THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 57 



normally, except for about a foot away from the contact where it 

 follows the curvature of the latter. Thus the lower half of the 

 amphibolite apparently cuts across the gneiss, but in the upper part 

 is parallel to it. Accordingly, w^iile the evidence may be open to 

 slight suspicion, it is thought to favor the igneous character of the 

 contact, and the interpretation of the garnet gneiss as the country 

 rock for the basic intrusive with local drag at its border. 



It is always unsafe, particularly in Precambrian geology, to gen- 

 eralize from too few data, and it is unfortunate that these two were 

 the only instances where actual nonconformity between the schist 

 and the gneiss could be observed. Such cases may, however, be 

 more common than they appear, for it is hardly probable that they 

 are isolated occurrences. On the other hand, the frequent appear- 

 ance of nonconformable contacts is scarcely to be expected in rocks 

 of such extreme antiquity, which are characterized above all by 

 mutual yielding and accommodation in the presence of a common 

 stress of .long duration. In the absence, therefore, of definite in- 

 dication to the contrary, and in view of the fact that the explanation 

 is not antagonistic to any of the facts observed in the field, but is 

 supported by independent petrographic data, the conclusion seems 

 warranted that the small strips of amphibolite so intimately asso- 

 ciated with the zone of garnet gneiss in the southeast corner of the 

 sheet, have an igneous origin. The possible view that not all the 

 hornblende schist in this vicinity is igneous, but that some of it is 

 sedimentary, seems on the whole less acceptable, inasmuch as the 

 two amphibolites, if there are two, are indistinguishable in appear- 

 ance and in their structural relations to the associated garnetiferous 

 formations, and no mass of amphibolite of demonstrably sediment- 

 ary origin has been discovered in this area. 



Moreover, these schists are intimately associated with, and on 

 the north border of the sigmoid near Pierrepont grade into, a coarse 

 massive feldspathic variety which has so much resemblance to 

 certain phases of the Pyrites gabbro-diorite that it is impossible to 

 resist the opinion that the rock is igneous. Seven-tenths of a mile 

 southwest of Pierrepont, a few rods north of the house on the west 

 side of the road at the foot of the hill, there is an occurrence of rock 

 of this character. It is greenish black, uniformly coarse granular, 

 fairly massive, and of pronounced igneous aspect. The microscope 

 confirms the suspicion aroused by a megascopic examination, for a 

 dark green hornblende, pale green to colorless augite (frequently 



