8o DISCOVERY REPORTS 



a survey of not less than 500 miles of the bottom. Owing to the thick weather prevalent this season 

 not all these runs could be used for the survey charts, but although they were not accurate enough for 

 a hydrographic survey certain sounding runs, made on dead reckoning, have been of considerable aid 

 in the construction of our present bathymetric chart of this area. The ship's tracks during the periods 

 of continuous soundings in 1934-5 ^^'^^ 1936-7 will be found in Text-fig. 4, p. 47. 



With the exception of Nelson Strait, which is comparatively wide throughout its length, the straits 

 between the islands of the South Shetlands Group are usually narrower at their northern ends. 

 Moderately deep water is found in all the southern entrances, and throughout the straits, but the 

 northern entrances are all shallow. In some instances they are unnavigable even by small ships. 

 Rocks and reefs abound here, and there are strong currents. 



In the straits themselves and around the southern coasts of the various islands there is little or no 

 coastal shelf of shallow water, and the slopes up to the land are considerable. In McFarlane Strait, 

 which lies between Livingston and Greenwich Islands, there are depths of more than 500 m. (273 fm.) 

 in the southern entrance, and the 250 m. (137 fm.) contour extends for some 7 or 8 miles towards the 

 northern entrance. Depths of more than 100 fm. (182 m.) were recorded for a further 3 miles in a 

 northerly direction and only in one place, off Yankee Harbour in Greenwich Island, is there any 

 resemblance to a coastal shelf. Here, a shallow shelf, with depths of less than 40 fm. (73 m.), stretches 

 out for about a mile from the harbour entrance, but the slope away from this to the deeper water is 

 considerable. The angle of descent averages from 15 to 18", with a maximum slope of 26^ Yankee 

 Harbour itself is of interest as, apparently, there is a bar at the entrance, with considerably deeper 

 water in the anchorage. 



The southern part of English Strait, which separates Greenwich Island from Roberts Island, is not 

 more than i| miles wide, but the width increases towards the centre of the strait before narrowing 

 again for the northern entrance. A narrow trough, more than 250 m. (137 fm.) in depth, runs up the 

 strait almost to the numerous small islands which infest the northern entrance. The coasts of both 

 Greenwich and Roberts Islands fall away sharply into this trough for some miles, but with the widening 

 of the strait into Discovery Bay the deeper water continues north close to Roberts Island. The 

 average slope of the eastern side of this trough appears to be about 14°. 



The topography of the bottom of Nelson Strait, which lies between Roberts and Nelson Islands, 

 differs considerably from that of the others. The strait is wide throughout, with a minimum width of 

 6i miles, and the coastal shelf on the eastern side of Roberts Island extends for some 3 or 4 miles. 

 The northern entrance, unlike those of the other straits, appears to be remarkably free from dangers, 

 although there are strong currents and some tide-rips. Depths of more than 250 m. (137 fm.) are 

 found on the eastern side of the strait, and this moderately deep trough then curves to the north-west 

 towards the coast of Roberts Island. The western coast of Nelson Island is steep-to, and in a position 

 a few miles south of Harmony Cove there is a small but moderately deep hole with a maximum depth, 

 so far determined, of 324 fm. (593 m.). The slope into this hole from the south-east is approximately 



23r- 



With the approaches to Fildes Strait, between Nelson and King George Island, there is a marked 

 change in the character of the bottom topography. South of Nelson Island there is a moderately wide 

 coastal shelf and, although it is penetrated by depths of more than 250 m. (137 fm.) in the approaches 

 to Fildes Strait and in Admiralty and King George Bays, this shelf continues along the whole south 

 coast of King George Island. In the approaches to Fildes Strait, which in itself is only navigable by 

 boats, and that with difficulty, depths of more than 250 m. (137 fm.) extend over a wide area, and are 

 found moderately close to both shores. The slopes here are slight. 



Admiralty Bay, in King George Island, reverts more to the character of the straits at the western 



