( ( A ( fossil mold ) ) ( ( is ( formed ( by ( ( the impression ) ( ( left ( in rock ) ) ( by ( ( the remains ) ( of ( an organism ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ fossil) (NN mold)) (VP (VBZ is) (VP (VBN formed) (PP (IN by) (NP (NP (DT the) (NN impression)) (VP (VBN left) (PP (IN in) (NP (NN rock))) (PP (IN by) (NP (NP (DT the) (NNS remains)) (PP (IN of) (NP (DT an) (NN organism)))))))))) (. .)))
A fossil mold is formed by the impression left in rock by the remains of an organism.
(ROOT (S (NP (DT A) (NN mold)) (VP (VBZ is) (NP (NP (DT an) (NN imprint)) (PP (IN of) (NP (NP (DT an) (NN organism)) (VP (VBN left) (PP (IN in) (NP (NN rock)))))))) (. .)))