288 



B. KOTO. 



their contact with the Laurentian rocks, leave no room for doubt bnt 

 that these inchisions are detached portions of the overlying formations, 

 which, in a firm and brittle condition, have become immersed in the 

 nnderlying viscid magma, which subsequently crystallized out as 

 the Laurentian gneiss and granite. This mode of foliation of 

 the granites (plastic deformation) seems to have been produced by 

 differential pressures upon the tliickly viscid magma, inducing a 

 flow in the mass, similar to that endogenous growth of a volcano 

 by Naclischuh, experimentally observed by Reyer. To this fl(^w is 

 ascribable both the schist(3sity of certain foKated granites, and the 

 parallel arrangement of enclosures of foreign rocks imbedded in it, as 

 in the Rainy Lake region.^ It must be expressly remarked that there 

 is another process which leads to the formation of foliation, (juite 

 distinct from that just mentioned, wlvich may be termed that of 

 s:)liil di'funiiatio)!, since the schistosity is in this case brought about by 

 internal granulation of tlie component-minerals. Foliated granites, 

 which occupy extensive area in the plateau, owe tVieir structure to the 

 latter actioij. 



The upper arcluean is represented by bedded formations, in which 

 can be recognized at least two leading groups. 



One of them is the Takanuki series which is again divisible into 

 tlie lower acid, and the upper basic member. «) The former rests 

 directly upon the Laurentian. and its petrogra|)lrical elements are 

 gneiss-mica schist, two-mica schist, garnet-biotite schist, and horn- 

 blende-biotite schist, which together make up the considerable thick- 

 ness of 5,000 metres. All these rock- varieties have in common a 

 tabular form witli the plane-parallel structure, and their transverse 

 sections show^ the interbanding of black-mi (,'a zones with light- 

 greyish quartz-feldspar layers (photograph, figure 2, -Pi. XXVII). 



1 Andrew 0. Lawson, On the Gealogy of the Rainy Lake Region, p. 131. et seq. 



