Within a predominantly pyroclastic succession are small-scale intrusive bodies and more extensive pillow lavas and pillow lava breccias of andesitic composition. Sedimentary structures in the vitric rhyolitic tufts intruded by magma, suggest contemporaneous deposition and intrusion. This seems to indicate that intrusion was close to the sediment-water interface. The juxtaposition of basic lavas and tuffs with the contemporaneous products of rhyolitic explosive activity is interpreted as evidence for a deep-water depositional environment, into which the bulk of the acid tufts were introduced by mass transport.

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