Since many of the minerals grouped as hydrocarbon compounds in Dana's Mineralogy have become extensively exploited for their commercial uses, allied questions in chemical geology and in their classification have bulked largely in scientific discussion. Thus their place as rocks or minerals in petrology has been mooted; for it is difficult to make out definite chemical composition or crystallographic form in many of the materials of the group now used for heating, lighting or paving. Notably the question, What is coal ? has not been authoritatively removed from the range of scientific controversy―though the supply of the mineral which occasioned the great trial Gillespie v. Russel, nearly thirty years ago, was, until last year, considered exhausted. Diligently bored for to its exact position inthe Scottish carboniferous series of rocks, no trace of it has been found except in its limited basin of four miles area or so around Torbanehill, Linlithgowshire.