Perhaps no country in the world possesses so complete a series, as Ireland, of Domestic Architecture, in the full meaning of the words, that is, of human habitations; it begins with the underground abodes and the beehive houses of the earliest inhabitants of the island (belonging to the same period as the Cromlechs and Cairns), and is continued almost without interruption to our own day. But, before any attempt is made to describe or to classify the existing remains of human dwellings in Ireland, it is necessary to call attention particularly to the geological formation of the country. The nature of the building materials, as is well known, exercises great influence everywhere upon the architectural character, but nowhere else is this so evident and distinct as in Ireland. With a few rare exceptions, such as unfortunately are Dublin and Belfast, and their immediate neighbourhoods, stone is every where abundant, and generally of the same quality, extremely hard and durable, but very- difficult to cut or work in any way. A very large part of Ireland is an immense limestone plain, covered indeed in many places with extensive peat-bogs, but these are seldom very deep; in general the stone is very near the surface, and in many places it crops out. This limestone when broken up, and especially when burnt into lime and mixed with the peat, makes a very fertile soil. In many districts, especially in Galway, the surface is so much covered with loose stones of large size, that they have to be removed before the soil can be cultivated.