These ferns were rooted in the moss on the north side of a large boulder in Shakerag Hollow.
The fronds arch through the air and, when they are fully grown, their skinny ends touch down into the moss…
…and root, producing a new fern, a clone of the parent. This baby will ultimately grow into an independent individual, arch its own fronds outward, and continue the “walk” across the boulder.
Walking ferns need a moist carpet to take root and they are seldom found away from thick mossy mats. Unfortunately their diminutive charm makes them attractive to plant-thieving gardeners. Transplants seldom survive, so it is best to leave them unmolested in the woods.
David George Haskell 
One of my favorite ferns. And they like moss carpets atop limestone rocks, almost exclusively, if I’m correct. That’s why you see them mostly in the limestone stratum at Shakerag and elsewhere on the Plateau, and not among the sandstone rocks. Gardeners of the thieving variety almost never realize that, as far as these highly specialized species are concerned, it’s almost impossible to duplicate in the garden the exact conditions necessary for these plants to survive.
I’m always delighted to find walking ferns and I’m glad to know that they bring pleasure to you also. Thanks for this comment. Agreed — except for the exclusive use of limestone. There are some colonies on thickly mossed sandstone in several spots around Sewanee, including the one in this post. So, I guess their substrate requirements are more catholic than usually noted. You’re right about gardens — not many can replicate the moisture and shadiness of these north-facing coves.