To get to the valley, Tommo and Toby must go down another ravine and spend all day doing so. It's hard going, and they camp for the night. It's been four days since they left the ship.
The next day, they continue down the ravine, only to encounter an abyss with a hundred-foot drop. Despairing, Tommo believes it's impossible to keep going. But Toby is less easily discouraged. He figures out a system of swinging from root to root.
When they get to the bottom, they realize that the bottom of the abyss ends in a sheer drop-off, and at Toby's encouragement (total surprise, right?), they jump from the abyss to the adjacent tree-tops, shimmying down the trees and onto safe ground below.
That night, they sleep. When they wake they hear a nearby waterfall, which they hope will lead them to the valley. It's more bad news, however, as they see that the waterfall goes another 300 feet down into the valley. They'll have to find some way to follow it.
Unsure of what they'll do next, they sleep restlessly and poorly.
Then Tommo pushes forward. "I will not recount every hair-breadth escape, and every fearful difficulty [...]," he explains, saying that after five days they at last find themselves in the valley.