62 vaughan: virgin and leeward islands 



shore-line but these channels, with steep heads must be inter- 

 preted as former drainage lines which were subaerially cut and 

 afterwards submerged. The Anacacho limestone in the Brackett 

 quadrangle (of the U. S. Geological Survey) is similar in general 

 character to the limestone which composes Anguilla and Tinta- 

 marre. 



While the shore-line stood some 20 fathoms lower than now, 

 most of the St. Martin plateau must have been above sea- 

 level. The biologic evidence is in accord with this interpre- 

 tation, but at present it alone is not sufficient to be decisive. 



Antigua is another island with an indented shore-line. It 

 shows typical instances of submerged valleys, and fairly good 

 examples of pouch-shaped harbors. Profiles off the southeast 

 shore are shown in figure 4. These exhibit essentially the same 

 features as the profiles on the Virgin Bank and the St. Martin 

 plateau. If sea-level stood 20 fathoms below its present stand, 

 Antigua and Barbuda would be united. Dr. Bartsch has 

 especially studied the land Mollusca and says: "The land shells 

 show that these islands must have been connected in very recent 

 time." 



The deduction that there has been in Recent geologic time 

 submergence to an amount of about 20 fathoms in the Virgin 

 Islands, on the St. Martin plateau, and on the Antigua-Bar- 

 buda bank, it seems to me, may be accounted demonstrated. 



The upper part of figure 4 shows a set of profiles, all on the 

 same vertical scale. They represent profiles (a) across Havana 

 Harbor, showing depth of filled channel; (b) off the north side 

 of St. Thomas ; (c) off the west side of Anguilla ; (d) off the south- 

 east coast of Antigua; (e) Mosquito Bank, off Nicaragua. All 

 these profiles indicate a rise of sea-level by an amount of about 

 20 fathoms. There is in the Virgin Islands and in Cuba clear 

 evidence of a lowering of sea-level by about 20 fathoms, perhaps 

 more, previous to resubmergence. Although the evidence for 

 the other areas is not definite as to the return of sea-level to a 

 former stand, the similarity of the profiles suggests that it also 

 occurred in them. What caused this lowering and subsequent 

 rise of sea-level? As it affects a large area, it appears too wide- 



