It is probable that these structures were connected with primitive forms of worship, but Sir Norman Lockyer has endeavoured to show, in one of the most fascinating chapters of archaeological research, that the circles and avenues, and the monoliths or menhirs connected with them, were in all probability set up as rough astronomical instruments for observing the rising of the sun or of particular stars, in order to regulate the true length of the year. It is even possible, he contends, to form some idea of the date of their erection. Thus the two avenues at Merivale were probably laid out at different times, one about 1610 B.C., and the other about 1420 B.C., in order to watch the sunrise in May, which was then regarded as the first month of the year; while the avenues at Challacombe, among the most remarkable of all the monuments, are probably of far older date, perhaps 3500 B.C., and seem to have been arranged for the observation of sunrise in November, a month long accepted by some Celtic tribes as marking the beginning of the year. Kistvaens, of which nearly 100 have been found, almost all of them on Dartmoor, are small stone burial chambers, generally used for the reception of the burnt ashes of the dead, probably in many instances originally covered with earth, and made of four slabs of granite set on edge, forming a sort of vault, with another and more massive stone laid on the top. Specially good examples have been found at Fernworthy, on Lakehead Hill, and at Plymouth. The most remarkable kistvaen--belonging, however, to a later period, when burial had displaced cremation--was that discovered on Lundy, containing a human skeleton eight feet two inches in length. Tumuli or burial mounds, called cairns when they are made of small stones, and barrows when they are merely piles of earth, are to be seen in all parts of Devonshire, especially on high ground, sometimes alone, sometimes in groups of from two to ten or twelve, and always round. No long barrows have been discovered in the county. The men of the Bronze Age reached a much higher stage of civilisation than their stone-using predecessors, and very fine examples of their bronze swords, daggers, spear-heads and axes; of their pottery, some of it finely decorated; and of their ornaments, including beads of shale and clay and amber, and an amber dagger-hilt with studs of gold, have been found at various places in Devonshire.