12 



same transition occurs in reverse order, the western margin 

 consisting of dark red syenites like those near Peninsula. 

 A great variety of rock types, ranging from nepheline 

 syenite to olivine gabbro, is present but they are all 

 evidently the result of one act of plutonic intrusion. 

 The latest investigators regard the order of consolidation 

 to have been in general from the most basic to the most 

 acid type, followed by a final intrusion of dykes of camp- 

 tonite and allied materials. 



The mass is intrusive into Keewatin schists and Lau- 

 rentian granite-gneiss. 



Lake Superior is in sight at intervals from Peninsula to 

 Nipigon 



The Keewatin and Laurentian rocks that reappear at 

 Middleton continue to Gurney where they become over- 

 lain by flat-lying Keweenawan sediments and diabase 

 sills intrusive into these sediments. The first of these 

 formations seen is a bright red sandy dolomite, which con- 

 tains disseminated patches of gypsum, and other evidences 

 of arid climatic conditions at the time of its deposition. 



The intrusive diabase sills appear near Kama, giving 

 a first impression of the precipitous mesa-like topography 

 which they produce in greatest prefection near Fort 

 William. The shore deposits of old Lake Algonquin are 

 also exposed in cuttings near Nipigon. 



Between Nipigon and Port Arthur, Animikie (Upper 

 Huronian) and Lower Huronian rocks also appear. These 

 as well as the other Pre-Cambrian series are particularly 

 well exposed near Loon. In this locality which is described 

 more fully in the guide-book of Excursion Ci, the Keewatin 

 volcanic rocks and Lower Huronian conglomerate, grey- 

 wacke and greenstone have been intruded by Laurentian 

 granitic batholiths and so folded and altered to schists that 

 a separation of the two groups is almost impossible. The 

 flat-lying and little metamorphosed Animikie sediments 

 lie unconformably upon a greatly eroded surface of these 

 older rocks. They consist, from top to bottom, of (i) 

 black slate, (2) upper iron formation, (3) slate, (4) 

 thin-bedded, impure limestone, (5) iron formation, and (6) 

 quartz conglomerate. The lower iron formation, is, 

 perhaps, of greatest interest for it exhibits a variety of 

 stages in the development of iron ore from the lean iron 

 formation. Keweenawan conglomerate, sandstone and 

 impure limestone, all deposited in shallow water, lie un- 



