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. 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 corrosion from the action of carbonic acid in the
course of only seven years.
Much better evidence 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
swallowed 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 tesser on one of the buried floors of the Roman villa at
Abinger, there were many particles (from 1 2 to 2 mm. in diameter) of tiles
and concrete, which it was impossible to look at with the naked eye or
through a strong lens, and doubt for a moment that they had almost all
undergone much attrition. I speak thus after having examined small
water-worn pebbles, formed from Roman bricks, which M. Henri de Saussure
had the kindness to send me, and which he had extracted from sand and
gravel beds, deposited on the shores of the Lake of Geneva, at a former
period when the water stood at about two metres above its present level.
The smallest of these water-worn pebbles of brick from Geneva resembled
closely many of those extracted from the gizzards of worms, but the
larger ones were somewhat smoother.
Four castings found on the recently uncovered, tesselated floor of the
great room in the Roman villa at Brading, contained many particles of
tile or brick, of mortar, and of hard white cement; and the majority of
these appeared plainly worn. The particles of mortar, however, seemed to
have suffered more corrosion than attrition, for grains of silex often
projected from their surfaces. Castings from within the nave of Beaulieu
Abbey, which was destroyed by Henry VIII., were collected from a level
expanse of turf, overlying the buried tesselated pavement, through which
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