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While on the drift-covered lowlands such cairns are frequently formed of clay, here on the hill-top they are formed entirely of local limestone, which is a splintery rock with much chert irregularly disposed No doubt as originally built they were constructed of blocks such as a man could lift conveniently. But three to four thousand years exposure to heat and cold, rain and frost, have shattered the already splintery boulders, so that the carns are now mounds formed to a considerable extent of material like coarse road metal, with large blocks between, material difficult to excavate, being too coarse and interlocked for spade work, and too much broken up for convenient pitching by hand.

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