BORDER RELATIONSHIPS 481 



granitic syenite type. This may well be because the one type is easy 

 of recognition and the other not easy to distinguish from the other 

 granite types, except where it can plainly be traced into the syenite by 

 imperceptible gradations. The areal mapping, however, brings out 

 clearly the asymmetric differentiation of the syenite and the limitation 

 of the granitic syenite to the granite-gneiss border. The granite-gneiss 

 is confidently believed to be the older rock, from evidence seen elsewhere 

 in the region and because this older granite-gneiss is characterized by 

 its associated amphibolite inclusions, which are also abundant here. So 

 the utmost confidence is felt in the associations here urged, even though 

 it is appreciated that they fall short of demonstration. 



Border Eelations betvpeen the Syenite and Anorthosite 



Inspection of the geologic map shows that in two localities along the 

 border between these two rocks the syenite has so cut its way into the 

 anorthosite as to cause the disappearance of the entire gabbro border of 

 the latter. The most notable instance is that of the great tongue of 

 syenite which extends eastward from FoUensby pond to the Eaquette 

 river. North and south of this tongue the gabbro border- has a breadth 

 of a mile or more, while east of the tongue there is little sign of it. The 

 tongue is full of inclusions of gabbro and anorthosite gabbro, many of 

 large size, and in the near vicinity of these the syenite becomes much 

 more basic, in precisely the same fashion as it does along the entire 

 border, and in considering the origin of the basic phase these basic 

 fringes around the inclusions are held to have much significance. The 

 syenite here has either cut away or wedged apart the gabbro, and again 

 the inclusions are thought to be helpful in determining which of the two 

 has been done. 



The second area of the sort is along the northern border of the map. 

 Here the evidence is not so conclusive as to the cutting away of the 

 gabbro border, since the main contact line is obscured by drift ; but no 

 gabbro appears anywhere, the exposures nearest the syenite all being of 

 anorthosite gabbro, and this is all shot full of dikes from the syenite, 

 sometimes of large size and of the basic variety of the syenite, while the 

 exposed border of the main syenite mass tends also to the basic type, as 

 it does in fact everywhere along this border. The drift-covered area 

 which conceals the main contact line is most unfortunate, but the rock 

 of the larger dikes is so identical in all respects with that of the adjoining 

 syenite mass, and with that of the great tongue of syenite which cut^ 

 into the anorthosite on the north edge of the map, that the age relations 



