40 NEW YORK STATE MUSEUM 



suggestive that such an attempt may not be entirely futile. Thus 

 it is thought possible that the garnet gneiss inclosed in the western 

 half of the granite mass southwest of Pyrites, that bordering the 

 northwest side of the granite reentrant northeast of Pyrites, the 

 narrow peripheral belt bordering the south half of this boss, the 

 detached and contorted strata at Little River, the xenolith at Boy- 

 den brook, and the heavier development in the sigmoid area, may 

 have been connected as a continuous formation previous to the 

 periods of intrusion and deformation. There is evidence, presented 

 elsewhere (see page 64), that the Pyrites and Pierrepont gabbro- 

 diorites are connected with each other under Waterman hill; that 

 they form in other words a long, narrow, continuous, bifurcating, 

 sill-like intrustion, subsequently highly contorted. If this is so, it 

 is noteworthy that in a general sense the garnet gneisses all occur 

 at or near the lower, that is, the' southeast, margin of this intrusive. 

 Later contortion of the strata, combined with the mechanical effects 

 of the intrusion of the gabbro-diorite sill, have combined to disrupt 

 the formation into the separate areas now observed : and the sub- 

 sequent emplacement of the blunt half lenslike, half bosslike, body 

 of granite northeast of Pyrites has locally pried the formation away 

 from its close association with the basic sill. As regards the remain- 

 ing garnet gneiss areas near the south margin of the sheet, the data 

 at hand do not warrant making any definite assertions, and a 

 hazardous long-distance correlation like that proposed above will 

 not here be attempted. 



SILICEOUS GNEISSES 



The garnet-free varieties of the gneiss, above referred to, may be 

 regarded, from the point of view of the mere type of rock, as tran- 

 sitional to those which on the map have been plotted as Grenville 

 undivided gneisses. These have their most widespread develop- 

 ment in the west-central part of the quadrangle. The siliceous 

 gneisses are far from being a petrologic unit; but any attempt to 

 map their components as they actually occur in the field would result 

 in a mass of illegible detail. 



For the most part, the group consists of medium-gray to dark or 

 purplish-gray, thin-bedded, schistose rocks, composed essentially of 

 quartz, feldspar, orthoclase, microcline, oligoclase and biotite. The 

 latter lends to the rock its dominant color tone. Red garnet is ordi- 

 narily absent, but may be of sufficient abundance locally to give rise 

 to thin, well-defined beds of a garnetiferous biotite schist. Inter- 

 bedded with these ferromagnesian layers are quartzitic bands and 



