GNEISSIC FOLIATION. 



117 



unreliable nature of the propositions assumed to be true. These pi'o- 

 positions are : 



(1) That gneissic foliation is a proof of bedding. 



(2) That cleavage or schistose sti-ucture is peculiarly developed in 

 sedimentary rocks. 



I shall endeavour to show by an array of instances to the con- 

 trary (1) that gneissic foliation is no pi'oof of bedding; and (2) that both 

 gneissic foliation and schistose cleavage may be developed in true 

 igneous rocks. The instances referred to are taken from the Lake 

 of the Woods region, where I have liad some opportunity of study- 

 ing the archean rocks in their various aspects. 



On an island in Sabascosing Bay, Lake of the Woods, a band of 

 black hornblende schist runs through the gneiss. The lamination of 

 the schist, the foliation of the gneiss and the line of contact are 

 coincident in direction, striking 150°, and the common dip is to the 

 north-east. The line of junction is crossed by one branch of a forked 

 dyke half a foot wide, as represented in the accompanying diagram 

 (Fig. 1):- 



Fia. 1. 



Laminated gneissoid dyke cutting' gneiss and hornblende schist. Island in Sabascosing 

 Ba.v, Lalve of the Woods. 



1. Coarse textured gray gneiss. 



2. Black hornblende schist. 



These two rocks are in conformable contact with a common strike of 150° and dip to 

 north-east. 



3. Dyke about i ft. in width, faulted at F, granitic in composition, but presenting a well- 

 marked gneissic lamination in structure. 



4. Fault cutting schists .and dyke. 



A small fault crosses the schist and has caused a dislocation, the 

 extent of which is seen by the movement of the dyke along the line 

 of fracture. The dyke is granitic in its composition, containing 

 feldspar, quartz and mica, and has a well-marked gneissic foliation of 

 the crystals parallel to the containing walls of the dyke. 



