1 1 6 THE JO URN A L OF GEOLOG V. 



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. 



Co77iments. — Since the Steep Rock Lake series is almost identical in char- 

 acter 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. That 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 sedi- 

 mentary, 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' describes and maps the Waterloo quartzite areas. These are a 

 series of detached outcrops resting unconformably under the Lower Silurian 



^ Geology of the Waterloo Quartzite Area. By L M. Buell. Trans. Wis. Acad. 

 Sci., Vol. IX., pp. 255-274. 



