r ages, the minute
seed-spores of forest trees were in such abundance as to form important
seams of coal in the true carboniferous era, the trees which gave birth
to them being now classed amongst the humble _cryptogams_, the ferns, and
club-mosses, &c. The graphite of Laurentian age may not improbably have
been caused by deposits of minute portions of similar lowly specimens of
vegetable life, and if the _eozooen_ the "dawn-animalcule," does represent
the animal life of the time, life whose types were too minute to leave
undoubted traces of their existence, both animal life and vegetable life
may be looked upon as existing side by side in extremely humble forms,
neither as yet having taken an undoubted step forward in advance of the
other in respect to complexity of organism.

[Illustration: FIG 30.--_Lepidodendron_. Portion of Sandstone stem after
removal of bark of a giant club-moss]

There is but one more form of carbon with which we have to deal in
running through the series. We have seen that coal is not the _summum
bonum_ of the series. Other transformations take place after the stage of
coal is reached, which, by the continued disentanglement of gases,
finally bring about the plumbago stage.

What the action is which transforms plumbago or some other form of carbon
into the condition of a diamond cannot be stated. Diamond is the purest
form of carbon found in nature. It is a beautiful object, alike from the
results of its powers of refraction, as also from the form into which its
carbon has been crystallised. How Nature, in her wonderful laboratory,
has precipitated the diamond, with its wonderful powers of spectrum
analysis, we cannot say with certainty. Certain chemists have, at a great
expense, produced crystals which, in every respect, stand the tests of
true diamonds; but the process of their production at a great expense has
in no way diminished the value of the natural product.

The process by which artificial diamonds have been produced is so
interesting, and the subject may prove to be of so great importance, that
a few remarks upon the process may not be unacceptable.

The experiments of the great French chemist, Dumas, and others,
satisfactorily proved the fact, which has ever since been considered
thoroughly established, that the diamond is nothing but carbon
crystallised in nearly a pure state, and many chemists have since been
engaged in the hitherto futile endeavour to turn ordinary carbon int