And now that modern geology is revealing to us more and more of the origin and structure of the mountain ranges of the world, and telling us more and more of the wondrous materials which go to their building, the field for mysticism is being widely extended. Different, but hardly less powerful, is the influence of hill scenery--whether they "in the distance lie Blue and yielding as the sky," or whether their gentle slopes are climbed and their delicate beauties seen close at hand. As Ruskin has averred, even the simplest rise can suggest the mountain; but it also has a mystic charm of its own, complementary to that of the sheltered vale, which is exquisite alike in its natural simplicity, and in its response to the labours of man, where some "kneeling hamlet drains The chalice of the grapes of God." But though the influence of mountains, hills, ravines, and vales, is obvious even to the superficial enquirer, it should not obscure for us the very real, if less potent influence of lowlands, plains, and deserts. More especially subtle in its effect upon the spirit of man, is the loneliness of wildernesses, the prairies, the pampas, the tundras, the Saharas. The Greek Pan was essentially a god of the wild, unploughed surfaces of the earth. Hence, also, the frequent conjunction of the wilderness and silent meditation and ascetic discipline. Schopenhauer suggests that one secret of the spell of mountain scenery is the permanence of the sky-line. Shall we say that one secret of the solitary place is the turning in of the human spirit upon itself because of the sameness of the permanent sky-line?