1854.] BIGSBY GEOLOGY OF RAINY LAKE. 217 



constituents. In patches we find it of a pale salmon tint, from the 

 colour of its felspar. In the northern parts of this shore it is finely- 

 granular and porphyritic, in equal quantities. At the River Nahcat- 

 chewonan, the granite cannot be distinguished from that of Gravel 

 Point and other districts in the Lake of the Woods, about forty 

 miles distant on the W.N.W. The northern half of this western 

 shore is for the most part a perfectly naked, bleached rock. 



In Peche and Otter Bays, and for five or six miles northwardly, by 

 the admission of hornblende and other changes in its constitution, the 

 granite becomes a syenite, which, in its turn, by patches, becomes a 

 hornblende-greenstone, and even slaty ; while over the whole western 

 shore, in places too numerous to designate, but occasionally noted on 

 the Map, it passes into gneiss. Whether this is eifected here by 

 gradual transition, I cannot say, but intercalations of these two 

 rocks are frequent ; and so is the occurrence of veins of porphyritic 

 granite, traversing the gneiss in all directions without disturbance of 

 any kind (two miles N.E. of Cape Jones, &c.). 



Throughout this coast, round and lenticular masses of black horn- 

 blende occur, both in the granite and in the gneiss, from 100 to 300 

 yards in length, and often ramifying far and near into the containing 

 rock ; — or it may be interleaved with the gneiss, as in Nahcatche- 

 wonan Bay, four miles west of Cape Jones. Point Otter is a headland 

 of this rock, 250 yards broad. It is penetrated from below by 

 granite, whose main seams (4-6 yards broad) rise up perpendicularly, 

 but which ramify and inosculate very freely in the smaller branches. 



On the north side of Nahcatchewonan Bay, this black hornblende 

 is very abundant; and near Cape Jones a mass of it occurs in layers, 

 which open and contain a large lenticular lump of crystalline quartz. 

 It also abounds on the east side of Manitou Sound for ten miles 

 south of Corpse Island, and here it passes conformably into a dark 

 gneiss. 



The strikes and dips of the gneiss are so various as only to be 

 understood from the Map, where it will be further seen that the 

 form and direction of the Western Arm (twenty-five miles long) and its 

 different bays and inlets are greatly governed by the stratification ; 

 a remark which must be extended to the whole of Rainy Lake. 



Second Division. — The second portion, with its winding shores, 

 commences at Cape Chamberlin. Here a total change of rock takes 

 place ; but under what circumstances, the marshy nature of the 

 countrj^ prevents us from seeing. 



This whole line of coast (thirty-six miles) is based on greenstone-slate 

 and chlorite-slate, passing into each other insensibly. Although of 

 several shades of green elsewhere, and very fissile, the greenstone of 

 Hopkins and Indian Bays is black, very compact, and often in such 

 broad strata (many yards across) as to be ali-«ost massive. In this 

 state it changes into syenite, in and near the two bays just men- 

 tioned, in spaces of a few square miles, and is either interleaved 

 with the two slates in broad seams, or is in intrusive masses, con- 

 taining numerous and large imbedded lumps of nearly pure horn- 

 blende. 



