The huge concave of the rocky wall towering above them threw the woman's scream far into the vast profound of the ca on. It came sharp to the man's ear, yet terminated abruptly; as when two rapidly moving trains pass, the whistle of one is heard shrill for one moment only to be cut short on the instant. Brief as it was, however, the sound was sufficiently appalling; its suddenness, its unexpectedness, the awful terror in its single note, as well as...