AuG. 19, 1923 VAUGHAN: STRATIGRAPHY OF THE VIRGIN ISLANDS 315 
because there was an antecedent basement on which these deposits 
were laid down. I have suggested that these major trends may be 
even as old as late Paleozoic. 
(2) During Upper Cretaceous time it is probable that most of, 
perhaps all of, the areas now occupied by land were under water; and 
that there was considerable volcanic activity is proved by the water- 
laid tuffs and lava flows which are interbedded with the shoal-water 
caleareous sediments. 
(3) In early Tertiary, probably Eocene, time there was mountain 
making by folding which in places was so intense that the stratified 
rocks were left in an almost vertical position and both the sediments 
and the older igneous rocks were metamorphosed. There were also 
intrusions of diorite, dolerite, and quartz diorite, and probably the 
extrusion of some volcanic rocks. West of the Virgin Islands, there 
was during later Eocene time extensive submergence in the Dominican 
Republic, Haiti, and Cuba, as is attested by the Eocene formations 
now above sea-level in those areas. 
(4) The episode of mountain making was followed in the Virgin 
Islands by one of prolonged subaerial erosion, and the production 
of the Virgin Bank apparently may in large part be assigned to this 
period of the history of the region. It seems that the axial islands 
on the Virgin Bank and the Central Sierras of Porto Rico, from its 
east to its west end, have continuously stood above the water since the 
close of Cretaceous deposition. In Saint Croix by middle Oligocene 
time erosion had proceeded far enough to reduce almost to base level 
the tightly, steeply folded strata of the mountains. 
(5) In middle Oligocene time a large part of Saint Croix wes sub- 
merged and, with slight fluctuations, remained under water until 
sometime during the Miocene. Although both the northern and 
southern, but not the axial, parts of western Porto Rico were sub- 
merged in middle Oligocene, and probably in lower Oligocene time, 
the eastern end of Porto Rico and the axial islands of the Virgin Bank 
west of Anegada Island were not submerged. The age of the lime- 
stone on Anegada Island is not known. These facts mean that there 
was differential movement, the movement being greater toward the 
west than in the central part of the bank. In lower Miocene time the 
northern shore of Porto Rico east of San Juan was submerged as were 
also the southern shore and eastern end of Vieques Island—both the 
northern and the southern edges of the bank were submerged probably 
by marginal down flexing. Although there are corals in the exposed 
sediments of Oligocene and Miocene age, and corals were therefore 
constructional agents during those epochs, their work as compared with 
