AuG. 19, 1923 VAUGHAN: STRATIGRAPHY OF THE VIRGIN ISLANDS 307 
Anna Bay (probably meaning Anna Berg). Although paleontologic 
evidence is not available for Saint John, the lithologic characters are 
such as to leave no reasonable doubt of the presence on it of both 
Cretaceous sedimentary and volcanic rocks as on Saint Thomas, which 
is only about one and a half miles from the west end of Saint John, and 
there may be rocks of pre-Cretaceous age. 
Culebra 
Metamorphosed sedimentary rocks composed of reworked voleanic 
constituents were seen in the valley north of San Ildefonso; southwest 
of Swell Bay at altitudes below 200 ft.; on the point of land on both 
the east and west sides of Surf Bay; west and north of Great Harbor; 
and at Playa Sardinos. On the basis of their lithologic characters it 
seems safe to refer these rocks to the Upper Cretaceous. 
Vieques 
The oldest rocks observed on Vieques comprise a trachytic lava 
flow, overlain by limestone conglomerate, over which is an altered 
basalt, which in turn is overlain by hard blue limestone. This expo- 
sure is at Punta Diablo. The dip of the limestone is as high as 60°. 
Bedded rock of shaly or sandy appearance, which is probably water- 
laid tuffy was seen at many places. Because of its lithologic charac- 
ters, its deformation, and its metamorphism, this group of rocks is 
considered of Upper Cretaceous age. 
Eastern Porto Rico 
Examination was made of bedded sandstones and shales, which are 
composed of water-laid volcanic material, in the vicinity of Fajardo - 
and of a folded basalt flow at Cape San Juan. These sedimeiuts and 
their associated igneous rocks, which are cut by great dikes of dolorite, 
would be referred to the Upper Cretaceous according to the criteria 
I have applied in Culebra and Vieques. They evidently represent 
what Hill described as “‘black or other dark-colored basic igneous 
rocks, occurring as tuffs, conglomerates, and sills of hornblende- 
andesite, cut by dikes of diorite.”? Hill found associated with these 
rocks limestone in which he collected fossils that Dr. T. W. Stanton 
identifies as belonging to the Capriniidae and considers representative 
of the Upper Cretaceous. Berkey’s* descriptions of the rocks exposed 
? Hill, R. T., Notes on the forest conditions of Porto Rico: U.S. Dept. of Agriculture, 
Division of Forestry Bull. 25: 14-15. 1899. 
3 Berkey, C. P., Geological reconnaissance of Porto Rico: New York Acad. Sci. Ann. 
26:1-70. 1915. 
