Eastern Montana was mostly a shallow inland ocean, almost a swamp with huge forests lining it's shores and islands of volcanoes spewing forth lava to entomb parts of the forest in lava and ash .
(Eastern Montana; was mostly; a shallow inland ocean) (huge forests; lining; it's shores and islands of volcanoes) (volcanoes; spewing lava; to entomb parts of the forest in lava and ash)
Eastern Montana huge forests volcanoes
was mostly lining spewing lava
a shallow inland ocean
it's shores and islands of volcanoes
to entomb parts of the forest in lava and ash