GEOLOGY OF THE LONG LAKE QUADRANGLE 467 



There is the further question, involved with the last, whether the 

 granitic gneiss is a member of the general eruptive series, or is a 

 considerably older eruptive. In part it is to be classed as a granite 

 rather than a granitic gneiss, and this granitic portion^ may be 

 younger than the rest or may represent less metamorphosed cores 

 of the gneiss, analogous to the gabbro cores of the amphibolite. 

 There is certainly some younger granite in the mass, but the im- 

 pression given is that most of it is not separable from the gneiss 

 and is simply a less metamorphosed phase of it. 



Ogilvie has recently described from the Paradox Lake quad- 

 rangle, a gneiss which has many features in common with this 

 granitic Long lake gneiss, if indeed it be not identical with it, and 

 regards it as a granite belonging to the general intrusive group and 

 younger than the anorthosite and syenite. 1 That there is a con- 

 siderable body of granite in the region of which this is true, the 

 writer is firmly convinced. But he is equally convinced that there 

 is much granitic gneiss in the region which is much older than the 

 anorthosite, and his present disposition is to refer the Long lake 

 gneiss in the main to that group. It would vastly simplify geologic 

 work in the region if Ogilvie' s interpretation of the Paradox granite 

 could be shown to be generally applicable to the granitic gneisses 

 of the district; but there are difficulties in the way. The anortho- 

 sites and syenites contain not infrequently gneiss inclusions, some- 

 times of amphibolite, and sometimes granite. These are unques- 

 tionably older than the intrusives. Now there are amphibolites 

 and granites associated with the Grenville rocks and the uncertain 

 matter is whether these inclusions are from such rocks, or not. If 

 not they distinctly point to the presence of older bodies of such 

 rocks other than those associated with the Grenville; or else to 

 large bodies of such rocks of which minor offshoots cut the Gren- 

 ville rocks. The writer has not yet obtained any evidence in the 

 region which satisfactorily clears up these points. So the mapping 

 of these rocks as gneiss is merely a makeshift, indicative of lack of 

 exact knowledge respecting their age. 



Grampus gneiss. In the southwestern part of the quadrangle 

 is a mass of gneiss which differs materially from the Long lake 

 gneiss in the considerable diversity shown. It is in association 

 with the Grampus Grenville and shows frequent patches of Gren- 

 ville sediments of various kinds, which are too small to map on 



i N. Y. State Mus. Bui. 96, p. 484 et seq. 



