The results obtained from the field work indicate that the Montreal River district does not differ essentially from the Cobalt or other neighbouring districts. The surface has the same rugged monotony of the pre-Cambrian peneplain, relieved somewhat by ridges of Huronian, which stand from 300 to 550 feet above the general level. The country is well watered, and offers exceptional facilities for canoe travel. Pleistocene deposits are thin, and nearly everywhere the rock formations are well exposed. A basement complex underlies the entire region, either appearing at the surface or hidden beneath areas of Huronian sediments. This basement consists largely of Laurentian biotite and hornblende gneisses, with patches of vertically foliated, Keewatin schists caught up in the former; the intervening contacts forming indefinite zones, in which intrusive action is manifested. In this report, for convenience, this complex will be referred to as the Archæan. The Archæan possessed a peneplanated surface, not greatly different from the present one, which is well preserved where overlain by erosion remnants of Huronian sedimentary rocks, but which at other points has been further denuded. The Lower Huronian rocks are of clastic nature, consisting in ascending order, of conglomerate, greywacke, slate and quartzite, which pass conformably into an upper conglomerate; while a granite-like, arkose member is believed from its similarity to rocks of the same character in the Cobalt area, to be possibly of later, Middle Huronian age. They are remarkably well preserved, and show only slight indication of disturbance. A later intrusion of quartz diabase has developed a system of dikes in the Archæan and large tongue-shaped areas in the Huronian believed to represent sills of several hundred feet thickness, lying in the bedding planes of the Huronian sediments. The diabase magma has been notably differentiated, giving rise to forms ranging from gabbroid to syenitic in composition, and to younger aplite dikes. With the diabase is associated a group of veins containing an association of cobalt and silver ore identical with that of Cobalt and vicinity. The veins cut both diabase and aplite as well as the Huronian, and are therefore younger, but probably not much younger than the aplite, since it contains some of the minerals found in them. The distribution of the veins so far as known is confined to the larger diabase areas, the dikes and smaller bodies being undifferentiated and unmineralized; but the Huronian adjacent to the diabase also contains veins, somewhat more siliceous, yet evidently of the same age as the others. Alteration and impregnation of the country rock has taken place to an unknown, but, presumably, limited extent. Some of the veins are remarkably rich, and many of them occupy persistent, well defined fissures. The cause of these fissures is not yet known, but they appear to be too large and continuous to have resulted from contraction alone.