7^ NEW YORK STATE MUSEUM 



On the outer border of the granite-amphibolite injection zone, 

 about six-tenths of a mile west of the forking Pierrepont road, 

 on the right side of the mouth of a deep V-shaped valley locally 

 known as " The Gulch," is a ledge whose southwest face, perpen- 

 dicular to the banding and the foliation, shows the relationships 

 indicated in figure ii. The ledge is predominantly granite gneiss 

 but its base is amphibohte, and several small detached masses of 

 the latter are scattered in the granite. Three of these are in a plane 

 parallel to the dip, and the spaces between them are filled with 

 granitic material which grades into a rather coarse-textured peg- 

 matite, in all respects identical with that so abundantly intruded 

 parallel to the banding in other parts of this area. The granite and 

 pegmatite are of the type normal to the adjacent portions of the 

 injection zone; the amphibolite also appears to be the same as that 

 known to be derived from the gabbro-diorite a little to the east and 

 similar to that so freely interbanded with the garnet gneiss. This 

 outcrop, unique in that it presents evidence which is not wholly 

 ambiguous, seems therefore to demonstrate that the granite at this 

 point is the younger of the two intrusives. 



It is possible on theoretic grounds that this conclusion does not 

 hold true for all parts of the quadrangle. For example, the am- 

 phibolite which is cut by the granite at this locality may be of 

 other, perhaps metamorphic-sedimentary, origin, and if so the later 

 age of the granite with respect to the gabbro would not be estab- 

 lished. Further, it is possible that the granite in question may not 

 belong to the same period of intrusion as the large granite areas 

 west of the Canton-Russell road, and if so the question would still 

 be unsettled. Practically, however, it is not possible to prove the 

 force of these objections, as the following considerations show. 



Metamorphic-sedimentary amphibolite can not be definitely 

 asserted to be present in the sigmoid belt, but if present, is indis- 

 tinguishable in appearance and relations from the igneous am- 

 phibolite; on the other hand, the amphibolite at one point of the 

 outer periphery of the injection zone is known to be derived from 

 gabbro, and at another point in the interior of the garnet zone, 

 amphibolite of ambiguous petrologic character displays relation- 

 ships with the garnet gneiss which can not be interpreted as other 

 than intrusive. Therefore so far as present data can be relied upon, 

 there is only one type of amphibolite in the sigmoid area, and that 

 is metagabbroic. 



