Dr Fleming, after stating the circumstances which led him to bring before the Royal Society the consideration of this question, pointed out the distinction between a mineral species and a rock, a circumstance which had been greatly overlooked in recent discussions on the subject. He considered coal as a rock, and capable of being traced, in its origin and history, from peat at the beginning of the series, to blind coal or anthracite at the termination.

He illustrated the character of peat in reference to the vegetables from which it was derived—the changes of a mineralizing nature which it had undergone—and the strata of sand, clay, and marl with which it is usually associated.