“What else would it be?” Purdick asked.
“I’m not much of a geologist,” Larry returned, “but we all know this: that every mineral vein in the world was once just a crack in the rocks that got filled up at some later time with gangue matter and mineral-bearing stuff. It just occurred to me to wonder if this isn’t one of the cracks that failed to get filled up—in this part of it, at least.”
“You couldn’t tell,” Dick put in.
“No; not positively, of course. But I believe I’m right, just the same. This wall rock doesn’t show any trace of water-wearing. It’s as clean as if the crack had been split open only yesterday.”
Dick laughed. “Let’s make the geology a little more practical and go on. I’d like to see how far this thing extends, and what makes the warm wind.”
Their passage through the crevice was unobstructed for quite a considerable distance. Slowly the daylight from the crack-like opening in the ravine bottom receded, growing fainter and fainter until at length it disappeared entirely and they were dependent upon the candle to light their way. And still the crevice held on, going deeper and deeper into the mountain, narrowing in some places to tunnel width, and then widening out again into a spacious corridor.
They had gone possibly a quarter of a mile from the ravine entrance, though in the silence and darkness it seemed like a much greater distance, when Larry called a halt.
“Hold up a minute, fellows,” he cautioned. “We’re getting too far away from our base of supplies. After what we found out this morning, it won’t do to leave the jacks and all our belongings sticking around where anybody can pick them up and walk off with them.”
“Gee! I forgot all about that,” said Dick. “Let’s hurry back. Maybe those crooks have cleaned us out already!”
Purdick had the candle at the moment and was digging with the pick end of the geologist’s hammer at a soft streak of something in the left-hand wall.