Dredge hauls from the West Mariana Ridge recovered vesicular dacitic lava and late Pliocene sandstone from depths between 3000 and 4000 m. The sandstone, consisting of glass shards identical to the dacitic glass and pelagic foram tests, appears to have been deposited contemporaneously with the lavas. The very high vesicularity of the dacite suggests that it was erupted near sea level, implying Quaternary subsidence of the West Mariana Ridge.

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