The Earliest Inhabitants: The Dynamics of the Jamaican Taino

Blue Schist
The story of Jamaican blue schist is particularly interesting. The rock has a
striking blue colour caused by the mineral glaucophane. This rock currently
has great geological significance as it forms under conditions of low-temperature,
high-pressure metamorphism, thought to exist only at the margins of
lithospheric plates (in terms of current plate tectonic theory). It was previously
known in the Caribbean only in southeast Cuba and the Dominican Republic
but was discovered in Jamaica in 1972 on Union Hill, St Thomas, on the
south flanks of the Blue Mountain Inlier (Draper and Horsfield 1973). This
prominent hill forms the divide between the eastern and western arms of the
Morant River, and sparse pebbles of blue schist occur in the riverbed. They are
very rare on the south-coast beaches. Three celts are composed of this rock,
which almost certainly originated in Union Hill.
Lava
A number of celts are composed of relatively unaltered lava – mostly andesites,
readily recognized by their porphyritic texture of large, well-shaped crystals of
white feldspar and black pyroxene or amphibole, set in a finer-grained
ground-mass. It is not possible to identify the source of the lava as such rocks
are found in all of the inliers of older rocks in Jamaica. They occur either as
ancient lava flows or as pebbles and boulders of lava in the sedimentary rocks,
where they were derived by erosion of the ancient lavas many millions of years
ago. Lava boulders are also abundant in the younger sedimentary rocks of
Jamaica and have a similar origin. It is possible, however, that one day archaeologists
may find a tool with such striking and unusual texture that it can be
matched with its parent lava flow. Several such flows exist; for example, in
the Wagwater River there are pebbles of an andesite lava with abundant
feldspar phenocrysts around 3 cm long. The Swift River in Portland provides
the north-coast beaches with pebbles of another striking andesite, notable for
an abundance of cube-shaped, plagioclase phenocrysts.
Sedimentary Rock
A few axes are composed of the sedimentary rocks sandstone and shale. These
are khaki- or yellow-coloured, and their source cannot be located as they occur
as both younger and older sedimentary rocks across the island. It is surprising
to see tools manufactured from these rocks, for although the coarser sedimentary
grains are composed of lava or hard minerals found in lava, the grains are
P ETROGRAPHY AND S OURCE OF S OME A RAWAK R OCK A RTEFACTS FROM J AMAICA
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