gather together all that goes up the chimney; and all that remains in
the grate of a thoroughly-burnt coal-fire, we should find ourselves in
possession of a quantity of carbonic acid, water, ammonia, and mineral
matters, exactly equal in weight to the coal. But these are the very
matters with which Nature supplied the club-mosses which made the
coal. She is paid back principal and interest at the same time; and
she straightway invests the carbonic acid, the water, and the ammonia
in new forms of life, feeding with them the plants that now live.
Thrifty Nature! Surely no prodigal, but most notable of housekeepers!




VI.

ON CORAL AND CORAL REEFS.


The marine productions which are commonly known by the names of
"Corals" and "Corallines," were thought by the ancients to be
sea-weeds, which had the singular property of becoming hard and
solid, when they were fished up from their native depths and came into
contact with the air.

"Sic et curalium, quo primum contigit auras Tempore durescit:
mollis fuit herba sub undis,"

says Ovid (Metam. xv.); and it was not until the seventeenth century
that Boccone was emboldened, by personal experience of the facts, to
declare that the holders of this belief were no better than "idiots,"