( ( According ( to ( ( the law ) ( of superposition ) ) ) ) ( , ( ( ( ( ( the ( bottom layer ) ) , ) ( ( called simply ) ( ( the lava ) ( flows ( below ( the ( yellow tephra ) ) ) ) ) ) ) , ) ( ( must ( be ( the oldest ) ) ) . ) ) ) )
(ROOT (S (PP (VBG According) (PP (TO to) (NP (NP (DT the) (NN law)) (PP (IN of) (NP (NN superposition)))))) (, ,) (NP (NP (DT the) (JJ bottom) (NN layer)) (, ,) (VP (VBN called) (ADVP (RB simply)) (SBAR (S (NP (DT the) (NN lava)) (VP (VBZ flows) (PP (IN below) (NP (DT the) (JJ yellow) (NN tephra))))))) (, ,)) (VP (MD must) (VP (VB be) (NP (DT the) (JJS oldest)))) (. .)))
According to the law of superposition, the bottom layer, called simply the lava flows below the yellow tephra, must be the oldest.
(ROOT (S (S (NP (NP (JJ Deeper) (NNS layers)) (PP (IN of) (NP (NN rock)))) (VP (MD must) (VP (VB be) (ADJP (ADJP (JJR older)) (PP (IN than) (NP (NNS layers)))) (ADVP (RBR closer) (PP (TO to) (NP (DT the) (NN surface))))))) (, ,) (NP (DT this)) (VP (VBZ is) (NP (NP (DT the) (NN law)) (PP (IN of) (NP (NN superposition))))) (. .)))