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Show 252 DISINTEGRATION CnAP. V. rubbish on both sides of the road for a width of 18 inches, and on this turf there were innumerable castings. Some of them were coloured of a uniform red owing to the presence of much brick-dust, and they contained many particles of brick and of hard mortar from 1 to 3 mm. in diameter, most of which were plainly rounded; but all these particles may have been rounded before they were protected by the turf and were swallowed, like those on the bare parts of the road which were much worn. A hole in a pasture-field had been filled up with brick-rubbish at the same time, viz., seven years ago, and was now covered with turf; and here the castings contained very many particles of brick, all more or less rounded ; and this brick-rubbish, after being shot into the hole, could not have undergone any attrition. Again, old bricks very little broken, together with fragments of mortar, were laid down to form walks, and were then covered with from 4 to 6 inches of gravel; six little fragments of brick were extracted from castings collected on these walks, three of which were plainly worn. CliAP. V. AND DENUDATION. 253 There were also very many particles of hard mortar, about half of which were well rounded; and it is not credible that these could have suffered so much corro ion from the action of carbonic acid in the course of only seven years. Much better eviJenco of the attrition of hard objects in the gizzards of worms, is afforded by the state of the small fragments of tiles or bricks, and of concrete in the castings thrown up where ancient buildings once stood. As all the mould covering a field passes every few years through the bodies of worms, the same small fragments will probably be swa1lowed and brought to the surface many times in the course of centuries. It should be premised that in the several following cases, the finer matter was first washed away from the castings, and then all the particles of bricks, tiles and concrete were collected without any selection, and were afterwards examined. Now in the castings ejected between the tesserre on one of the buried floors of the Roman villa at Abin()'er 0 ' there were many particles (from ~ to 2 mm. in diameter) of tiles and concrete, which it |