96 STEPHEN TABER 



Passing westward from Jamaica, soundings show that the steep 

 southern escarpment of the Bartlett Trough continues toward 

 Swan Island, and everywhere with abrupt changes in slope at top 

 and bottom. Swan Island has the topographic characteristics of 

 a horst which has remained standing within the zone of subsidence 

 (see Fig. i). 



Great Swan Island is only 2.5 km. in length and about 20 m. 

 in height; Little Swan Island is scarcely more than a reef. The 

 submarine slopes in the vicinity of the islands are precipitous: 

 on the south a sounding of 1,053 fathoms (1,926 m.) was obtained 



Fig. I. — Profiles of the Bartlett and Anegada Troughs. Vertical and horizontal 

 scales the same. Additional soundings would show the scarps to have steeper rather 

 than gentler slopes. 



within 10 km., the descent continuing until a depth of 2,136 m. 

 is reached 16 km. from the island, after which the sea-bottom 

 rises rapidly to the edge of the submerged Honduras-Jamaica 

 Plateau; toward the north, a depth of 3,010 fathoms (5,505 m.) 

 is attained within 32 km. of the island, thus giving an average 

 slope of about one in six. 



The latter sounding was obtained in a long, narrow depression 

 lying at the foot of the scarp. The 3,000-fathom contour surround- 

 ing the depression (see map, Plate I) extends eastward from Swan 

 Island along the base of the scarp for 200 km. or more. It has an 

 average depth, below the floor of the Bartlett Trough in this 

 vicinity, of over 1,000 m., the deepest sounding recorded being 



