316 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 14 
that of other agents was of minor importance. If the work of these 
organisms in forming deposits concealed under water can be evaluated 
by their work in deposits exposed to view, the conclusion would be 
drawn that they played only a minor réle in the formation of the 
Virgin Bank. There is as yet no evidence showing intense deformation 
during later Oligocene time in the Virgin Islands and Porto Rico such 
as is known to have taken place in the Dominican Republic. 
(6) Subsequent to early Miocene time there has been uplift, greater 
along the axis of Porto Rico and the Virgin Bank than on the flanks, 
bringing Miocene and older Tertiary sediments, in places where they 
are present, above sea level. The Tertiary sediments are tilted and 
gently flexed but they have not been so much deformed as the Upper 
Cretaceous deposits. It is about this time that the land connections 
permitting migration of land animals from Anguilla to Porto Rico, 
Haiti, and Cuba seem to have existed. Saint Croix seems to have been 
connected with Anguilla, Saint Martin, and Saint Bartholomew. 
(7) The period of high stand of land was followed by faulting, such 
as I have several times described recently; but, as pointed out by 
Woodring, the faulting was concomitant with folding. By these 
processess Anegada Passage between the Virgin Bank and Anguilla 
was produced and the islands assumed very nearly the outlines and 
arrangements of today. 
(8) Subsequent to the episode of faulting there was emergence of 
the land, and terracing of the margins of the Virgin Bank, followed by 
submergence. In places in Porto Rico and along the Cordilleras reet, 
which extends eastward from the northeast corner of Porto Rico, there 
has been local emergence due to differential crustal movement. 
(9) The living coral reefs on the Virgin Banks are growing on an 
extensive flat in a period of geologically Recent submergence. ‘This 
flat is geologically an old feature. Its origin in large part at least 
may reasonably be attributed to the long period of erosion following 
early Tertiary mountain-making. 
List or PUBLICATIONS ON THE GEOLOGY OF THE VIRGIN ISLANDS 
Curve, P. T., On the geology of the northeastern West India Islands: Vetensk. Akad. 
Handl. 9: No. 12,48. 1871,2 maps. 
Cooker, C. Wytxe, Orthaulaz, a Tertiary guide fossil: U. 8. Geol. Survey Prof. Paper 
129: 23-37, pls. 2-5. 1921. 
Lozeck, A. K., The physiography of Porto Rico: New York Acad. Sci. Scientific Survey 
of Porto Rico and the Virgin Islands, 1‘: 301-379. 1922. 1 map. This 
work contains information on Vieques and Culebra. 
Qury, Joun T., The building of an island, being a sketch of the geological structure of 
the Danish West Indian Island of Saint Croix, or Santa Cruz, pp. 106, 1 map, 
32 text figs. Published by the author, Christiansted, Saint Croix, 1917. 
