V. On the present distribution and orgin of the calcareous concretions in coal seams, known as "coal balls"

Abstract
To botanists and geologists alike coal and the beds associated with it afford a rich field for investigation. Geologists have long been particularly fascinated by the theories which attempt to account for the mode of origin of the coal, and as a result a vast literature has been built up in support of the various views of the authors who have dealt with the problem. Nevertheless, for our purpose, it is enough merely to name the two main theories which now hold the field, as the “growth in situ ” and the “drifted” origin for the plants which compose the coal. It will, perhaps, be well to express clearly at the beginning of this paper that we do not propose to enter into a critical discussion of the views of other writers on the subject, except where they have a very direct bearing on our own investigation. It will be found that the results of our work have a certain bearing on the wider subject of the origin of coal in general, but in this paper we wish to confine ourselves to the consideration of questions suggested by the “coal balls” in particular. The conclusions drawn from the special aspect of the case are not applicable to all seams of coal, though they illustrate fully the history of certain seams. The calcareous masses which occur actually embedded in the coal of some districts have proved of vital importance to students of botanical anatomy and phylogeny, because they contain plant tissues so perfectly petrified that the complete structure of the plants can be discovered by microscopic investigation. Yet although these calcareous masses or “coal balls” have been the source of so much valuable information, little is to be found in the literature, and one gathers also that but little is actually known to scientists about their mode of occurrence and the many interesting phenomena presented by their relation to the beds in which they are found. We have endeavoured to collect and preserve information about these structures, which are being daily destroyed, information which may prove of service to both botanists and geologists.