( ( ( The branch ) ( of ( geology ( that ( deals ( with ( ( the correlation ) ( of ( rock layers ) ) ) ) ) ) ) ) ) ( ( ( ( ( is ( known ( as ( stratigraphy ( -LRB- ( or ( ( biostratigraphy ( when ( focusing ( on ( ( the fossils ) ( within ( the layers ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ) ) , ) and ) ( is ( ( an ( important tool ) ) ( of paleontologists ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN branch)) (PP (IN of) (NP (NP (NN geology)) (SBAR (WHNP (WDT that)) (S (VP (VBZ deals) (PP (IN with) (NP (NP (DT the) (NN correlation)) (PP (IN of) (NP (NN rock) (NNS layers))))))))))) (VP (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (NP (NN stratigraphy)) (PRN (-LRB- -LRB-) (CC or) (NP (NP (NN biostratigraphy)) (SBAR (WHADVP (WRB when)) (S (VP (VBG focusing) (PP (IN on) (NP (NP (DT the) (NNS fossils)) (PP (IN within) (NP (DT the) (NNS layers))))))))) (-RRB- -RRB-)))))) (, ,) (CC and) (VP (VBZ is) (NP (NP (DT an) (JJ important) (NN tool)) (PP (IN of) (NP (NNS paleontologists)))))) (. .)))
The branch of geology that deals with the correlation of rock layers is known as stratigraphy (or biostratigraphy when focusing on the fossils within the layers), and is an important tool of paleontologists.
(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))) (. .)))