Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
bullātĭo, ōnis, f. [bullo], a bubbling, forming of pebbles, of a stone found in small detached fragments: sparsa bullatio magnetis (opp. cautes continua), Plin. 34, 14, 42, § 148 Sill. and Jan. (al. bulbatio).