( ( is ( called stratigraphy ) ) . )
(ROOT (S (VP (VBZ is) (VP (VBN called) (ADVP (RB stratigraphy)))) (. .)))
is called stratigraphy.
(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))) (. .)))