They spent some time around the Rock, examining it, finding the cliff to be about one hundred and fifty feet in height and giving a good view out over the valley plains, over which one could see many miles, and from which the great rock itself could be seen for great distances. "Here was the old ford of the road agents' trail," said Billy. "They crossed here and headed out, east and south, for the hills between here and Virginia City. They were hunting for easier money than beaver then, though--gold! This was the murderers' highway, right by here. Over a hundred men were murdered on this hundred miles." They went back to their encampment and, after their simple preparations were over for the evening, spread out their books and maps once more, John endeavoring laboriously to fill in the gaps of his own map; rather hard to do, since they had not followed the actual stream course on their way up with the pack train. "This Wisdom River, now," said he, "must have been a puzzler, sure enough. That's called the Big Hole to-day. I'll bet she was a beaver water, too, as well as full of trout. Wonder if she had any grayling in her. Here's a town down below here, near the mouth of the Red Rock, called Grayling." "Must have been grayling in all these upper Missouri waters," nodded Billy. "I don't think the _Journal_ mentions them, but they saw whitefish, and the two often go together, though by no means always. The Madison is a grayling stream, or was--the South Fork's good now, and so is Grayling Creek, or was. The headwaters of the Red Rock were full of grayling once. The trouble is, so many motor cars now, that everybody gets in, and they soon fish a stream out." "Shall we get to see a grayling?" asked Rob. "You know, we got the Arctic grayling on the Bell River, in the Arctic regions. They call them 'bluefish' up there. They're fine." "So are these fine. I'd rather catch one grayling than a dozen trout. But they're getting mighty scarce, and I think before long there won't be any left. "But look what a beaver country this must have been!" he added, waving a hand each way. "Fifty by two hundred miles, and then some. No wonder the trappers came. It wasn't long before they and the Blackfeet mixed it, all along in here." "Listen," said Uncle Dick, "and I'll tell you a little beaver story, right out of the _Journal_." "Aw--the _Journal_!" said Jesse. "I'd rather catch one!" "Wait for my story, and you'll see how important a small thing may be that might make all the difference in the world. Now the hero of my story is a beaver. I don't know his name. "Look on your map, just above here--that's the mouth of the Wisdom, or Big Hole, River, that Lewis and Drewyer explored first, while poor Clark, with his sore leg, was toiling up with his boat party, after he was better of his sickness.