( ( ( rock , ) ( ( ( ( ( sand , ) silt ) , ) and ) ( organic particles ) ) ) . )
(ROOT (NP (NP (NN rock)) (, ,) (NP (NP (NN sand)) (, ,) (NP (NN silt)) (, ,) (CC and) (NP (JJ organic) (NNS particles))) (. .)))
rock, sand, silt, and organic particles.
(ROOT (S (NP (NP (NNS Particles)) (PP (IN of) (NP (NN sand) (CC and) (NN rock)))) (VP (VBP are) (VP (VBN carried) (PP (IN by) (NP (JJ longshore) (NN drift))))) (. .)))