In a paper by Messrs. J. R. Kilroe and A. M'Henry, M.R.I.A., which appeared in vol. lvii of the Q.J.G.S., published last August. the following statement concerning the above rock is made: “In parts they [the rock masses] consist of brecciated slate or brecciated granite and felsite, the fragments being embedded in a scanty andesitic matrix.” Now this description is quite erroneous, the great and almost unique characteristic of the Forkill agglomerate being that the greater portion is made up of non-volcanic materials—in some places of granite pieces for the most part, in a groundmass of finely comminuted material of the same rock, and in others of Silurian slate fragments in a correspondingly derivative base. This I have described long ago in the official memoir to accompany Sheet 70 of the Geological Survey Map of Ireland, as also in the following papers: “On a Remarkable Volcanic Agglomerate near Dundalk” (J.R.G.S., Ireland, new series, vol. iv, pt. 4) and “On the Ancient Volcanic District of Slieve Gallion” (Geol. Mag., Dec. II, Vol. V, October, 1878).