SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 83 



Buckle Island appears to lie athwart the ridge. At the south-western corner of the island the slope 

 to moderate depths is greater than off Young Island, ly"" being the approximate angle, and corre- 

 sponding to this we find that north of Cape Davis, on the eastern side, the slopes are approximately 

 I2|°. North and east of the island the descent to deeper water appears to be moderate. 



No soundings were obtained on a direct line between Borradaile and Buckle Islands, but from the 

 evidence of the line of soundings a few miles to the east it may be suggested that the ridge is continuous 

 between these islands at depths of less than 500 m. (273 fm.). From the soundings obtained south-east 

 of Buckle Island it appears probable that there is also a similar connexion with Sturge Island. 



TRISTAN DA CUNHA GROUP 

 (Tristan da Cunha 37° 06' S, 12° 18' W) 



In November 1933 the 'Discovery II' approached Tristan da Cunha from the north. Continuous 

 soundings were taken with the 'Acadia' recorder from 36° 07' S, 12° 31-5' W to the anchorage, 

 a distance of 57 miles. At the beginning of the run the bottom was comparatively level at depths varying 

 between 2000 and 2100 fm. (3658 and 3840 m.), and this condition persisted to within a distance of 

 approximately 12 miles from the island. From this point soundings shoaled continuously, though at 

 times with considerable irregularity in the bottom, to a depth of approximately 1650 fm. (3017 m.). 

 The slope now became much steeper, and from a depth of 1079 fm. (1973 m.) the 100 fm. (183 m.) line 

 was reached in a distance of 2-9 miles; equivalent to an average slope of i8^°. A maximum slope of 

 25° was recorded over a distance of 0-4 miles, between the depths, approximately of 350 and 165 fm. 

 (658 and 302 m.). We have already referred to this slope (p. 54), which was one of the longest over 

 which we were able to obtain continuous soundings, and the profile of the last 33 miles of the approach 

 is shown in Text-fig. 9, p. 55. 



On leaving the anchorage our course lay north-west, then west-by-south and, after reaching deep 

 water, approximately south (see Text-fig. 3^, p. 46). Continuous soundings were again taken and the 

 run continued to Nightingale Island and thence to Inaccessible Island, a total distance from Tristan 

 da Cunha of 45 miles. West of Tristan da Cunha the ' Discovery II ' passed just over i mile off-shore 

 and the minimum sounding obtained was 130 fm. (238 m.). Shortly afterwards the depth increased 

 rapidly from 171 fm. (313 m.) to 1044 fm. (1909 m.) and for the next 4 miles the bottom remained very 

 irregular at depths varying between 956 and 11 16 fm. (1748 and 2041 m.); there was then a gradual 

 rise towards Nightingale Island, where there is moderately deep water close off-shore. Between 

 Nightingale and Inaccessible Islands the bottom was again very irregular, with a maximum depth of 

 597 fm. (1092 m.) about mid-way between the two islands. The slope of the bottom in either direction 

 from here was moderately steep. 



At Inaccessible Island depths of 100 fm. (183 m.) were obtained at a distance of 2-2-5 "^i^^s from 

 the land, both on the run across from Nightingale Island and on the line of departure to the south-west. 



Tristan da Cunha, Nightingale and Inaccessible Islands are all steep-to, the two former to a greater 

 degree. At Tristan da Cunha, on the approach from the north, depths of 100 fm. (183 m.) were 

 reached at a distance of 1 7 miles from the land and on the departure to the north-west the edge of 

 this narrow coastal shelf lay at a distance of 1-3 miles off-shore. To the west of the Island, as we have 

 already stated, soundings were over 100 fm. at a distance of 1-15 miles from the land. Littlehales 

 (1932, p. 21) has stated that submarine slopes of 33^° have been found at Tristan da Cunha; we did 

 not record any slope of this magnitude but, in view of the evidence of our soundings about the nature 

 of the bottom to the north and west of the island, such slopes may well exist. 



