David called for the compass.

"We're going to go due west now," he said. "We must mark the map and remember that as long as we follow the stream uphill and as long as this valley runs to the west we must get to the top. Are you two ready? We are really going to start."

For a quarter of a mile the brook wandered through a sloping meadow. The bracken was close to the path which here was only wide enough for them to walk single file. They passed a cottage on the hillside, and then, suddenly, the mountain seemed to come right down to them.

The stream turned away to the left, and when they looked back, the cottage and the pleasant slopes had disappeared and they were in entirely different country. Although the valley was still fairly wide the stream was already narrower and with a rockier bed. On each side the mountain came down steeply, and they could see why the valleys were called gutters. Sometimes the track wandered from the stream to avoid rocks, but it was never far away. A few hawthorns were the only trees, their trunks showing wisps of wool rubbed from the backs of sheep.

This valley was well-named "Dark Hollow."

David soon forgot how many times the path had changed direction, but when they came to their first valley on the south, and their stream's first tributary, he called a halt by a stunted tree.

"We'll rest now for ten minutes. Take your packs off and let's sit on this rock in the sun."

"What about some chocolate?" asked Dickie brightly.

"Save us carrying it any farther," said Mary.

The captain agreed. They munched in silence for a little. Macbeth bolted his share.

David tried to continue his map, but it was difficult to remember what had happened after they had left the cottage. The compass showed that their stream was still running from the west. The "tributary" valley was very wild and lonely without even a path.

"David," said Mary suddenly, "this is a real adventure. I like it."

"The realest we've had," added Dickie. "But I hope we see that old devil."

They had not gone very far after this before the valley narrowed and the sides became steeper. Bracken had given place to heather and bilberries. And all around them was the music of running water.

The stream ran deeper and faster and was still their cheerful guide, but little trickles from the side of the mountain made the ground soft under their feet. The path was steeper, too, and they realized at last that they were really climbing.

The twins were leading and were perhaps fifty yards ahead. David was beginning to find the haversack heavy, and was just wondering whether it might not soon be a good idea to lighten it by Mary's method, when she called out excitedly, "Come quick, David, and see what we've explored. Hurry up!"