“Maybe it was there then,” Grove said; “but how do we know it’s there now? Safety first.”

“How can a river move?” he whispered, because one of the librarians had her eye on him.

“That’s all a river ever does,” I told him; “did you ever know a river to stand still?”

So we hunted it up in the Atlas and sure enough, there it was, away up near Alaska and, good night, there was a river named the Dahadinee flowing into it.

“We’ve got the treasure; We’ve got the treasure!” Pee-wee began shouting.

“Shh!” I told him. “Don’t you know you’re in the library? Shhh.”

CHAPTER VI—WE GET NEW LIGHT ON THE MYSTERY

That night Grove and Pee-wee and I hiked over to Harry Donnelle’s house, to show him what we had copied about the poplar that we thought must be the kind of a one that was meant in the letter.

I said, “There isn’t any such tree as the Dahadinee poplar in any of the books, but I think it must be the same as the Mackenzie poplar, because the Dahadinee River is up that way.”

“Sure,” Harry said; “I guess it’s just a nickname for one of those skyscraper pines that you never see south of Canada. I shot a Canada lynx up one of them on Hudson Bay; they puncture the sky, those things.” Cracky, that fellow’s been everywhere.