"That's really of no importance," said Uncle Dick. "The term 'mile' means nothing in travel such as theirs. The real unit was the day's work of 'hearty, healthy, and robust young men.' One set of figures is good as the other. "Still, it may be interesting to see how much swifter the Missouri River is than the Father of Waters. From the Gulf of Mexico to the source of the Mississippi is twenty-five hundred and fifty-three miles. Up our river, to where we stand, is just six miles short of that, yet the drop is more than twenty-five hundred feet more. One drops eight and a quarter inches to the mile, and the other nineteen inches to the mile. "But understand, we're talking now of the upper thread of the Mississippi River, and of the Three Forks of our river--which isn't by any means at its head, even measuring to the head of the shortest of the three big rivers that meet here. Now, add three hundred and ninety-eight miles to twenty-five hundred and forty-seven miles. See what you got?" "That's twenty-nine hundred and forty-five miles!" exclaimed John. "Is it that far from the head to St. Louis?" "Yes, it is. And if you took the Lewis and Clark measurements to the Forks it would be thirty-two hundred and forty-seven miles. "And if we took their distances to the place where they left their canoes--that's what they called Shoshoni Cove, where the river petered out for boats--we'd have three thousand and ninety-six miles; two hundred and forty-seven miles above here, as they figured it, and they weren't at the summit even then. Now if we'd take their probable estimate, if they'd finished the distance to the real head of the Missouri, we'd have to allow them about thirty-two hundred and forty-nine miles plus their overrun, at least fifty miles. "Yes, if they'd have gone to the real source, they'd have sworn it was over thirty-three hundred miles to St. Louis, and over forty-five hundred miles to the Gulf. The modern measurements make it forty-two hundred and twenty-one miles. "So, young gentlemen, you can see that you are now coming toward the head of the largest continuous waterway in the world. It is five hundred miles longer than the Amazon in South America, and more than twelve hundred miles longer than the river Nile, in Africa. "Now, Meriwether Lewis did not know as much about all these things as we do now, yet see how he felt about it, at his camp fire, not so far from here: