5i 



which they are imbedded are absolutely free from all signs 

 of pressure. 



The banding and foliation of the nepheline syenite 

 gradually passes over into the bedding and foliation of the 

 limestones. Abundant development of black mica in the 

 limestone at the immediate contact with the nepheline 

 syenite is seen here as in many other places in the district 

 where the contact of these two rocks can be examined. 

 Thin beds of limestone and associated paragneisses and 

 amphibolites included in the syenite are sometimes so 

 filled with the minerals characteristic of the syenite that 

 it is almost impossible in the field to determine whether 

 they belong to the limestone series or to the invading 

 magma. North from Bancroft on the Hastings road, 

 exposures of nepheline syenite with some included bands of 

 limestone are seen on the east side of the road. 



One mile from the village the gneissic granite of the 

 great northern batholith is reached, forming a great cliff 

 known as the "Eagle's Nest". The granite-gneiss here 

 is reddish and possesses a distinct foliation, striking almost 

 at right angles to the road and dipping south, thus dis- 

 appearing beneath the nepheline syenite border complex, 

 which in its turn is overlaid by limestone. This gneissic 

 granite is of medium grain with occasional coarsely crys- 

 talline segregations. Under the microscope it is seen to 

 be composed of orthoclase, microcline, albite and quartz. 

 Only a very small quantity of biotite is present. A 

 ferriferous variety of sphene, magnetite and occasional 

 small crystals of ziron complete the list of constituents. 

 The rock shows marked evidence of pressure. This is 

 especially seen in the quartz, which always displays 

 strain shadows and is frequently granulated along certain 

 lines. 



It is a typical representative of the granite gneiss of 

 the northern batholith of this area ("Fundamental Gneiss") 

 except that here it is practically free from the dark amphi- 

 bolite inclusions which are such a characteristic feature 

 ^f the gneiss in almost every other part of the region. 



About three miles (4-8 km.) north-east of Bancroft, 

 the nepheline syenite is in certain places very rich in soda- 

 lite, this mineral being especially abundant in very coarse- 

 grained pegmatite segregations which usually occur inter- 

 banded with the normal type of nepheline syenite. The 

 colour of the sodalite varies from a very dark cobalt blue 



35064— 4I 



