in Thoreau’s Journal:

It was quite a discovery when I first came upon this brawling mountain stream in Concord woods. Rising out of an obscure meadow in the woods, for some fifty or sixty rods of its course it is a brawling mountain stream in our quiet Concord woods, as much obstructed by rocks – rocks out of all proportion to its tiny stream – as a brook can well be. And the rocks are bared throughout the wood on either side, as if a torrent had anciently swept through here; so unlike the after character of the stream. Who would have thought that, on tracing it up from where it empties into the larger Mill Brook in the open peat meadows, it would conduct him to such a headlong and impetuous youth. Perchance it should be called a “force”. It suggests what various moods may attach to the same character. Ah, if I but knew that some minds which flow so muddily in the lowland portion of their course, when they cross the highways, tumbled thus impetuously and musically, mixed themselves with the air in foam, but a little way back in the woods! that these dark and muddy pools, where only the pout and the leech are to be found, issued from pure trout streams higher up! that the man’s thoughts ever flowed as sparkling mountain water, that trout there loved to glance through his dimples, where the witch-hazel hangs over his stream!