( It ( ( is ( ( a ( circular piece ) ) ( of ( ( continental rocks ) ( surrounded ( by ( oceanic crust ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (NP (NP (DT a) (JJ circular) (NN piece)) (PP (IN of) (NP (NP (JJ continental) (NNS rocks)) (VP (VBN surrounded) (PP (IN by) (NP (JJ oceanic) (NN crust)))))))) (. .)))
It is a circular piece of continental rocks surrounded by oceanic crust.
(ROOT (S (NP (NNP Gabbro)) (VP (VBZ is) (NP (NP (DT a) (JJ dark) (JJ dense) (NN rock)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (VP (VB be) (VP (VBN found) (PP (IN in) (NP (DT the) (JJ oceanic) (NN crust)))))))))) (. .)))
Gabbro is a dark dense rock that can be found in the oceanic crust.