( Stratigraphy ( ( is ( ( the study ) ( of ( rock layers ) ) ) ) . ) )
(ROOT (S (NP (NNP Stratigraphy)) (VP (VBZ is) (NP (NP (DT the) (NN study)) (PP (IN of) (NP (NN rock) (NNS layers))))) (. .)))
Stratigraphy is the study of rock layers.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (NP (DT the) (NN study)) (PP (IN of) (NP (NN rock) (NNS layers)))) (ADVP (RB stratigraphy))) (. .)))