"An isolated fragment of rock, which fell vertically through the water column into finer-grained water-deposited sedimentary rocks. Drop stones range in size from small pebbles to boulders."^^ . _:b1218252 . "ENVO"^^ . _:b1218252 . . "2010-03-20T06:25:06Z"^^ . _:b1218252 . "ENVO:01000136"^^ . "drop stone"^^ . "Dropstone"^^ . . _:b1218252 .