304 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 14 
end of Porto Rico in compliance with a request made by the Navy 
Department for special geologic information on the territory examined. 
The field work was done between May 21 and June 24, 1919. The col- 
lections made were examined by the following of my official colleagues: 
Mr. C. P. Ross examined the igneous rocks; Dr. T. W. Stanton 
identified the Cretaceous mollusks; Dr. J. A. Cushman identified the 
Tertiary Foraminifera; Dr. R. 8. Bassler, the Bryozoa; and Dr. C. W. 
Cooke, the Tertiary Mollusca. The corals were identified by me. 
LOCATION AND GENERAL FEATURES 
The Virgin Islands, except Saint Croix and its outlying islets, rise 
above a shallow bank that extends northeastward from Porto Rico to 
Anegada Passage. The number of the islands is about 100. They are 
separated from one another and from eastern Porto Rico by water 
having a maximum depth of 16 to 18 fathoms. Except Anegada 
which rises only about 30 feet above sea level, the larger islands attain 
altitudes ranging from about 650 feet (Culebra) to 1800 feet (Tortola) 
in altitude. The highest point in Saint John is 1,277 feet; in Saint 
Thomas, 1,550 feet; in Culebra, 650 feet; in Vieques, 981 feet. The 
islands are well dissected and as a rule have gradual slopes, except 
along the shores where there may be high sea-cliffs. The absence of 
inland bluffs is one of the striking features of the topography of these 
islands. The shore line is indented by bays, which indicate geologi- 
cally Recent submergence. 
The Virgin Bank is about 90 sea miles long and from 24 to 30 sea 
miles wide. The depth of water on it is as much as about 40 fathoms 
around its edges where there are steep descents to deep water, to over 
3,000 fathoms between Saint Thomas and Saint Croix, to about 1,200 
fathoms in Anegada Passage, and to 400 fathoms on the north side, 
where there is an apparently gradual slope to depths of about 3,600 
fathoms at a distance of about 55 sea miles north of the bank. Along 
a line about 25 sea miles long through the Virgin Passage the depth 
ranges from 12 fathoms in the shallowest part to about 40 fathoms on 
the northern edge—the range in relief on the flat being only about 
132 feet in about 25 miles. The surface of the bank exhibits sub- 
marine terraces both off the shores of Saint John and Saint Thomas 
and in the Virgin Passage. The living coral reefs have grown up on 
the terraced surface of the bank after an episode of submergence, a 
relation which I have described in several papers. 
Between the Virgin Bank and Saint Croix there is a deep of 3,400 
fathoms which is continuous eastward into Anegada Passage, whose 
