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198 having been embedded in a cairn or tumulus—as was the case of the entire group in the Drenthe of which some fifty still remain in a fairly well-preserved condition—some archæologists maintain that this was the original condition of all of them. The theory also derives support from the fact that throughout the whole area of their distribution many are to be seen in all stages of denudation.

The covered-up dolmens and tumuli vary much in size, ranging from that of an ordinary barrow a few yards in diameter up to Silbury Hill, which is 130 feet in height and over 500 feet in diameter at the base. They also vary in appearance owing to the growth of vegetation, and other surface changes.

The larger chambered cairns and tumuli had entrance passages generally constructed of flags set on edge, characteristic specimens of which have been recorded at Uley (Gloucester), Stoney Littleton (Somerset), Park Cwn (Gower Peninsula), Achnacree (and other cairns in the counties of Argyll and Inverness), the Horned Cairns of Caithness, Maeshowe (Orkney), etc. But between dolmens, cairns, tumuli, barrows, etc., there is sometimes no clear distinction, so much do they overlap in constructive details.

No megalithic chamber, or entrance passage, has been discovered in Silbury Hill, and therefore it remains a tumulus. But at one time Minning Low (Derbyshire) was a large truncated cone, 300 feet in diameter and