Ten new gravity stations on St. Thomas and 21 stations on St. Croix have been established with the Frost geodetic gravimeter. With new submarine gravity stations made in this area with the Vening Meinesz pendulum apparatus, a 200-km profile is formed across the Virgin Islands. Charts are presented showing simple Bouguer anomalies on land and free-air anomalies at sea.
On St. Thomas, contours of the simple Bouguer anomalies are essentially parallel to the strike of the surface structures. On St. Croix, the contours outline the Tertiary sedimentary basin (Cederstrom, 1950). Estimates from the gravity data indicate that these sediments form a wedge which reaches its greatest thickness, about 2 km, near the eastern margin of the basin.
Seismic stations near the gravity profile are used as a guide in computing a structure section across the Virgin Islands. The M-discontinuity is determined by gravity computations to be at about 29 km beneath St. Thomas and St. Croix and 22 km below sea level under the Anegada trough.