第30章

Two recently published accounts of substances strewed on the surface of pasture-land, having become buried through the action of worms, maybe here noticed.The Rev.H.C.Key had a ditch cut in a field, over which coal-ashes had been spread, as it was believed, eighteen years before; and on the clean-cut perpendicular sides of the ditch, at a depth of at least seven inches, there could be seen, for a length of 60 yards, "a distinct, very even, narrow line of coal-ashes, mixed with small coal, perfectly parallel with the top-sward." This parallelism and the length of the section give interest to the case.Secondly, Mr.Dancer states that crushed bones had been thickly strewed over a field; and "some years afterwards" these were found "several inches below the surface, at a uniform depth."The Rev.Mr.Zincke informs me that he has lately had an orchard dug to the unusual depth of 4 feet.The upper 18 inches consisted of dark- coloured vegetable mould, and the next 18 inches of sandy loam, containing in the lower part many rolled pieces of sandstone, with some bits of brick and tile, probably of Roman origin, as remains of this period have been found close by.The sandy loam rested on an indurated ferruginous pan of yellow clay, on the surface of which two perfect celts were found.If, as seems probable, the celts were originally left on the surface of the land, they have since been covered up with earth 3 feet in thickness, all of which has probably passed through the bodies of worms, excepting the stones which may have been scattered on the surface at different times, together with manure or by other means.It is difficult otherwise to understand the source of the 18 inches of sandy loam, which differed from the overlying dark vegetable mould, after both had been burnt, only in being of a brighter red colour, and in not being quite so fine- grained.But on this view we must suppose that the carbon in vegetable mould, when it lies at some little depth beneath the surface and does not continually receive decaying vegetable matter from above, loses its dark colour in the course of centuries; but whether this is probable I do not know.

Worms appear to act in the same manner in New Zealand as in Europe; for Professor J.von Haast has described a section near the coast, consisting of mica-schist, "covered by 5 or 6 feet of loess, above which about 12 inches of vegetable soil had accumulated." Between the loess and the mould there was a layer from 3 to 6 inches in thickness, consisting of"cores, implements, flakes, and chips, all manufactured from hard basaltic rock." It is therefore probable that the aborigines, at some former period, had left these objects on the surface, and that they had afterwards been slowly covered up by the castings of worms.

Farmers in England are well aware that objects of all kinds, left on the surface of pasture-land, after a time disappear, or, as they say, work themselves downwards.How powdered lime, cinders, and heavy stones, can work down, and at the same rate, through the matted roots of a grass- covered surface, is a question which has probably never occurred to them.

The Sinking of great Stones through the Action of Worms.--When a stone of large size and of irregular shape is left on the surface of the ground, it rests, of course, on the more protuberant parts; but worms soon fill up with their castings all the hollow spaces on the lower side; for, as Hensen remarks, they like the shelter of stones.As soon as the hollows are filled up, the worms eject the earth which they have swallowed beyond the circumference of the stones; and thus the surface of the ground is raised all round the stone.As the burrows excavated directly beneath the stone after a time collapse, the stone sinks a little. Hence it is, that boulders which at some ancient period have rolled down from a rocky mountain or cliff on to a meadow at its base, are always somewhat imbedded in the soil; and, when removed, leave an exact impression of their lower surfaces in the underlying fine mould.If, however, a boulder is of such huge dimensions, that the earth beneath is kept dry, such earth will not be inhabited by worms, and the boulder will not sink into the ground.