un objet digne d'occuper le geologue, et capable de lui fournir des
remarques interessantes." Although the superficial layer of
vegetable mould as a whole no doubt is of the highest antiquity,
yet in regard to its permanence, we shall hereafter see reason to
believe that its component particles are in most cases removed at
not a very slow rate, and are replaced by others due to the
disintegration of the underlying materials.

As I was led to keep in my study during many months worms in pots
filled with earth, I became interested in them, and wished to learn
how far they acted consciously, and how much mental power they
displayed. I was the more desirous to learn something on this
head, as few observations of this kind have been made, as far as I
know, on animals so low in the scale of organization and so poorly
provided with sense-organs, as are earth-worms.

In the year 1837, a short paper was read by me before the
Geological Society of London, {2} "On the Formation of Mould," in
which it was shown that small fragments of burnt marl, cinders,
&c., which had been thickly strewed over the surface of several
meadows, were found after a few years lying at the depth of some
inches beneath the turf, but still forming a layer. This apparent
sinking of superficial bodies is due, as was first suggested to me
by Mr. Wedgwood of Maer Hall in Staffordshire, to the large
quantity of fine earth continually brought up to the surface by
worms in the form of castings. These castings are sooner or later
spread out and cover up any object left on the surface. I was thus
led to conclude that all the vegetable mould over the whole country
has passed many times through, and will again pass many times
through, the intestinal canals of worms. Hence the term "animal