Associated with them and to the northward, are dikes of light coloured, granite porphyry, usually only a few feet wide, in some of which the original massive structure remains, while others show various gradations toward a felsitic, sericite-bearing schist. The isolated patch of Keewatin indicated on the map as occurring about half a mile east of the wide portion of Duncan lake, is a well foliated green schist in which oval white spots represent squeezed feldspar phenocrysts. [Illustration: Fig. 4. View looking north from middle of Duncan Lake, 550ʹ hill in distance.] _Pigeon Lake Area._ West of Pigeon lake and the Montreal river, much of the country examined is underlain by Keewatin. Schistosity is less developed than in either of the preceding areas. The rocks are chiefly diabases and porphyry much decomposed and locally squeezed. Diabase occurs on both sides of Pigeon lake near its central islanded part and along the bay which extends south to Brush lake. An original diabase structure is sufficiently well preserved to show lath-like feldspars in hand specimens, but frequently the rock is altered to a chloritic mass. Around the bay extending toward Brush lake, this old diabase forms a rude wall intersected by a reticulating system of fractures filled with calcite, the resultant structure simulating that of a breccia. Shear zones seen on the east shore exhibit a pseudo-conglomeratic structure, the more resistant pieces of diabase having been partially rounded by the shearing movement and embedded in a matrix of finely pulverized rock matter. The same diabase apparently occurs all along the Montreal river where it follows the Algoma-Nipissing line. About half a mile above Pigeon lake it forms a 90 foot cliff on the west side of the river, near the top of which is a fresher looking, unfoliated eruptive. The form of this body was not ascertained, but microscopic examination of the specimen taken, determines it to be a hornblende lamprophyre, so probably it is a dike or thin sheet. The rock is fine-grained, dark green in colour and characterized by stout prisms of hornblende about one-quarter of an inch long, embedded in a finer, microcrystalline ground mass. Under the microscope it appears much decomposed. This rock was also observed near mile post 67 of the Algoma-Nipissing boundary, near the east end of the 63 chain portage leading to Breese lake and at other points, in all cases the exposures being of small extent. In the last mentioned locality the predominant rock is an altered porphyry of ash grey colour. Around Porphyry lake it occurs in a fairly massive, easily recognizable condition, the feldspars showing as square white spots one-quarter of an inch in diameter in a grey, ground mass. On Breese lake it has been squeezed to a felsite schist, striking N. 20° W. In small amounts it is associated with post-Huronian diabase on the hills lying near the Montreal river and just south of the 63 chain portage.