The coast is alive with sea-birds, kittiwakes, razorbills, guillemots, solan geese, puffin, shag, cormorant, and tern; and collections of these birds’ eggs can be obtained at a very small cost in the town. An ingenious provision of Nature saves the eggs from being carried by the raging winds from the ledges of rock on which they are laid, when the mother-bird is not sitting. If, for instance, a guillemot’s egg be looked at, it will be seen that it is so balanced that the wind, catching it, spins it round on its centre of gravity, and does not obtain sufficient resistance to carry it away bodily, and precipitate it into the sea. There are objects of considerable archæological interest in Holy Island, and these are the Cytiau’r Gwyddelod, or habitations of the Irish. There are several collections, and some were explored by the Hon. W. O. Stanley in 1871. They are strewn over the side of Holyhead mountain, but there are others by Porth Dafarch and Mynydd Celyn. The sites of ancient habitations have been selected for shelter from the prevailing winds, and the huts are usually grouped together forming villages of from twelve to fifty huts. They are always protected from hostile attack by rude walls of dry masonry or by precipitous rocks. They are circular, and have slabs of granite set on end to face them within and without. The entrances are to the south. The roofs were constructed of poles resting on the low walls, brought together in the middle, and thatched or covered with turf. The walls of the huts enclose a space of from fifteen to twenty feet in diameter, and the doorway is formed of two upright stones of about four feet high, upon which formerly rested a stone lintel. Some of these huts were dwelling-houses, others served merely as kitchens, and some were sweating or bathing chambers, by the production of steam by throwing water over heated stones. Mr. Stanley found bronze weapons, jet necklaces, ornamented spindle-whorls, stone lamps, and moulds for bronze buttons. The abundance of articles discovered in these dwellings is very unusual and seems to point to their having been left in a hurry. There is a strong camp, Caer-y-Twr, on Holyhead mountain, facing east, and about two-thirds of the way up to the summit from the town. It is surrounded by a rude wall of dry masonry, following the ridge of the rock, which in places is almost perpendicular. The entrance is steep and seems to have been defended by hornwork. There is a narrow cleft in the face of the mountain to the west, above débris of rock that has fallen in some convulsion of nature, leaving a perpendicular face of rock two hundred feet in height. This gap forms a passage through which only one person could pass at a time, and a steep path winds to it between rock faces. It may have served as a postern to the camp.