On the Norian or "Upper Zaarentian" Formation. 303 



40° to 80° W., and on the upper part of the Peribonka, 

 K 10° to 20° W. The fact that the strike of the gneiss 

 and that of the anorthosite near the limit of the area 

 coincide, notwithstanding that it is crossed several times 

 by the line of contact, can easily be explained as caused 

 on the east and the west side by a series of cross faults, 

 if it be assumed that the foliation of the anorthosite here 

 originally coincided with the direction of the boundary. 

 It is almost certain that such faults exist. The condition 

 of things, however, at the southern boundary where the 

 contact may be more accurately investigated, but where, 

 unfortunately, the foliation of the anorthosite and of the 

 gneiss is mostly very indistinct, rather points to the fact 

 that this conformity is the result of a pressure, which was 

 exerted upon the anorthosite in a direction almost at 

 right angles to the ordinary strike of the gneiss. The 

 greater predominance of the granulation on the east side 

 of the area suggests that the pressure came from that 

 direction. The less definite indications of foliation or 

 streaked structure which were observed here and there in 

 the usually massive anorthosite of the interior of the 

 area, and which do not coincide in direction with that of 

 the gneiss and anorthosite about the edge of the area, 

 probably belong to the original structure, due to move- 

 ments in the magma before con- 

 solidation. This view is supported 

 by a series of larger exposures of 

 anorthosite at the east end of Lake 

 Tschitogama. The rock there is 

 distinctly striped, bands of plagio- 

 clase almost free from bisilicates 

 alternating with others in which 

 the latter are quite abundant. The 

 Fig 8 bisilicates are disposed in elongated 



masses or in short dashes which are parallel to one 

 another, but have a different direction from that of the 



