There is something about the margins of Ireland, as seen on a map, and even more so when these margins are visited, which gives to this island a peculiar rugged aspect. Its northern, western, and southern sides are penetrated by deep bays, and cut into prominent headlands by the force of the waves of the Atlantic; and this erosive power of the ocean has not only added much to the boldness and beauty of its coasts, but has also revealed to us much information concerning its physical structure, and the conditions under which many of its rocky masses were formed.