Rocks dredged from 16 localities withing the Cayman Trench suggest a crustal sequence identical to that reported from the mid-oceanic ridge. Serpentinites, serpentinized peridotites, cumulate mafic rocks, and gabbros crop out deep along the precipitous north-trending ridges. Numerous basalts and dolerites crop out somewhat higher, along with minor amounts of limestone and sediment. Major-element variations and trace-element abundances substantiate the abyssal tholeiitic nature of the basalts and indicate possible shallow fractionation from a primary melt in the upper mantle. A combination of dynamic, hydrothermal, and contact metamorphism near the axial valley is proposed to explain the observed metamorphic features. The geochemical data, along with pubulished geophysical evidence, support the hypothesis of a mid-Cayman spreading center in this tectonically complex region.