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Show 152 GREAT STONES CrrAP. IlL but its upper surface was now on a level with the surrounding turf. When the stone was removed, an e~act cast of its lower side, forming a shallow crateriform hollow, was left tho inner surface of which consisted J of fine black mould, excepting where tho 1nore protuberant parts rested on the brickrubbish. A transverse section of this stone, together with its bed, drawn from measure- Fig. 6. Transverse section across a largo stone, which had lain on a grass-field for 35 y ars. A A, general level of the fi eld. The unclerlying brick rubbish has not been represe11ted. Scale ~ inch to one foot. ments made after it had been displaced, 1~ lwre given on a scale of ! inch to a foot (Fig. 6). The turf-covered border which sloped up to tho stone, consisted of fine vegetable mould, in one part 7 incJ1es in thickness. This evidently consisted of wormcastings, several of which had been recently ejected. The whole stone had sunk in the CuAP. HI. UNDERMINED BY WORMS. 153 thirty-five years, as far as I could judge, about 1~ inch; and this must have been duo to the brick-rubbish beneath the more protuberant parts having been undermined by worms. At this rate the upper surface of the stone, if it had been left undisturbed, would have sunk to the general level of the field in 24 7 years; but before this could have occurred, some earth would have been wa.Rhed down by heavy rain from the castings on the raised border of turf over the upper surface of the stone. The second stone was larger than the one just described, viz., 67 inches in length, 39 iu breadth, and 15 in thickness. The lower surface was nearly flat, so that the worms must soon have been compelled to eject their castings beyond its circumference. The stone as a whole had sunk about 2 inches into tho ground. At this rate it would have required 262 years tor its upper surface to have sunk to the general level of the field. The upwardly sloping, turf-covered border round the stone was broader than in tho last ca e vi7J., from 14 to 16 inches; and why this' should be so, I could see no reason. In most parts ihis border was not so high as in the |