216 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



STRATIGRAPHY OF THE VIRGIN ISLANDS OF THE UNITED STATES AND OF 

 CULEBRA AND VIEQUES ISLANDS 



BY THOMAS WAYLAND VAUGHAN 



i Abstract) 

 The following are the conclusions expressed in this paper : 



(1) The presence of shoal water deposits of Upper Cretaceous age, in Saint 

 Croix and in the islands on the Virgin Bank from Saint John to Porto Rico 

 and in Porto Rico, shows that the major tectonic axis of this part of the 

 West Indies antedates Upper Cretaceous time, because there was an ante- 

 cedent basement on which these deposits were laid down. I have recently 

 suggested that these major trends may be even as old as late Paleozoic. 



(2) During Upper Cretaceous time it is probable that most, perhaps all, of 

 the areas now occupied by land were under water, and that there was con- 

 siderable volcanic activity is proven by the water-laid tufCs and lava flows 

 which are interbedded with the shoal-water calcareous 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 highly metamorphosed. There were also intrusions of diorite, 

 dolerite, and granite, and probably the extrusion of some volcanic rocks. 

 West of the Virgin Islands, there was during later Eocene time extensive sub- 

 mergence in Santo Domingo, Haiti, and Cuba, as is attested by the Upper 

 Eocene limestones now above sealevel 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 

 baselevel the tightly, steeply folded strata of the mountaiiis. 



(5) In Middle Oligocene time a large part of Saint Croix was submerged 

 and, with slight fluctuations, remained under water until some time during 

 the Miocene. Although both the northern and southern, but not the axial, 

 parts of western Porto Rico were submerged 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 limestone 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 south- 

 ern shore and eastern end of Vieques Island; both the northern and the 

 southern edges of the bank were submerged probably by marginal down-flex- 



