74 BULLETIN OF THE 



tendent of the Coast Survey, in running a number of lines normal to the 

 coast, south of Cape Hatteras and north of the Bahamas, and extending 

 them into deep water. Commander Bartlett has sent his Report to 

 Professor Hilgard, the Superintendent of the Coast Survey, who has 

 kindly allowed me to make use of these results in connection with my 

 present work on a general report of the dredging expeditious of tlie 

 " Blake." The accompanying map has kindly been prepared ibr my use 

 by the Superintendent of the Coast Survey.* 



As was to a certain extent anticipated, the lines show the existence 

 of an extensive plateau, of a triangular shape, reaching from tlie Bahamas 

 to immediately south of Cape Hatteras, where this plateau gradually 

 passes into the continental plateau, extending northward, which is lim- 

 ited by the 100 fathom line, and has a steep slope extending to deep 

 water. 



The eastern edge of this plateau is from 300 to 350 miles from the 

 coast, and forms a gigantic submarine plateau, with an abrupt slope 

 passing into deep water. For the sake of brevity I shall call this 

 plateau the " Blake plateau." The eastern edge of the slope of the 

 Blake plateau commences at an average depth of at least 400 fath- 

 oms, so that the general profile of the lines extending normally across 

 the Blake plateau show a gradual incline from the shore to a depth 

 of about 50 fathoms, then a somewhat abrupt slope to a depth of about 

 iO^ fathoms, then a very gradual descent to the edge of tlie sharp, steep 

 slope forming the outer eastern edge of the Blake plateau, at a depth 

 of nearly GOO fathoms. 



It is interesting to speculate how this peculiar profile, so different 

 from that of any other part of our coast, was formed. The explanation 

 to my mind is comparatively simple. The present outer eastern edge 

 of the Blake plateau, which is now at a depth of GOO fathoms, was 

 at one time at a much higher level. In fact, I assume that tliis slope 



* These lin'es have, cluri;is the season of 1882-83, been extended south of the 

 Bahamas as far as Porto Kico. Under the direction of Professor Hilgard, the 

 "Blake," in command of Lieutenant-Commander Browson, U. S. N., ran normals 

 into deep water, showing that the great submarine Bahama plateau developed by 

 Commander Bartlett commences slightly to the westward of Great Abaco, and 

 extends thence northward, as is shown on the accompanying map. Lieutenant- 

 Commander Browson showed further that to the south the eastern edge of the 

 Bahama Bank extended but a short distance seaward parallel to the general line 

 of the outer row of islands of the group, till it united with the great plateau upon 

 which Porto Rico and the Caribbean Islands crop out, leaving probably one or two 

 deep passages extending towards the old Bahama Channel north of San Domingo 

 and Cuba, leading to the Windward Passage. 



