natural position. The depth of overlying peat affords no safe criterion for calculating the age of the cabin or village, for I have shown in the 'Principles of Geology' (ch. xlvi.), that both in England and Ireland, within historical times, bogs have burst and sent forth great volumes of black mud, which has been known to creep over the country at a slow pace, flowing somewhat at the rate of ordinary lava-currents, and some times overwhelming woods and cottages, and leaving a deposit upon them of bog-earth fifteen feet thick.
None of these Irish lake-dwellings were built, like those of Helvetia, on platforms supported by piles deeply driven into the mud. 'The Crannoge system of Ireland seems,' says Mr. Wylie, 'well nigh without a parallel in Swiss waters.'
