Latour and Jacinto get back on the road to retrieve the sick Father Vaillant. While they travel, they're caught in a sudden snow squall.
Jacinto leaps off his mule and tells Latour to follow him into a deep hole in some nearby rocks.
There is an opening in the rocks that looks like two big stone lips (hence the title of the chapter). Inside the rocks is a cavern with a very high ceiling that's shaped like a religious chapel.
Now that they're inside the cavern, Jacinto seems to realize that he was never supposed to bring a white man to this place. He makes Latour promise to forget it as soon as they leave.
Latour hates the creepy feeling that the place gives him and figures that the sooner he can forget it, the better.
While they're in the cavern, though, Jacinto might as well show Latour around. He even gets Latour to put his ear to the floor of the cavern so he can hear a rushing underground river.
Jacinto lights a fire and the two of them go to sleep in the cavern for the night. While pretending to sleep, Latour catches Jacinto sneaking back to a crack in the rock floor and listening to the underground river.
The next morning, Latour and Jacinto clamber back out into the open. Their mules are totally gone. The two of them walk eight miles to a person's cabin, rent a couple of horses, and continue on.
By the time they reach Father Vaillant's house, the guy's fever has already broken and he's on the road to recovery. It also looks like Latour's buddy, Kit Carson, is there by his side. Carson ends up helping to bring Vaillant back to Santa Fe with Latour.
From time to time, Jacinto's special cave keeps flashing into Latour's mind, although Latour never mentions it to anyone.
After returning to Santa Fe, Latour visits a trader named Orchard and asks him whether the story about the undying Native fire (which Jacinto told him) is really true. Orchard assures him that it is. They also have discussions about whether the Natives feed some of their children to a giant snake.
Orchard says he's not so sure about this, but what he is sure of is that the Native Americans will never let go of their old beliefs. They might accept new ones too, but they'll always hold onto their old ones.