is my resolution to find them or some others who have horses if
it should cause me a trip of one month.'

"So that must be the Rock over yonder. We're below the canyon, and below
the Wisdom, and below the Philanthropy, and below the end of the
railroad, and in the third valley. Besides, look at it. Just as sure as
Sacagawea was about it!"

"You're right," said Billy. "That's the Point of Rocks, as it's called
now."

They made down to the edge of the valley and went into camp across from
the great promontory which so long had served as landmark in all that
country. That night all of them forded the river horseback and rode
close to the historic point. Jesse, who was prowling around on foot, as
was his habit, closely examining all he saw, suddenly stooped, then rose
with an exclamation.

"See what I've found!" said he.

"What is it--a gold nugget?" asked his uncle.

"No. An arrowhead. Funny one--looks like it was made of glass, and black
glass at that."

Uncle Dick examined it closely.

"Jesse," said he, "that's one of the most interesting things we've run
across on this whole trip. Did you know that?"

"No. Why?"

"You wouldn't think that arrowhead was going to take you to the true
head of the Missouri, and to good fishing for trout and grayling, would
you?"

"Why, no! How's that?"

[Illustration: JESSE SUDDENLY STOOPED, THEN ROSE WITH AN EXCLAMATION]

"I'll tell you. That's an obsidian arrowhead. The Bannacks and Shoshonis
got that black, glassy stuff at one place--the Obsidian Cliff, in
Yellowstone Park! Those old trails that Lewis saw to the south were
trails that crossed the Divide south of here. They put the Indians on
Snake River waters. These tribes hunted down there. They knew the head
of the Red Rock. They knew the head of the Madison. They knew the Gibbon
River, and they knew the Norris Geyser Basin, up in Yellowstone Park.
It's all right to say the Indians were afraid to go into Yellowstone
Park among the geysers, but they did. They knew the Obsidian
Cliff--close by the road, it is, and one of the features of the Park, as
it now is.

"It's a far shot that arrow will carry you, son. It will show you more
of these Indian trails than even Lewis and Clark ever knew. Of course,
they didn't want to go south; they wanted north and west, because they
knew the latitude and longitude of the mouth of the Columbia River. They
knew that was northwest. They knew any water they got on, once over the
D