“Well,” Ace began, “the map of the typical cave, say like Mammoth, wiggles around a little like a river with its tributaries, though nothing like so regularly, with here and there a wider place, and––”
“Here and there,” contributed his chum, “a well to a lower level.”
“Yes. You see, the water that wears a cave out of the softer layers of rock seeps in along the fissures of the surface rock, and at first they make subterranean rivers. Where you find these big springs in the hillsides, they may be the outlets of these underground waterways.”
“I get that, all right,” said Ted.
“Well, then, sometimes these Stygian streams––”
“Keep it up, Professor!” Ted clapped him on the shoulder.
“Huh!—These rivers wear away the soft limestone layer,—if it is this kind of a cave,—’till they come to the harder sandstone. Then the first chance they find to get through the sandstone,—perhaps through a crack made by an earthquake or something,—they go down and wear away a deeper level. Mammoth Cave is on five levels. That leaves the upper galleries dry. Now the one we were on was dry except for the moisture that is always seeping into a cave, but I suspect now we’re on a level with the river, it’s so muddy, and we’ll find it somewhere.”
“Then we’ll find it somewhere!” brightened Ted. “And we can follow it. That’s the plan of action!” and he jumped to his feet.
“We’ll follow it if we can. Thunder! I wish we had a boat.”
“So long as you’re wishing, why don’t you wish for a fat steak with onions?”