Through it all, back and forth, like the walls of a labyrinth, run the broken, twisted, faintly defined geological systems, which cross each other so frequently and so vigorously that all semblance of order is lost in the tumultuous upheaval. Here are strata deposited by the miocene tertiary; here are breakings forth of metamorphic rocks of many periods; here are the complex results of diverse influences and forces. Down in the south is a great cavern--of which ninety-seven miles and twenty-five hundred rooms have, at this writing, been explored--which was once the interior of a geyser. For ages it spouted; for ages more its fluids crystallized and petrified into varied and beautiful forms; and then, finally, many layers of stratified rock were slowly overlaid to seal forever this dried-out, beautiful, lifeless mummy of a cave. It lies there now, as it has lain through the centuries, with a single, tiny opening by which it can be entered--a palace of vast re-echoing halls, hung with jewels, a horror-haunted honeycomb of unsounded depths, a solemn abode wherein not the faintest drip of water, not the gentlest sigh of air through the corridors, breaks the eternal silence. Only its mouth roars continually as the winds rush in or out. The Indians assign to it the spirits of their dead warriors, and cannot be induced to approach it. Geologists rave over it, and cannot be persuaded to come away. But this is in the latter day of railroads and tenderfeet. At the time of which this story treats, little was known of the country. It was simply a great second-hand shop, of a little of everything in the geological line. When the party arrived at Spanish Gulch, the doctor was so eager to get into the wonderful hills that only with the greatest difficulty did he constrain himself to help Jim erect a log cabin for the accommodation of his family. Even then he was not of much use, although he could at least help to lift timbers. Jim practically did it alone, and it took him almost a month; but when it was done, it was very nice. The doctor accepted the free gift of the scout's labor and skill quite as a matter of course, just as he had taken the free gift of an ordinarily expensive pilotage across the plains; but the woman appreciated, and perhaps she understood, for she suddenly became very shy in Jim's presence. And then, sometimes, she would gaze at him, when he was not looking, with an adoration of gratitude filling her eyes.