SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 69 



already shown (Text-fig. izd), illustrates clearly the gradual descent of the continental slope from the 

 Falkland Islands to a depth of slightly over 3000 m., the comparatively sharp rise to the hank itself 

 and the fairly steep slope away to an irregular bottom at an average depth of 4500 m. (2461 fm.). 

 South of the bank the contours as now drawn show that the slope is steeper than was supposed, though 

 the average gradient as determined from five crossings is not more than 3!°. Several good continuous 

 records were obtained here with the ' Acadia ' recorder and from these it can clearly be seen that one 

 of the most prominent features is the considerable irregularity of the bottom down the slope. This is, 

 perhaps, most clearly seen at depths of less than 3000 m. (1641 fm.). As we have already mentioned, 

 such irregularity of the bottom, just south of the connecting link, appears to be a well-marked feature 

 of this sector of the Arc. 



Eastwards towards the Shag Rocks the recent soundings are in close agreement with those deter- 

 mined prior to 1932, and provide confirmation of the suggested line of the connexion. Nine more 

 soundings of less than 1000 m. were obtained between 51° W and 53° W on the line from the Burdwood 

 Bank towards South Georgia with a minimum depth of 581 m. (318 fm.). Farther to the east a series 

 of soundings between South Georgia and the Falkland Islands provides valuable evidence of the 

 extensions westward of depths of less than 2000 m. (1094 fm.), to a position in approximately 53° S, 

 46" 40' W, and a formerly isolated sounding of less than 2000 m. is now linked up with the Shag Rocks, 

 some 170 miles to the east. 



The soundings obtained on this east and west line have been corroborated by five lines of soundings 

 in a north and south direction, between the meridians of 43° W and 46° W. Agreement with the 

 previous results was again very good. As will be seen from PI. XXIII two of the lines in this series 

 were run in weather which allowed soundings to be taken at intervals of 30 min. (except for one gap) 

 or approximately every 4I miles, and there can be little possibility that any outstanding feature ot the 

 bottom was missed in this region. 



Immediately south of the Arc, between 44° W and 45° W, and in the latitude of approximately 

 54° 30' S, there is an interesting deep fold, some 50 miles in length as at present known, where two 

 depths of more than 5000 m. were obtained. The western end was determined by the ' Meteor' m 1926 

 and was shown on our original chart as an isolated deep sounding. In November 1932 a line of 

 soundings on a southerly course crossed this fold about 25 miles to the east of the position of the 

 'Meteor' sounding. No sounding of more than 5000 m. was obtained, but four depths, rangmg 

 between 4879 m. (2668 fm.) and 4998 m. (2733 fm.) were determined over a distance of 7 miles between 

 the latitudes of 54° 30' S and 54° 37' S, in the longitude of 44'^ 36' W. This narrow trench is followed 

 by a sharp rise to a sounding of 2776 m. (1518 fm.) in a distance of 4I miles; equivalent, roughly, to 

 a slope of 1 5°. This is considerably steeper than the slopes normally found far from land. It is based on 

 only two soundings, and thus, although the angle cannot be less than 15°, the recorder m^ght well 

 show parts of it to be steeper, especially if the ship moved at right angles to the contours. This further 

 proof of parallel folding adjacent to the main ridge must be regarded as strong support for the theory 

 of the arcuate connexion. 



In April 1934 the 'Discovery II' obtained a single sounding of 5088 m. (2782 fm.) at St. 1335 

 (54° 37-8' S, 44'' 12-6' W) to the east of the previous line. Later, unfavourable weather prevented us 

 from obtaining soundings on a line which crossed the fold from south to north, in approximately 

 45° 30' W, at a point where the soundings of the 'Meteor' suggest an extension of the fold to 



the west. 



In the immediate vicinity of the Shag Rocks the recent soundings show that the 500 m. (273 tm.) 

 contour to the west of the Rocks should extend some 25 miles farther to the west ; and the hmit of the 

 1000 m. (547 fm.) contour in the same direction can now be determined with fair accuracy. 



