CONDITIONS OF SEDIMENTARY DEPOSITION. 497 



the Eastern Caribbean deep the declivities are such as would 

 thus be determined ; the northern and southern slopes between 

 which the current flows are approximately equal and steep; the 

 slope of the eastern side is also steep and lies at right angles to 

 the course of the current in the position of a bank forming in 

 the lee of a terrace, and the rise from the abyss westward in the 

 direction of the current is relatively gradual. 1 



This basin is the one most advantageously situated to exhibit 

 slopes of deposition. Bartlett's deep lies like a narrow canon 

 across the course of the current, and the small triangular basin 

 immediately east of Yucatan, while it shows a steep slope north- 

 ward in the direction of the current, presents similar declivities 

 along its other two sides which are possibly scoured by the 

 waters converging to pass out at the apex, the Yucatan channel. 

 The steepest slope of the Gulf of Mexico from the 100th to the 

 2000th fathom line, is in the position of a lee -bank northwest 

 of the Yucatan plateau, and the contours elsewhere are appar- 

 ently modified by the scouring action of the current as it sweeps 

 around the basin, and by terrigenous deposits from the adjacent 

 shores and rivers. The Blake plateau, over which the Gulf 

 stream sweeps north of the Bahamas, is clean, hard limestone, 

 but a lee -bank of mud and ooze is forming on its short, steep 

 slope into deep water. Agassiz says (p. 277): "There we pass 

 from the comparatively coarse shore mud to finer and finer ooze, 

 which becomes an impalpable silt in the deeper water beyond 

 one or two thousand fathoms, assuming at the same time a 

 lighter color." 



Another illustration may be found in the deposits of silt 

 which form the edge of the continental plateau off the North 

 Atlantic coast of America. Agassiz has mapped the width of 

 the plateau as covered with " silicious shore deposits," and 

 examination of some of the samples of bottom in the Coast 

 Survey office, for which opportunity has been most courteously 

 extended to the writer, shows that the surface of the plateau is 



1 See bathymelric map opp. p. 98, "/Three Cruises of the Blake." 



