In a communication made to the Society last session, the author stated the results of a series of explorations among the trap-rocks of Scotland, and showed that, at successive periods, during the deposition of the Lower Silurian, Old Red Sandstone, Carboniferous, Oolitic, and Tertiary formations, there were contemporaneous eruptions of volcanic material. During the year 1860, the investigation was continued across the Highlands into the Inner Hebrides, and throughout a large part of the central counties southward to the Cheviot Hills. The author was now able to fill in more fully what had only been sketched in outline in the previous paper, and to prepare a series of maps to illustrate the volcanic areas of Scotland during the successive geological periods.