GEOLOGY OF THE LONG LAKE QUADRANGLE 469 



oiit, both above and below. It also occurs away from them in the 

 general body of the gneiss. It may be a phase of the Long lake 

 gneiss modified in appearance by the incorporation of Grenville 

 material, but this seems unhkely, in view of its composition and it 

 is tentatively regarded as a Grenville igneous rock, one whose in- 

 jection took place during, or only shortly after, the deposition of 

 that series. It is also thought that there are gabbros of similar age 

 in the region, though no such have been identified within the quad- 

 rangle limits. 



There are various other varieties of gneiss found in the Grampus 

 vicinity, though of very minor importance compared to those 

 already enumerated. The whole mass is well banded, with frequent 

 variations in composition and gives the impression of a Grenville 

 area so intruded with igneous rocks of all kinds -and ages that the 

 Grenville has well nigh disappeared, the whole subsequently exces- 

 sively metamorphosed. In consideration of its complicated nature, 

 and the trifling amount of certain sediments included, it is thought 

 wiser to give it a noncommittal mapping than to map it separately 

 from the Long lake gneiss. 



Piercefield gneiss. In the extreme northwest corner of the 

 quadrangle there appears the eastern apex of a great mass of gneiss 

 which lies mostly beyond the quadrangle limits, and which affords 

 a somewhat different rock admixture from either of the foregoing. 

 The rocks are excellently exposed about Piercefield, and in the 

 railway cuts between Piercefield and Tupper Lake. These latter 

 are on the edge of the main syenite mass, and show excellently two 

 of the varieties of gneiss concerned, and their relations. These are 

 a green, syenite gneiss and a red, granitic gneiss. The former is 

 exceedingly like some of the very gneissoid phases of the syenite, 

 near at hand. In one cut the red gneiss plainly shows an intrusive 

 contact against the green; in another a pegmatite is at the contact, 

 which repeatedly injects the green gneiss along the foliation planes. 

 The pegmatite is a granite pegmatite, and seems to be a phase of 

 the red gneiss. In both cases the green gneiss, which is quite horn- 

 blendic everywhere, becomes excessively hornblendic near the 

 contact, and this is regarded as a contact phase of the green gneiss, 

 though it is an unusual contact rock. Here is a syenite cut by a 

 later granite, and a large mass of syenite near at hand. It would 

 seem most probable that the two belong together, but they do not 

 look alike, there are some differences in their mineralogy, and some 



