[Footnote 41: Laing in his wrath seems to have, by accident, very nearly guessed the truth, when, refuting the authenticity of Ossian, he accuses Macpherson of "having rendered the Highlanders a race of unheard-of infidels, who believed in no Gods but the ghosts of their fathers."] CHAPTER II. PRELIMINARY OBSERVATIONS. Before attempting to examine or describe particular instances--in which, however, the main interest of the work must eventually be centred--it would add very much to the clearness of what follows if a classification could be hit upon, which would correctly represent the sequence of forms. In the present state of our knowledge such an arrangement is hardly possible, still the following 5 groups, with their sub-divisions, are sufficiently distinct to enable them to be treated separately, and are so arranged as roughly to represent what we know of their sequence, with immense overlappings, however, on every joint. I.--TUMULI _a._ Or barrows of earth only. _b._ With small stone chambers or cists. _c._ With megalithic chambers or dolmens. _d._ With external access to chambers. II.--DOLMENS _a._ Free standing dolmens without tumuli. _b._ Dolmens upon the outside of tumuli. III.--CIRCLES _a._ Circles surrounding tumuli. _b._ Circles surrounding dolmens. _c._ Circles without tumuli or dolmens. IV.--AVENUES _a._ Avenues attached to circles. _b._ Avenues with or without circles or dolmens. V.--MENHIRS _a._ Single or in groups. _b._ With oghams, sculptures, or runes. TUMULI. The first three of the sub-divisions of the first class are so mixed together that it is almost impossible in the present state of our knowledge to separate them with precision either as to date or locality, while, as they hardly belong to the main subject of this book, it will not be worth while to attempt it here.