Practically all the Laurentian lies in a continuous area, east of the West branch and extending beyond the limits of the map sheet. A smaller body occurs just west of Pigeon lake. The foliation in the Laurentian is less distinct than in the Keewatin and much less perfect. Its component rocks are mainly granite and allied plutonic types which pass by easy gradations into well-defined gneisses. Two principal granites are distinguishable; one containing black mica as its chief coloured constituent, the other hornblende. Both exhibit local variations in composition and crystalline texture, but are always pale grey rocks of ordinary granitic appearance. The hornblende granite is a medium grained, fresh looking rock of speckled appearance, owing to the black hornblende crystals which lie scattered through the main mass of light grey feldspar and quartz. It is of uniform aspect, local variations of colour and texture being insignificant. As revealed under the microscope by a single thin section, it is an ordinary hornblende granite verging towards a syenite. Common green hornblende of idiomorphic prismatic habit, and usually twinned parallel to 100, is the principal ferromagnesian mineral. It is quite fresh, hence a few flakes of chlorite in the section were taken to represent an original small content of biotite; an acid oligoclase and orthoclase are the most abundant constituents; quartz is subordinate. Apatite, zircon and iron ore, probably magnetite, are accessory. Hornblende granite is the commonest Laurentian rock in the neighbourhood of L’Africain and Sedge lakes, where it is in contact with the Keewatin. It also occurs on the East branch just below Obushkong lake. The area west of Pigeon lake seems to be composed wholly of this rock, outliers of which extend to Brush lake, and the islands and east shore of Pigeon lake. Here, however, it is distinctly syenitic, quartz being subordinate or absent. A distinctly porphyritic structure is apparent on Pigeon lake; the feldspars being well crystallized and lying in a finer grained, holocrystalline ground mass.