“I—­I don’t exactly understand,” said Lew hesitatingly.

“It’s like this,” said the stranger.  “The forest floor is like a great sponge.  The decayed leaves and twigs are so light and porous that they soak up most of the rain as it falls and hold the water indefinitely.  That keeps the springs full, and the springs feed the brooks, and so there is water all the year round.  It is nature’s method of storing up water.  When a fire sweeps through the forest, especially such awful fires as have gone through this valley, the leaves and twigs above ground are burned, and even the roots and the decaying vegetable matter under the earth are consumed.  Nothing is left but mineral matter—­particles of rock, stones, sand, and the like.  The rain will no longer sink into the ground, nor will the earth hold the water as the rotting leaves do.  Then when it rains, the water runs off as fast as it falls.  The brooks are flooded for a few hours and then they dry up until another rain comes.  So you see I meant exactly what I said.  This trout-stream was burned up by the forest fires.  Likewise many of the trout were burned up with it, for in places the fire made the water hotter than trout can stand.  Thousands of them were literally cooked.”

For a while both boys were silent.  The idea was a new one to them.

Presently Charley spoke.  “I knew that fire burned up our timber,” he said, “but I never thought about its burning up our water, too.  I know we’re getting awful short of lumber.  Is there any danger of our running out of water?  But that can’t be, surely.”

“It surely can be,” said the stranger.  “I judge you boys have been here
before, and-----”

“We have,” interrupted Lew.

“Then you know what a magnificent stream this run used to be.  Look at it now.  I don’t believe there is one-tenth as much water in it as there used to be.  Suppose all the mountains in this state should be devastated like this valley.  Where would the towns and cities get their water?”

“Great Caesar!” said Lew.  “I never thought of that.  There wouldn’t be any water for them to get.  If the brooks dried up, the rivers would dry up, too.  Why—­why—­what in the world would we do?  There wouldn’t be any water to drink or wash in or cook with or run our factories.  Why, great Caesar!  If the forests vanished, I guess we’d be up against it.  I never thought of the forests as furnishing anything but lumber.  And I never thought much about that until we tried to buy a little lumber the other day and the dealer wanted ten dollars for half a dozen boards.”

“Exactly!” said the stranger.  “That’s the price you and I and the rest of us in Pennsylvania pay for allowing our forests to be destroyed.”

“They haven’t all been destroyed,” protested Lew.

“No, but the greater part of them have been.”

“You don’t mean really destroyed, do you?” asked Lew.

“Yes, sir.  Absolutely destroyed.  You came up this valley, didn’t you?”