﻿48 NEW YORK STATE MUSEUM 



Alexandria bathylith, though there is a zone between the two in 

 which exposures are poor and infrequent. They are separated 

 from one another in part by tongues of Potsdam sandstone, and 

 in part by low, marshy valleys in which no rock outcrops appear. 

 The exposures, however, cover an area of several square miles, and 

 extend to a distance of at least 3 miles from the edge of the bathy- 

 lith. The schists are everywhere cut by dikes of granite, most 

 numerously as the granite is approached. While chiefly of the Alex- 

 andria granite gneiss, it seems to us that dikes of the Picton gran- 

 ite are also present numerously, though it is difficult to arrive at 

 certainty in the matter. Certainly they are present in the granite 

 gneiss itself. Nowhere else in northern New York have we seen 

 just this type of schists, except as occasional occurrences of small 

 extent and bulk. We are disposed to regard them as contact rocks, 

 produced by the action of the granite upon what were, prior, to the 

 intrusion, somewhat impure limestones. We are disposed also to re- 

 gard the Picton granite dikes as especially influential in the action. 

 It must be frankly stated, however, that there are certain difficul- 

 ties in the way of this view, and they will be later summed up. 



The schists are well banded and foliated and range from light 

 to dark green, or greenish black, in color. They are usually of 

 finely granular texture though these alternate with somewhat 

 coarser grained bands. These latter show poorer foliation and are 

 mottled green and pink in color. Narrow, dark red bands some- 

 times appear, due to subsequent infiltration of ferric oxid. At 

 times the green minerals become scant, and the rock then has a 

 light red to pink shade. Narrow bands of black amphibolite and 

 of finely micaceous schist also appear, and an occasional thin quartz- 

 ite band. But the bulk of the series is of green schist. Granite 

 dikes and dikelets abound everywhere, cutting across or parallel 

 with the bedding, in the latter case often forming a good injection 

 gneiss. The dikes are of fine, granite gneiss, of coarse granite, 

 of yet coarser granite pegmatite, or of quartz, the first most abund- 

 ant. 



In composition these green schists are essentially feldspar-pyrox- 

 ene rocks, the latter of green color and responsible for the general 

 hue of the rock. Actinolite is commonly present, and very abund- 

 ant in some of the bands; it is the only amphibole noted in the 

 schists, except in the occasional amphibolite bands. Epidote is 

 often present, though far less common than the actinolite. Some 

 layers hold frequent, small, light colored garnets. Small, scattered, 

 black tourmalins occur throughout the rock in all exposures. 



