It is because I have spent the greater part of my life in studying the architecture of all nations, and through all ages, that I believe myself entitled to express an opinion on the perplexed questions connected with megalithic remains, though it differs widely from that generally received, and that I dare to face the objection which is sure to be raised that my work is based on too narrow an induction, and that I have overlooked the evidences of primæval man which exist everywhere. It is not, however, that I have neglected either the evidence from the drift, or from the caves, but that I have rejected them as irrelevant, and because I can hardly trace any connexion between them and the megalithic remains, to the investigation of which this work is specially devoted. I have also purposely put on one side all reference to hut circles, Picts' houses, brochs, and other buildings composed of smaller stones, which are generally mixed up with the big stone monuments. I have done this, not because I doubt that many of these may be coeval, but because their age being doubtful also, it would only confuse and complicate the argument to introduce them, and because, whenever the age of the great stones is determined these minor monuments will easily fit into their proper places. At present, neither their age or use throws any light either for or against that of the great stones. It need hardly be remarked, to anyone who knows anything about the subject, that the difficulties in the way of writing such a book as this are enormous, and I do not believe any one could, in a first edition at all events, avoid all the pitfalls that surround his path. The necessary information has to be picked up in fragments from some hundreds of volumes of travels, or the Transactions and Journals of learned Societies, none of which are specially devoted to the subject, and very few of which are indexed, or have any general résumé of their contents. Add to this that the older works are all untrustworthy, either from the theories they are twisted to support, or from bad drawing or imperfect knowledge; and too many of the modern examples are carelessly sketched and still more carelessly engraved. Another source of difficulty is, that it is rare with readers of papers and writers in journals to quote references, and sometimes when these are given they are wrong. I have thus been forced to limit the field from which my information is taken very considerably. I have tried hard to introduce no illustration I could not thoroughly depend upon, and I have not intentionally quoted a single reference I had not verified from the original authorities.