An appositive
functions as the indirect object of a verb
replaces a noun or a pronoun
indicates which one or what kind
identifies or renames another noun or pronoun

"the sandy walls seemed to collapse in on themselves"

and

"the bloodshot waters seemed to have no bottom"

voracity is the noun corresponding to the adjective voracious, which means (1) eager to consume a great amount of food, or (2) marked by an insatiable appetite. veracity is far more common than the rare voracity, so the latter is sometimes used in place of the former.