The way led on through a forest of pines, the trail underfoot being of lava, as hard and smooth as a road could be. They were gradually drawing nearer to Sunset Mountain. After a time they turned off to the right, heading straight for the mountain.
Tad rode back to the Professor to find out where they were going.
"I thought you boys might like to explore the mountain. You will find some things there well worth scientific consideration."
"Yes, sir; that will be fine."
"You know the mountain was once a great volcano."
"How long ago?" interrupted Stacy.
"A few million years or so."
"Mr. Nance must have been a boy in short trousers then," returned Stacy quizzically. The guide's whiskers bristled and stood out straight.
The road by this time had lost its hardness. The ponies' hoofs sank deep into the cinders, making progress slow for the party. They managed to get to the base of the mountain, but the mustangs were pretty well fagged. The animals were turned out for the night after having been hobbled so that they could not stray far away.
"Now each of you will have to carry a pack," announced the guide.
"I will tell you what to take."