of .22 inches per year. Beneath the line of chalk nodules
there was in parts hardly any fine earth free of flints, while in
other parts there was a layer 21/4 inches in thickness. In this latter
case the mould was altogether 91/4 inches thick; and in one such spot a
nodule of chalk and a smooth flint pebble, both of which must have
been left at some former time on the surface, were found at this
depth. At from 11 to 12 inches beneath the surface, the undisturbed
reddish clay, full of flints, extended. The appearance of the above
nodules of chalk surprised me much at first, as they closely resembled
water-worn pebbles, whereas the freshly-broken fragments had been
angular. But on examining the nodules with a lens, they no longer
appeared water-worn, for their surfaces were pitted through unequal
corrosion, and minute, sharp points, formed of broken fossil shells,
projected from them. It was evident that the corners of the original
fragments of chalk had been wholly dissolved, from presenting a large
surface to the carbonic acid dissolved in the rain-water and to that
generated in soil containing vegetable matter, as well as the
humus-acids. The projecting corners would also, relatively to the
other parts, have been embraced by a larger number of living rootlets;
and these have the power of even attacking marble, as Sachs has shown.
Thus, in the course of twenty-nine years, buried angular fragments of
chalk had been converted into well-rounded nodules.

Another part of this same field was mossy, and as it was thought that
sifted coal-cinders would improve the pasture, a thick layer was
spread over this part either in 1842 or 1843, and another layer some
years afterwards. In 1871 a trench was here dug, and many cinders lay
in a line at a depth of 7 inches beneath the surface, with another
line at a depth of 51/2 inches parallel to the one beneath. In another
part of this field, which had formerly existed as a separate one, and
which it was believed had been pasture-land for more than a century,
trenches were dug to see how thick the vegetable mould was. By chance
the first trench was made at a spot where at some former period,
certainly more than forty years before, a large hole had been filled
up with coarse, red clay, flints, fragments of chalk, and gravel; and
here the fine vegetable mould was only from 4 1/8 to 4 3/8 inches in
thickness. In another and undisturbed place, the mould varied much in
thickness, namely, fro