Many years ago, in the clay which in every part of the world is found underlying beds of coal, a peculiar fossil was discovered and named by science Stigmaria. It occurred in great abundance and in many countries, and from the strange way in which it ramified through the clay it was supposed to be some extinct variety of a gigantic water-weed. In the coal itself another fossil was discovered, almost as abundant but far more beautiful, and from the exquisite carving which ornamented its fluted stem it received the name of Sigillaria. One day a Canadian geologist, studying Sigillaria in the field, made a new discovery. Finding the trunk of a Sigillaria standing erect in a bed of coal, he traced the column downwards to the clay beneath. To his surprise he found it ended in Stigmaria. This branching fossil in the clay was no longer a water-weed. It was the root of which Sigillaria was the stem, and the clay was the soil in which the great coal-plant grew.

Through many chapters, often in the dark, everywhere hampered by the clay, we have been working among roots. Of what are they the roots? To what order do they belong? By what process have they grown? What connection have they with the realm above, or the realm beneath? Is it a Stigmaria or a Sigillaria world?