GNEISSIC FOLIATION. 



121 



It is a coarsely crystalline gray gneiss. A little to the soiith is a nar- 

 row band of gneiss striking with the schists, of which it would be 

 difficult to say whether it was a dyke or an interbedded stratum. 

 Its origin is probably the same as that of the larger and more dis- 

 tinctly intrusive mass to the north of it. The aspect of the rock sur- 

 face on the point in question is shewn in the annexed Fig. 6. 



At the extremity of Spear Point, on the route between Rat Port- 

 age and French Portage, the mica schists, which constitute the rock 

 of the point, are cut by an irregular dyke of a porphyritic dioritic 

 rock, striking N. 60° E., with the schists as 

 shown in Fig. 7. 



The dyke has a very ragged edge and its 

 intrusive character is undoubted. It varies 

 in width from two feet to a very few inches. 

 The dyke weathers a yellowish white, and 

 presents a surface finely pimpled with thickly 

 disseminated crystals of feldspar, which have 

 been more resisting than the matrix of the 

 rock to weathering agencies. These crystals 

 show a distinctly foliated arrangement, and 

 give the rock the aspect, though it has not 

 the composition, of gneiss. The foliation is parallel with the general 

 strike of the dyke, and in addition to its gneissic structure is quite 

 schistose. 



The mica schists which occupy the north end of Hurricane Island 



Fig. 



are cut obliquely by a ragged-edged dyke of 

 whitish yellow weathering dioritic rock, which 

 is distinctly schistose. The mica schists have 

 a strike of N. 60° E., wliile the dyke and its 

 planes of schistose fracture strike about N. 40°E. 

 The following Fig. 8 shows the relation of the 

 dyke to the schists on the ground plan. 



On the west shore of Sabascosing Bay the 

 gneiss at one point is cut by a band of horn- 

 blende schist, of which neither the dyke-like 

 character nor the schistose structure can be 

 doubted. It is from one and one-half to two 

 feet wide, and strikes N. 50° W. across the gneiss, the direction of 

 whose foliation is N". 75° E. The dyke lies, as is shown in Fig. 9, 



..Ou 



