In "Heart of Darkness", who said, "Wood for you. Hurry up. Approach cautiously."

Although Marlow doesn't realize it at the time, this message is left for Marlow by the Russian. Marlow knows something is wrong, but is not
sure what. They look into the jungle, but find no clues. In the hut, with a plank on two posts serving as a table and rubbish in a dark corner, he finds a coverless book about seamanship with notes written in a language Marlow does not understand. Finding the book and looking at the notes i are an “extravagant mystery” for Marlow. His quest to save Marlow becomes more urgent.