I. INTRODUCTION. The object of this paper is : First, to describe the Moine Gneisses in:Perthshire and Aberdeenshire, and to show that in their mode of occurrence and field-characters, as well as in their composition and microscopic structures, they are identical with the Moine Gneisses of the North-Western Highlands. Secondly, to trace the mode of ending-off of these gneisses, and to show that, while retaining their characteristic parallel banding they pass into a small zone of rocks, locally known as the Hon estones, which, in varying phases, lie persistently for miles oll the white margin of the Central-Highland Quartzite. The parallel-banded Moine Gneisses are, in fact, simply the flaggy margin of this Quartzite. Thirdly, to show, that in this special area, as the flaggy rocks thicken, there is usually a small hiatus in the succession, owing either to the contemporaneous erosion of the finer material that should lie next them, or to its non-deposition. When this parallelbanded material, however, attains a certain degree of fineness, this erosion rarely occurs, and then the other limit of the group is the Little Limestone. In fact, when the succession is complete, the Moine Gneisses can be shown to pass laterally into the rocks ofthe Honestone Group, and to lie between the white margin of the Quartzite and the Little Limestone. Whether these flaggy rocks lie above or below the Quartzite is at present a matter of dispute. The view here taken is that they come above the Quartzite, and the evidence for that view