In the second and third numbers of the ninth volume of Tschermdk's Mineralogische und petrographische Mittheilungen, I published the results of an examination of some “dolerites” from the Carboniferous basin of the Firth of Forth, the material for which I obtained through the kindness of Prof. Archibald Geikie. It is true most of the “dolerites” are already well known through the valuable writings of Professor A. Geikie and Mr Allport, but a special study of the modifications of the rock in the different parts of any one volcanic mass has not yet been the subject of any paper. Having elicited many facts of petrological interest, I purpose giving in this communication a short account of my investigations.