REPORT OF THE DIRECTOR I913 63 



with the garnet-gneiss as country rock; in the case of the Pyrites 

 mass, numerous xenoliths of Grenville limestone and gneisses have 

 been included, among them the narrow belt of pyritous gneiss at 

 Pyrites which is the ore-bearing stratum. 



The pink granite-gneiss occupies broad belts and smaller isolated 

 subcircular areas ; while generally foliated, it is rarely massive and 

 saccharoidal. Pegmatite dikes of simple mineralogical composition 

 are abundantly developed in the western area where they cut 

 through Grenville silicious gneisses. Some of these penetrate the 

 amphibolitic border of the gabbro formation, and the granite is 

 believed therefore, though other evidence is lacking, to be younger 

 than the latter. The granite contains abundant amphibolitic in- 

 clusions; in the absence of satisfactory data as to the derivation 

 of these by the metamorphism of limestone, which nowhere shows 

 contact alteration as distinct from regional, the xenoliths are viewed 

 as inclusions of the earlier basic rocks caught up during the in- 

 trusion of the granite. Inclusions other than amphibolite are 

 absent, and because of the apparent impotence of the granite to 

 produce contact alteration, it is believed that widespread assimila- 

 tion has not taken place in those portions of the magma now 

 accessible to observation. 



The schistosity has a general northeast-southwest strike and a 

 northwest dip of 20 to 40 degrees ; it ordinarily follows the band- 

 ing or strike of the formations, but in numerous instances the latter 

 intersects it at an angle as high as 90 degrees. Pitch, as applied 

 to the directrices of folds of all sizes and to the elongation of 

 mineral groups and individuals, is usually parallel to the direction 

 of average dip, but may depart from it as much as 15 or 20 degrees. 

 In the more western gneisses, on the contrary, it is almost parallel 

 to the strike. On the whole, the axes of folds in the limestone, 

 garnet, gneiss and other formations, as well as the elongation of 

 xenoliths in granite, conform with remarkable constancy to this 

 northwest pitch. 



An important structure is the tilted sigmoidal isocline south and 

 west of Pierrepont, which involves the broad belt of garnet-gneiss 

 already referred to, and its peripheral amphibolitic and granitic 

 injection zone. Its axes correspond to the regional pitch, its axial 

 planes to the regional foliation and its limbs are parallel to the 

 regional trend of the formations. Its greatest measured dimension 

 is over 6 miles in an east-northeast direction; from top to bottom 

 it measures y/> miles, and it is perhaps the largest Precambric 



