I. Introduction. The district of which the geology is here described lies north and west of the Burgh of Huntly in Western Aberdeenshire. The general form of the area and its boundaries can be seen in the accompanying map (Pl. XL), which, with a few exceptions, includes all the localities mentioned in the following pages. Allrick Hill and the Glen Burn lie west of Clashmach Hill; the Hill of Milleath and ‘Torryhillock’ lie west of Broadland and Drumdelgie; Midplough lies north-east of Rothiemay Station and east of the Deveron. With the superficial deposits this paper is scarcely concerned. The depression situated east of the high ground of Mungo, Hill of Kinnoir, and Battlehill, occupies the site of a former lake, and the thick deposit of clay hides the junctions along the hollow. Round Huntly many pits have been opened in the river-gravels deposited by the Bogie and the Deveron. Boulder Clay and glacially-striated rock-surfaces occur sparingly. Save in the north, where the igneous rocks are continued, the area in question is hemmed in by crystalline rocks, part of the ‘Banffshire Series’ of Mr. Hinxman—consisting of quartzite, limestone, phyllite, and andalusite-mica-schist. These are well developed on the west of the area, while on the east occur phyllites, grits, and conglomerates. On the east, the strike of foliation of these rocks varies, from north and south in the north, to north 60° east in the south. The dip of the foliation is vertical, or inclined to the east at a high angle.