Huck/Jim Encounter 11 - Chapter 18

After the collision between the raft and the riverboat, Jim and Huck are separated, and don't reunite until well into the Grangerford-Shepardson story.
Also, Hearn notes that there was a long break between chapter 16 and 17, and the story has shifted from a river adventure with Jim to a series of stories about those who live in the towns along the river.