SOUTH SHETLAND ISLANDS AND ADJACENT WATERS 231 



specimens there after the loss of the ' Endurance ', has decided that the rocks, which were 

 critically examined by Tyrrell, are metamorphic and probably altered volcanic ashes, but 

 too metamorphosed to be properly identified. It would thus appear that although 

 the soundings indicate the presence of a ridge, the structure of these islands themselves 

 cannot be used as evidence of a former land connexion. 



Hydrological observations tend to show that the oceanic warm deep-water layer in 

 Drake Passage, in which the maximum temperature is found at about 500-600 m., occurs 

 in the Bransfield Strait with the maximum temperature at an average depth of 300 m. 

 This difference of levels inside and outside the strait is accounted for by the rise of the 

 ocean bed towards the South Shetlands which forces the south-flowing warm deep water 

 upwards to a level where it can enter the strait. It is almost certain that it enters between 

 Smith and Snow Islands, where the soundings show a channel with an average depth of 

 600-700 m. It then passes across the smaller basin in a south-easterly direction and 

 enters the larger basin to the south of Deception Island. On the evidence of the present 

 soundings there appears to be a ridge between Deception and Tower Islands, but the 

 position of the 500 m. contour is a little uncertain, as it could also be drawn to run east 

 and west showing a channel with a depth of 600 m. and over. Such a channel would 

 allow the passage of the warm deep water. The characteristics of this layer gradually 

 grow weaker towards the eastern end of the main basin, disappearing altogether south 

 of Elephant Island. Hydrological observations in this area show that the chief water 

 movement is an inflow of Antarctic surface water from the Weddell Sea. 



In the vicinity of Joinville Island and to the north-east of it, the only soundings 

 available are those taken by the 'Pourquoi Pas?' in 1908-10 and the 'Antarctic' in 

 1901-3. These, however, in conjunction with our zigzag Hne of echo soundings south 

 of Clarence Island show that Trinity Peninsula is continued as a shallow submarine 

 plateau towards the north-east and eventually joins up with the main Orkneys— Shet- 

 lands ridge. Here large icebergs from the Weddell Sea are frequently found stranded. It 

 is hoped to obtain more soundings south of Clarence Island to clear up some doubtful 

 points, one of which is the possible existence of a channel running east and west and 

 shown at the moment only by a very few soundings. The hydrological evidence here is 

 more against than for the existence of such a channel. 



While the 'Discovery H' was on passage from Port Lockroy, Wiencke Island, to 

 Deception Island by way of the De Gerlache Strait, continuous echo soundings were 

 taken which showed that up the centre of the strait there was a channel with an average 

 depth of between 600 and 700 m. Near Cape Murray, at the eastern end of the Strait, 

 the soundings exceeded 1000 m. for several miles. Nine soundings of over 1000 m. were 

 obtained, the maximum being 1141 m. On coming out of the strait we continued up 

 towards Trinity Island, intending to pass through Orleans Channel, but owing to the 

 presence of pack ice we were compelled to turn north before entering it. On this north- 

 ward passage we discovered the existence of a reef to the west of Farewell Rock, Trinity 

 Island. We passed between this reef and the island, the soundings shoaling gradually 

 to 66 m. and falling away again quite sharply on the northern side. 



4-2 



