The Toa Baja Well was drilled on the coastal plains of northern Puerto Rico with a total depth of 2705m [Larue, 1990]. Interstratified limestone, quartz-bearing calcareous sandstones, and shales dominate the uppermost 580 m and are separated from underlying rocks by an unconformity. Below this unconformity continuing tototal depth, lithologies encountered consist of volcaniclastic sandstones/siltstones, pelagic carbonates, volcanic flows and either plutonic rocks or coarse-grained immature sandstones derived from plutonic bodies....