( ( As ( glaciers ( ( advance and ) retreat ) ) ) ( , ( rock ( ( ( ( ( ( ( is plucked ) , ) transported ) , ) and ) ( deposited ( by ( moving ice ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (JJ glaciers) (NN advance) (CC and) (NN retreat))) (, ,) (NP (NN rock)) (VP (VP (VBZ is) (VP (VBN plucked))) (, ,) (VP (VBD transported)) (, ,) (CC and) (VP (VBD deposited) (PP (IN by) (S (VP (VBG moving) (NP (NN ice))))))) (. .)))
As glaciers advance and retreat, rock is plucked, transported, and deposited by moving ice.
(ROOT (S (NP (DT A) (NN glacier)) (VP (VBZ leaves) (PP (IN behind) (NP (JJ bare) (NN rock))) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ retreats))))) (. .)))
A glacier leaves behind bare rock when it retreats.