( ( ( ( Beach sands ) and ) ( dune sands ) ) ( ( tend ( to ( ( be well-sorted ) ( because ( ( ( the energy ) ( of ( ( ( the waves ) or ) wind ) ) ) ( ( is usually ) ( rather constant ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Beach) (NNS sands)) (CC and) (NP (NN dune) (NNS sands))) (VP (VBP tend) (S (VP (TO to) (VP (VB be) (ADJP (JJ well-sorted)) (SBAR (IN because) (S (NP (NP (DT the) (NN energy)) (PP (IN of) (NP (NP (DT the) (NNS waves)) (CC or) (NP (NN wind))))) (VP (VBZ is) (ADVP (RB usually)) (ADJP (RB rather) (JJ constant))))))))) (. .)))
Beach sands and dune sands tend to be well-sorted because the  energy of the waves or wind is usually rather constant.
(ROOT (S (NP (NNP Low) (NN energy)) (VP (VBZ causes) (S (NP (NNS waves)) (VP (TO to) (VP (VB bring) (NP (NN sand)) (PRT (RP up)) (PP (IN onto) (NP (NP (DT the) (NN beach)) (PP (IN during) (NP (NNS summers))))))))) (. .)))