After the clanking ceases, the Narrator reports that he "resumed the trowel, and finished without interruption the fifth, the sixth, and the seventh tier." The word trowel in this case could be seen as the use of the rhetorical device synecdoche. "Trowel" qualifies as the substitution of a part of or a substance for a whole, one thing for another, or a specific name used for a generic thing. The noun trowel substitutes for the action of using the trowel to complete the building up of the wall. Inother words, instead of saying, "I resumed my work of using the trowel to build the wall," Montresor uses synecdoche to say the same thing by using trowel as a representative word: trowel represents an entire action and process.
The context of this quotation is that after successfully luring the inebriated Fortunato into the niche of the crypt, the narrator--Montresor, the first person narrator--of Edgar Alan Poe's "The Cask of Amontillado" begins to execute his predetermined plan to wall up his enemy. After completing the fourth tier of what would become Fortunato's tomb, Montresor rests and listens to the "furious vibrations of the chain" that he used to lock Fortunato to the granite wall when he was intoxicated less than aware of what was happening to him.