44 PROCEEDINGS OF THE WASHINGTON MEETING 



must have developed during subsequent submergence. The flat, therefore, 

 can not be due to the growth of tbe reef. 



The members of the Saint Martin group have indented shorelines, sea-cliffs, 

 and an unusually fine development of bay-bars. The relations on the wind- 

 ward side of the Saint Martin Plateau are similar to those north of Saint 

 Thomas. The outer, deeper flat, from 26 to 36 fathoms in depth, has a maxi- 

 mum length, east and west, of over 30 miles. It seems composed of two ter- 

 races. The scarp on its landward side is distinct and in places is about 50 

 feet high, between 20 and 28 fathoms, as off the east end of Scrub Island, 

 east of Anguilla Island, 



As some of the submerged valleys on the east side of the Saint Martin 

 Plateau resemble valleys in the Upper Cretaceous Anacacho limestone Texas, 

 it appears that not only must the scarp line which has been pointed out be 

 interpreted as a former shoreline, but that these channels with steep heads 

 must be interpreted as former drainage lines which were subaerially cut and 

 afterward submerged. The Anacacho limestone in the Brackett quadrangle 

 is similar in general character to the limestone which composes Anguilla and 

 Tintamarre. 



While the shoreline stood some 20 fathoms lower than now, the Saint Martin 

 Plateau must have been entirely above sealevel. The biologic evidence is in 

 accord with this interpretation, but at present it alone is not sufficient to be 

 decisive. 



Antigua is another island with an indented shoreline. It shows typical 

 instances of submerged valleys and fairly good examples of pouch-shaped har- 

 bors. Profiles off the southeast shore exhibit essentially the same features as 

 the profiles on the Virgin Bank and tbe Saint Martin Plateau. If sealevel 

 stood 20 fathoms below its present stand, Antigua and Barbuda would be 

 united. Doctor 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 Saint Martin 

 Plateau, and on the Antigua-Barbuda Bank, it seems to me, may be accounted 

 demonstrated. 



A set of profiles on the same vertical scale — (a) across Havana Harbor, 

 showing depth of filled channel; (6) off the north side of Saint Thomas; (c) 

 off the west side of Anguilla; (d) off the southeast coast of Antigua; (e) 

 Mosquito Bank, off Nicaragua — all indicate a rise of sealevel by an amount 

 of about 20 fathoms. There is in the Virgin Islands and in Cuba clear evi- 

 dence of a lowering of sealevel by about 20 fathoms, perhaps more, previous 

 to resubmergence. Although the evidence for the other areas is not definite 

 as to the return of sealevel to a former stand, the similarity of the profiles 

 suggests that it also occurred in them. As this lowering and subsequent rise 

 of sealevel affects a large area, it appears too wide-spread to be explained by 

 local crustal movement. The changes in position of strand-line here noted are 

 more reasonably explained by the lowering of sealevel, due to the withdrawal 

 of water in the Pleistocene ice epochs to form to great continental glaciers, 

 and the raising of sealevel after each epoch through the melting of the glaciers ; 

 but the volume of evidence supplied by this area is perhaps not large enough 



