( ( Some pumice ) ( ( ( ( ( ( is ( so light ) ) , ) ( because ( of ( the ( many ( gas bubbles ) ) ) ) ) ) , ) ( that ( it ( floats ( on water ) ) ) ) ) . ) )
(ROOT (S (NP (DT Some) (NN pumice)) (VP (VBZ is) (ADJP (RB so) (JJ light)) (, ,) (SBAR (IN because) (FRAG (PP (IN of) (NP (DT the) (JJ many) (NN gas) (NNS bubbles))))) (, ,) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ floats) (PP (IN on) (NP (NN water))))))) (. .)))
Some pumice is so light, because of the many gas bubbles, that it floats on water.
(ROOT (S (NP (NNP Gas) (NN bubble) (NNS holes)) (VP (VBZ helps) (NP (NP (JJ pumice) (NN float)) (PP (IN in) (NP (NN water))))) (. .)))