On the theory of the introduction of metallurgic arts assumed here, not altogether without evidence, it is not requisite that we should conceive of the aboriginal Caledonians disturbed by the invasion of foreign tribes armed with weapons scarcely less strange to them than those with which the Spanish discoverers astonished the simple natives of the New World. The changes, however, already noted in the forms and modes of sepulture, the abandonment of the long barrow, the introduction of cremation, of the sitting or folded posture of the dead with the correspondingly abbreviated cist, and of a uniform and defined direction of laying the dead, are all suggestive of the probable intrusion of new races in earlier as well as in later times. The facilities afforded by the more pliable metal tools would speedily work no less remarkable changes on the mansions of the living than on the sepulchres of the dead. The subterranean weem would give place to the wooden structure, which the new arts rendered at once a more convenient and simpler style of architecture; while the inroads on the forests which such changes led to would necessitate the clearing of the neighbouring lands preparatory to the extended labours of the agriculturist. To the same cause also we may probably trace the origin of many of those extensive tracts of bog and peat-moss which still encumber the limited level areas of Scotland. The wasteful profusion of the natives of a thinly peopled country would lead to the destruction of the forests with little heed to aught but the supply of their own immediate wants. In the extensive mosses of Kincardine and Blair-Drummond, which have yielded such valuable archæological relics, when the surface of the underlying clay was exposed by the removal of the moss, it was in many places covered with trees, chiefly oak and birch, of a great size. These were found lying in all directions beside their roots, which continued firm in the ground in their natural position; and from impressions still visible it was evident that they had been cut with an axe or some similar instrument.[269] The like discoveries in other Scottish mosses prove their origin from the same wasteful inroads of early times. The occupants of the country at this period were necessarily isolated tribes and clans, with no common interest, and little peaceful intercourse. The arts were therefore practised as in their primeval dawn described by Milton, when the artist formed "First his own tools, then what might else be wrought."