low.] GEOLOGICAL OBSERVATIONS. 25 D 



The next exposure occurs on the river at the end of the ten-mile 

 portage, and consists of buff and red gneisses. These buff rocks are a 

 decomposition-product of the red, the feldspar being dissolved out, 

 leaving a friable sandstone, consisting of quartz and magnetic grains, 

 these being probably the source of the beds of iron-sands found along 

 the river and coast. 



Similar exposure- were seen at intervals along the shores of Lake 

 Natuakimin. 



Three miles up the river beyond this lake, and fifty-eight miles from 

 the first fall, occurs an outcrop of pink crystalline limestone, coarsely 

 granular in structure, and containing crystals of mica and sphene. 



A short distance beyond is a dark grey stratified dioritic rock, com- 

 posed chiefly of quartz hornblende and triclinic feldspar, and just 

 beyond pink crystalline limestone again occurs, and here holds crystals 

 of a bluish-grey plageoclase. 



No exposures now occur on the river for thirteen miles, to where the 

 stream turns eastward and breaks through the Labradorite hills for 

 six miles to Lake Pipmuakin. The first rock here seen was a bluish- Lai 

 grey massive plageoclase feldspar, containing large crystals of the 

 same mineral. This is followed by a dark bluish-black feldspar rock. 

 with hornblende. Half a mile beyond, a gneiss, made up of plageo- 

 clase quartz and mica, occurs, and is followed by coarse-grained dark 

 plageoclase rock, weathering grey, and containing grains of magnetic 

 iron ore. 



One mile from Lake Pipmuakin was seen a dark grey triclinic feld- 

 spar rock, weathering to a light yellow. Dip S. 70° E. <70°. At this 

 point a conspicuous fault occurs on the south side of the river; the 

 hill is broken through its centre, and the east side has subsided fully 

 thirty feet. 



The above rocks are probably part of the area of plageoclase rock 

 traced by Mr. P. Adams to the north and east of Lake St. John. They 

 continue about three miles along the north-west shore of Lake Pip- 

 muakin, where they give place to a coarse-gi-ained red gneiss, and just 

 beyond a dark grey orthoclase gneiss. The contact between the 

 plageoclase rocks and the orthoclase gneisses was not seen, being 

 covered with drift. 



One mile beyond the last exposure is a light grey quartzite, contain- 

 ing considerable quantities of black mica, with a strike of N. 10° W. 

 This is followed in two miles by dark grey fine-grained gneiss, com- 

 posed chiefly of quartz and black hornblende, with orthoclase. Dip 

 X. 40° E. <7"> \ At the entrance of the north-west bay was seen red 

 and grey gneiss, changing in colour with the different proportions of 

 quartz, hornblende and orthoclase. Similar exposures occur on the 

 small islands in the bay and at the mouth of the Pipmuakin River. 



