( ( Centuries ( of ( chemical erosion ) ) ) ( slowly ( ( ( ( formed ( these caverns ) ) ( inside ( Humpback Mountain ) ) ) ( when ( ( carbon dioxide ) ( ( ( ( combined ( with water ) ) ( to ( make ( carbonic acid ) ) ) ) and ) ( began ( ( dissolving ( calcium carbonate ) ) ( in ( ( the rock ) ( along ( its course ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (NP (NNS Centuries)) (PP (IN of) (NP (NN chemical) (NN erosion)))) (ADVP (RB slowly)) (VP (VBD formed) (NP (DT these) (NNS caverns)) (PP (IN inside) (NP (NNP Humpback) (NNP Mountain))) (SBAR (WHADVP (WRB when)) (S (NP (NN carbon) (NN dioxide)) (VP (VP (VBD combined) (PP (IN with) (NP (NN water))) (S (VP (TO to) (VP (VB make) (NP (JJ carbonic) (NN acid)))))) (CC and) (VP (VBD began) (S (VP (VBG dissolving) (NP (NN calcium) (NN carbonate)) (PP (IN in) (NP (NP (DT the) (NN rock)) (PP (IN along) (NP (PRP$ its) (NN course)))))))))))) (. .)))
Centuries of chemical erosion slowly formed these caverns inside Humpback Mountain when carbon dioxide combined with water to make carbonic acid and began dissolving calcium carbonate in the rock along its course.
(ROOT (S (NP (NNP Carbon) (NN dioxide)) (ADVP (RB chemically)) (VP (VBP weather) (NP (NNS rocks)) (PP (IN by) (S (VP (VBG creating) (NP (NNS acids)))))) (. .)))