13 



conformably upon the Animikie. These formations as 

 well as the older ones, are intruded by dykes and sills of 

 diabase. 



The relations of these sills to the Animikie sediments is 

 particularly well shown in Current River park, Port Arthur, 

 where a flood, caused by the bursting of a dam, has swept 

 the rock floor quite free of soil. This rock floor consists 

 largely of the upper surface of a diabase sill upon which 

 vestiges of the original covering of black slate still adhere. 

 Slight contact metamorphic changes are observable in the 

 slate, and there are local anorthosite segregations a few 

 feet in diameter in the diabase due to aggregation of 

 labradorite phenocrysts. 



The Port Arthur district contains a number of silver 

 mines, including the famous Silver Islet mine, which bear 

 considerable resemblance to those at Cobalt. The deposits 

 are fissure veins carrying native silver, native bismuth, 

 and various arsenides, antimonides, sulph-arsenides, etc., 

 of silver, cobalt and nickel. Like the Cobalt deposits also, 

 they are closely associated with the intrusive diabase sills. 

 The Port Arthur district is described at greater length in 

 the guide-book of Excursion Ci. 



Between Fort William and Summit, a distance of i8 

 miles (29-0 km.) the railway traverses a flat delta plain 

 but the characteristic flat-topped hills of this locality 

 appear in the distance to the south. These, of which 

 mount McKay is perhaps the best example, consist of 

 flat-lying easily eroded Animikie sediments protectively 

 capped by remnants of the intrusive diabase sills. 



These formations thin out and finally disappear near 

 Summit beyond which lies another great region of Lauren- 

 tion gneisses and Keewatin schists. This region, extending 

 for 340 miles (547 km.) to Darwin, is more heavily drift 

 covered than that along Lake Superior but is not essentially 

 different from it structurally or lithologically. The gla- 

 ciated topography is more subdued and rocky lakes 

 are more numerous. Excellent views of Eagle lake are 

 obtained at Vermilion and of Lake of the Woods just 

 west of Kenora. Gold is mined on Eagle lake. Lake of 

 the Woods and at numerous other points in the Keewatin 

 south of the railway. The stratified clay near Dryden, 

 which was probably deposited in a small glacial lake, sup- 

 ports a scattered farming community and is used for brick- 

 making at Dryden. 



