372 CARNEGIE INSTITUTION OF WASHINGTON. 



show was developed when the sea-level was about 20 fathoms, or 

 slightly more, lower than now. The escarpment extending from the 

 islands north of Culebra Island, east of Porto Rico, and along the north 

 side of 8t. Thomas, and the escarpment on the seaward face of the out- 

 lying shoals, apparentl}^ can be explained in no other way. 



The indentations on the outer margin of the outer flat may have been 

 caused by elevation and stream-cutting after its formation, or they 

 may be due to initial marginal irregularities which have not been 

 obliterated. 



The approximate accordance in level of the tops of the outlying 

 shoals at depths between 17 and 20 fathoms has been mentioned. 

 These summits accord in height with a flat or gently sloping zone lying 

 above and nearer shore than the deeper flat. It is scarcely represented 

 on the seaward side of the promontories, viz. Cockroach and Cricket 

 rocks, and Outer Brass and Little Hans Lollik islands. However, it 

 spreads out on the flanks of the promontories and ranges from 0.5 mile 

 to nearly 1.5 miles in width; it is separated on its seaward side by a 

 steep slope or escarpment from the deeper fiat and on its landward side 

 by an escarpment about 36 feet in height from a terrace which has a 

 depth of 7 to 10 fathoms. The descent is sudden from the shore to 

 about 6 fathoms, which is near the inner margin of the highest sub- 

 marine terrace. This terrace, also, is narrow on the tips of the promon- 

 tories mentioned, but widens on their flanks and below the shores of the 

 main island. 



The submerged valley in Charlotte Amalia Harbor has a depth of 

 10 fathoms. 



The interpretation of the history of the higher flats is beset with 

 difficulties. Theu* narrowness or absence on the promontory tips sug- 

 gests that they may be older than the deeper flat and were cut away dur- 

 ing its formation, and that subsequent to the formation of the latter, 

 after perhaps a brief interval of still lower stand of sea-level, the entire 

 area has been resubmerged, perhaps to an amount somewhat exceeding 

 the initial submergence. 



The relations on the windward side of the St. Martin Plateau are 

 similar to those north of St. Thomas, except that the boundaries of the 

 upper terraces do not seem so definite. This may be due to fewer 

 soundings and the smaller scale of the map. The outer, deeper flat, 

 from 26 to 36 fathoms in depth, has a length east and west of over 30 

 miles. 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. The contouring of the bottom around 

 Antigua Island has not been completed, but enough has been done to 

 show that it also is terraced. 



As the interpretation of the data accumulated is still incomplete, 

 deductions here presented are only preliminary. The subject is 



