On a felsite sill near Aberdeen

Abstract

Larger igneous masses are generally accompanied by minor intrusions in the form of dykes, sills, and sometimes laccoliths. Attention has recently been drawn, in some detail, to numbers of these in recent geological literature dealing with Scotch areas, as in the Survey Memoirs on the Blair Atholl and the Mid-Argyll districts. A characteristic intrusion of this nature which has never been described occurs near Aberdeen, and seems worthy of a brief notice. It crops out on the coast about two miles south of Aberdeen, and is beautifully exposed by the denudation of the coast-line. Although it does not appear on the Survey map (1 in. 77), it forms a continuous wall-like section which can be traced round the cliffs for a distance of about 700 yards. The rock forms a typical sill. It is intruded amongst banded Gneisses, which have a general dark grey aspect, and, as the sill itself is a bright red rock, the contrast is sharp and striking, and produces, indeed, a picturesque bit of coast scenery. As one follows the sill round, it is found, at the southern end of the exposure, to be quite thin, only a foot or two in breadth, and obscured by surface soil and grass. Thence it widens out, and passes, northwards, round a promontory, up the south side of a short gully, enters a cave, and emerges on the north side of the same gully as a fine long vertical wall. Then it rounds another promontory, and runs along both