The relationships of the Laurentian to the other systems of the region are expressed by the contacts with them. Between Obushkong and Firth lakes and toward L’Africain lake it is largely in contact with Keewatin. This contact is a vaguely defined zone rather than a line, the formations being separated by the intermediate strip containing mingled portions of both. Proceeding across this strip from the Laurentian to the Keewatin, the gneisses of the former become charged with ribbons of highly crystalline schist, already described. Near the Keewatin edge these increase in quantity and sometimes appear as tongue-like protrusions of that system. This condition exists along the east of L’Africain lake; on the shores of the lake the formation is dominantly Keewatin, but the stratiform hornblende gneiss is traversed along the strike by thin bands of Laurentian hornblende gneiss. A few chains eastward the gneiss bands are wider, and, at a distance of 10 chains, hornblende granite is continuous. Where terminated by diabase the contact is definite and not marked by notable alteration on either side. Contacts with the Huronian are equally sharp and unconformable, in every case the Laurentian disappearing beneath the sedimentary formation; at the south end of Kenisheong lake the Huronian has been trenched to a depth sufficient to expose the underlying gneissic floor near the water’s edge. HURONIAN. _General Features._ Much of the area mapped, especially the north-western portion, is composed of Huronian rocks. Originally they must have been much more extensive, probably continuous, but erosion has removed them partially or entirely, leaving irregular remnants distributed over the Archæan. The top of the series is gone; consequently complete vertical sections cannot be found. In other respects they are little changed and preserve almost perfectly their bedding and clastic structure. Even their positions assumed at the time of deposition have changed little for the present strata seldom dip more steeply than 30°. They are overlain only by unconsolidated Pleistocene materials. _Basal Conglomerate._ The basal member of this system is a conglomerate, the areal exposure of which is inconsiderable for the whole region or for any part, but erosional sculpturing has brought it to light at many points. Both top and bottom and probably all intermediate portions are visible, but a complete section from which to determine the thickness could not be found. The greatest continuous vertical section observed, in a hill lying one mile south of the 550 foot hill north-west of Duncan lake, is about 200 feet, but neither upper nor lower terminations were seen. In the neighbouring Cobalt district an estimated thickness of 500 feet has been assigned.