One may spend an hour very agreeably on the green summit of Knock Farril. And at almost all seasons of the year a green summit it is,--greener considerably than any other hill-top in this part of the country. The more succulent grasses spring up rich and strong within the walls, here and there roughened by tufts of nettles, tall and rank, and somewhat perilous of approach,--witnesses, say the botanists, that man had once a dwelling in the immediate neighborhood. The green luxuriance which characterizes so many of the more ancient fortalices of Scotland seems satisfactorily accounted for by Dr. Fleming, in his "Zoölogy of the Bass." "The summits and sides of those hills which were occupied by our ancestors as _hill-forts_," says the naturalist, "usually exhibit a far richer herbage than corresponding heights in the neighborhood with the mineral soil derived from the same source. It is to be kept in view, that these positions of strength were at the same time occupied as _hill-folds_, into which, during the threatened or actual invasion of the district by a hostile tribe, the cattle were driven, especially during the night, as to places of safety, and sent out to pasture in the neighborhood during the day. And the droppings of these collected herds would, as takes place in analogous cases at present, speedily improve the soil to such an extent as to induce a permanent fertility." The further instance adduced by the Doctor, in showing through what protracted periods causes transitory in themselves may remain palpably influential in their effects, is curiously suggestive of the old metaphysical idea, that as every effect has its cause, "recurring from cause to cause up to the abyss of eternity, so every cause has also its effects, linked forward in succession to the end of time." On the bleak moor of Culloden the graves of the slain still exist as patches of green sward, surrounded by a brown groundwork of stunted heather. The animal matter,--once the nerves, muscles, and sinews of brave men,--which originated the change, must have been wholly dissipated ages ago. But the effect once produced has so decidedly maintained itself, that it remains not less distinctly stamped upon the heath in the present day than it could have been in the middle of the last century, only a few years after the battle had been stricken.