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76 and bones) "were the only implements with which men knew how to furnish themselves," but also that the antiquary has found "clear evidence of such a period."

Moreover, as already mentioned, the Stone Age falls into two distinct periods, the oldest of which, or Palæolithic, will be dealt with in subsequent chapters.

So far as the Neolithic, or more recent Stone Age, is concerned, our knowledge is derived principally from four sources, to the consideration of which I propose to devote four separate chapters: namely, the Tumuli, or ancient burial-mounds; the lake-habitations of Switzerland; the Kjökkenmöddings, or shell-mounds, of Denmark; and the Bone-caves. There are, indeed, many other remains of great interest, such, for example, as the ancient fortifications, the "castles" and "camps" which crown so many of our hill-tops; and the great lines of embankment, which cross so many of our uplands, such as Offa's Dyke and the Wans Dyke; there are the so-called Druidical circles and the vestiges of ancient habitations; the "Hut-circles," "Cloghauns," "Weems," "Pen-pits," "Picts' houses," etc. The majority of these belong, however, in all probability, and many of them certainly, to a later period; and in the present state of our knowledge, we cannot say which, or how many, are referable to the Stone Age.

Flint was the material most commonly used, but every kind of stone, hard and tough enough for the purpose, was utilized during the Stone Age in the manufacture of implements. The magnificent collection of celts at Dublin has been specially studied, from a mineralogical point of view, by the Rev. S. Haughton, and the results are thus recorded by Wilde:

"Of the better qualities of rock suited for celt-making, the type of the felspathic extreme of the series of trap rocks is the pure felstone, or petrosilex, . . . of a pale blueish or greyish green, except where the surface has been acted upon, and the average composition of which is 25 parts quartz and 75 felspar. Its physical characters