The major rock types of the Trinidad Mountains of central Cuba are carbonate rocks and schists of presumable Mesozoic age. Both are carbonaceous, yet devoid of fossils. The carbonate rocks comprise limestones (about 90 per cent), brucite limestone, and dolomites.

The brucite limestone contains chloritic mica (sheridanite). The dolomites, despite lenticulation, might serve as marker horizons. Two varieties are noted, one with crystals of black euhedral gypsum, the other without them.

Most widespread of the schists is a carbonaceous chloritic mica schist which alternates with quartz-garnet-mica schist or less commonly grades into epidote or talc schists.

Serpentinites are of two types: a nodular type derived from peridotites, and a fine-grained type (greenstone) derived from microgabbro. The greenstone is older and has been affected by movement of two periods; one (preserpentinization) formed actinolite, the other (postserpentinization) locally developed magnetite-chlorite schist. Other chloritic derivatives include a goethite-chlorite schist and an albite-lawsonite-chlorite schist. The predominant chlorite is clinochlore.

All rocks are isoclinally folded. Cleavage or jointing that might serve to establish overturning is absent. Strike faults are prominent. Transverse faults, because of the lack of traceable units, are difficult to recognize.

The mountains appear to form a gigantic anticlinorium. A continuous band of amphibolite averaging 1200 feet in thickness separates the carbonate rocks and schists of the mountains from diorite and granodiorite to the north. Although thrusting may exist within the mountains, the large northerly directed thrust formerly postulated for the northern boundary is disproved.

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