 



The three heights called Harbour Heights, as well as the cone 

 called Crater Hill, are scoria cones, but the chief ejecta from 

 them consists of black fine-grained basalt, both compact and 

 vesicular. On one of these masses of black basalt, near the base 

 of Castle Rock, a small quantity of native sulphur was found, and 

 this was the only example of solfataric action observed in the 

 immediate neighbourhood 



At the base of Crater Hill, on the S.E. side, an olivine basalt 

 of high specific gravity was found ; a similar basalt also appears 

 on Cape Armitage and the rock at both places occurs in almost 

 horizontal sheets. 



Observation Hill, about 750 feet high, consists principally of 

 hornblende-trachytes, and these, having been erupted from a local 

 centre, practically form the hill. The rock with parallel stmcture 

 which is found at the north foot of the hill and in the Gap is an 

 earlier extrusion than the rest, and lies unconformably below them. 



Turning now to the other islands, White Island is so covered 

 by detritus that it is only near the summit that the rock met with 

 is undoubtedly in situ. Here also extrusions of basalt are found, 

 which suggest that this island is of the same general age as Ross 

 Island. 



Black Island likewise consists mainly of basalt, and near the 

 north-west extremity vesicular and amygdaloidal flows were 

 encountered. At the south-west end yellow trachytic rocks form 

 a bold headland, but do not cover an area greater than about four 

 square miles. 



Brown Island has a well-defined crater at its summit, which 

 is quite undenuded, and from it have issued basalts in various 

 conditions. A great part of the summit consists of a yellow 



