Ebony spleenwort fern

This morning, a downright cold one—the thermometer stood at 27 when the sun came up—found me leading another walk through the proposed Babcock Ridge preserve. But by the time we started walking, it had warmed considerably. A pair of antlered buck deer were certainly hot and gave us a fine show as the males chased each other no more than 10 yards away from our vantage point. We also managed to uncover a few salamanders. However, when we trekked our way to the top of the ridge, there was no sign of that arboreal Black Rat Snake that had mesmerized us the previous Saturday. In fact, there was very little wildlife at all, so we were left to watch rock walls, glacial erratic boulders, likely serpent and salamander refuges, and ferns—lots of ferns. In general, I'm shaky on Pteridophytes, but I know a few when I see them, and my explorations on Babcock have made it highly desirable to learn more about these ancient plants. Happily, even though I hadn't seen this one in many years, the ID came back to me right away when I spotted a clump growing near an old wall. "Ebony spleenwort," I told the group. "Not particularly rare, but it's a new one for me in this locale." And a curiosity: why here? And why only here?