74 NEW YORK STATE MUSEUM 



It nevertheless appears highly probable in the light of (i) its 

 mineralogical composition, already described, (2) its uniform con- 

 stitution within narrow limits over wide areas, (3) its structural 

 relations with fragmentary masses of inclosed amphibolite which 

 have been interpreted in part as Grenville or igneous xenoliths, 

 (4) its significant peripheral association with pegmatite dikes, (5) 

 the larger features of its areal distribution, and (6) its resemblance 

 in all these and other respects to similar Precambrian rocks in ad- 

 joining regions which have generally been conceded to be igneous, 

 that the formation is to be regarded as intrusive into the Grenville. 



Its composition and texture are such as are found in acid, igneous, 

 plutonic rock, and it is inconceivable that a recomposed granite of 

 whatever derivation should have the great bulk and uniformity that 

 are characteristic of this formation. The behavior of the granite 

 with respect to certain amphibolite masses apparently included in it, 

 is particularly suggestive. The features are described in detail else- 

 where (pages 86-88), but the point of most significance for the 

 present discussion is that the granite material was manifestly in a 

 condition of fluidity or great plasticit}- at the moment of fracture 

 of the brittle or highly viscous amphibolite. The evidence of the black 

 schist inclusions favors the view that the granite was at this time in a 

 primar}' magmatic condition, rather than in a state of semiplasticity 

 such as might be induced by regional pressure in the zone of flow- 

 age. The association, in two instances, of a number of radiating 

 pegmatite dikes with the periphery of larger granite masses, and the 

 great abundance of these in the intergranite area northeast of Eddy, 

 warrant belief in their origin by the usual method of difi'erentiation 

 from the neighboring bodies of intruded granite. ^Moreover, the 

 subtriangular shape of the granite mass northeast of Pyrites is 

 difficult to imagine as assumed by any other body of rock than an 

 igneous, bosslike intrusive; unless, indeed, it be conceived that the 

 granite gneiss is itself a sedimentary xenolith in surrounding igneous 

 material. This, however, is manifestly an absurd assumption, and 

 the igneous nature of the granite is rendered extremely probable, if 

 not demonstrated, by this feature of its distribution. All the other 

 granite gneiss of the quadrangle is essentially identical with this 

 in composition and general appearance, and if one mass is igneous, 

 all are. 



In the present-day status of investigation of Precambrian gran- 

 ites, the foregoing attempt to indicate the igneous origin of the 



