In one respect I cannot but feel that I may have laid myself open to hostile criticism. On many minor points I have offered suggestions which I do not feel sure that I could prove if challenged, and which, consequently, a more prudent man would have left alone. I have done this because it often happens that such suggestions turn the attention of others to points which would otherwise be overlooked, and may lead to discoveries of great importance; while if disproved, they are only so much rubbish swept out of the path of truth, and their detection can do no harm to any one but their author. Whatever my shortcomings, I am too much in earnest to look forward with any feelings of dismay to such a contingency. Besides the usual motives which prompt the publication of such a work as this, there are two which seem to render its appearance at this time particularly desirable. The first is to promote enquiry by exciting interest in the subject; the second is to give precision to future researches. So long as everything is vague and mythical, explorers do not know what to observe or record: this work, however, presents a distinct and positive view of the age or use of the megalithic remains, and every new fact must tend either to upset or confirm the theory it seeks to establish. With this view, I need hardly add that I shall be extremely grateful for any new facts or additional sources of information which may be communicated to me, either through the public press or privately. Numerous persons having local experience must know many things which may have escaped me. It is very probable that these may induce me to modify some of the details of this work; but so much is now known, and the field from which my inductions are gathered is so wide, that I have no fear that they will touch the main arguments on which the theory of this work is founded.[1]