as yet really suspecting anything, he walked over to the heap and began to rake the ashes from one side of it with a little stick.  Many of the burned leaves still retained perfectly their shape and outline.  The serrated edges and the feathery veining were distinct in the ashy residues.  They were interesting to see.  Charley continued to level the burned leaves on one side of the pile.  At the touch of his stick they lost their shape and crumbled into formless ashes, even as fairy crystals of snow turn to water beneath a warm current of air.

Suddenly Charley stopped dead still.  Among the ashes turned over by his stick was a long, thin sheet of ash.  Charley looked at it a moment in astonishment.  Then he knew that it was pasteboard.  He sank to his knees on the blackened earth and with his fingers carefully worked in the still warm ashes, raking off the upper layers of leaves gently, so as not to disturb the bottom of the pile.  Carefully he worked, until he had laid bare a long strip of what had been pasteboard.  At his touch this, like the leaves, crumbled.  But one end of it did not disintegrate.  A tiny piece was unconsumed.  From the ashes Charley drew forth a charred bit of greenish pasteboard.  Swiftly but carefully he raked aside the burned pasteboard.  Then he gave a little cry.  On the ground, in the very bottom of the heap, was some candle grease.  His startled exclamation brought Mr. Marlin and Lew running to his side.

“What have you found?” asked the forester sharply.

“A piece of unconsumed pasteboard and some candle grease,” said Charley slowly.  “They were under this mound of burned leaves.”

“We need look no farther for the starting-place of this fire,” said the forester, his face very sober.  “It is just as I suspected.  This fire was of incendiary origin.  Whoever set it, placed a lighted candle inside a pasteboard box, partly filled the box with leaves, heaped some leaves on top of it, and hurried away.  The candle probably burned for hours before it burned low enough to set fire to the leaves.  By that time the culprit was far away and could prove an alibi.”

Charley drew from his pocket the little microscope he used in his class in botany in the high school.  Over and over he turned the scorched scrap of pasteboard, studying it intently.

“The fibers are arranged in a peculiar way,” he said, “and there’s an almost invisible machine marking of a peculiar pattern.  The color of the pasteboard was a dark green.”

The forester took the microscope and examined the charred fragment, handing both, when he had finished, to Lew.

“This is our clue to the incendiary,” he said slowly.  “We must find where pasteboard like that comes from and who had some of it.  Meantime, do not breathe a word of this to any one.  Do not let a soul know that we have discovered how the fire originated.  Let them think we know nothing.  And bear in mind what I told you before:  suspect anybody that circumstances point to, no matter who he is.  Now remember!  Not a soul outside of the three of us must know about this.  We’ve got a long trail ahead of us, but we have at last got a clue.  Sooner or later, if we keep our eyes and ears open and our mouths shut, we’ll find the man who set this forest afire.”