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The Laurentian granites and gneisses are intrusive in the Ontarian, and are therefore younger, the relations between the two being the same as described by Lawson in the Rainy Lake district.

Resting discordantly upon the Laurentian and Ontarian rocks, is the Steep Rock series, presumably of Archean age. This series is believed to be a folded syncline, rather than a monocline, as described by Smyth. As the Animikie series exhibits no such folding, the inference is strong that the Steep Rock series is older than the Animikie. While the unconformity between the Steep Rock series and Laurentian is undoubted, the unconformity between the Keewatin of the Seine river and the Steep Rock Lake series is not at all obvious. Lithologically the two series are strikingly similar, and could not be separated by the most careful study. It would seem that to the west of Steep Rock Lake this series has been faulted up and swept away, so that it is really unconformably above the Keewatin. The Atic Oban series is an eruptive one probably belonging to the Keewatin.

Comments.—Since the Steep Rock Lake series is almost identical in character with the Keewatin, the assumption of profound faulting and erosion to explain the absence of the former series west of Steep Rock Lake seems purely gratuitous, the natural explanation being that the two are the same, and that the discordance at the base of the Steep Rock series is marked in other localities by the occasional conglomerates described by Lawson and Smith at the base of the Keewatin. The unconformities are partly obliterated or difficult to discover when the discordant series are closely folded is well known, and that a break, if such exists at the base of the Keewatin, should be so strongly marked everywhere as at Steep Rock Lake could not be expected. A conglomerate in itself is of course no evidence of unconformity, but the conglomerates at the base of the Keewatin are of such a character that Dr. Lawson, who has studied the district, believes that they mark, if not a real unconformity, a profound change of physical conditions between the Contchiching and Keewatin. Also he holds that these conglomerates are sedimentary, rather than volcanic.

Fine and even lamination, it may be said, is not sufficient evidence that the rocks showing this structure are clastic. Such structures are found both in metamorphosed igneous and sedimentary rocks. Moreover, it cannot be assumed that such a structure corresponds with bedding, even if the rocks are clastic. Hence, until it is shown that the two do correspond, determinations of thickness based upon lamination can have little value.

Buell^[1] describes and maps the Waterloo quartzite areas. These are a series of detached outcrops resting unconformably under the Lower Silurian