The systematic exploration of lacustrine habitations in the latter half of the nineteenth century has achieved remarkable success; and the results are among the most satisfactory in the whole field of archæological investigation. Water--usually a destructive element--has, in the case of lake-dwellings, so far preserved these remains of early races that we are enabled to learn much of their habits and modes of life, of which we could otherwise glean but little knowledge. Man has at all times familiarised himself with water; and he readily adapts himself to the conditions of dwelling near or upon it, whenever he adopts it as a surrounding for his home. Primitive man saw easily that islands afforded a safe retreat in the great struggle for existence between him and his natural foes--man and beast. In selecting water, where islands did not exist he created them for himself, and brought considerable mechanical skill and ingenuity, and immense labour, to bear upon their construction. To hollow out a log-canoe, and to make an artificial island with trunks of trees, branches, stones, and earth, were but stages, though greatly advanced ones, in the development of human intelligence from its low condition in the cave-dwellers and men of the river-drift. It is evident, however, that these artificial islands had been long used in Europe before they had been adopted in Ireland as dwelling-places. Many a desolate moorland district, and many a shallow waste of water, throughout Ireland, now showing no other signs of animal life than the wild fowl which frequent them, were at one time the sites of human habitation, industry, and even art of no mean character. A slight elevation on the surface of a bog, some bleached sprays of birch, ash, or sallow, or the appearance of a few grey or white reed-surrounded stones, rising a few inches above the surface of a lough, will often, to the practised eye, indicate the position of a _Crannog_, by which name lake-dwellings in Ireland are usually designated. It is, however, to turf-cutting operations, or to drainage, that the discovery of the great majority of these interesting sites must be attributed. The term ‘Crannog’ is derived from _crann_, a tree; but whether it was given originally to the wood used in constructing the island, or to the huts, cannot now be determined. [Illustration: Lake-dwellings in Lough Eyes, Co. Fermanagh.]