16 NEW YORK STATE MUSEUM 



lar mosaic in which are set feldspar crystals of varying size, 

 whose glittering cleavage faces, on freshly broken surfaces, form 

 the most noticeable characteristic of the rock. At Middleville 

 these are very abundant and large, often reaching an inch and 

 more in length, and the rock is much the coarsest syenite that 

 has been found anywhere in the Adirondack region. In fact, it 

 very strongly resembles in appearance much of the igneous rock 

 called anorthosite, which has wide extent in the eastern Adiron- 

 dacks. Both are composed mainly of feldspar, but the feldspar 

 is of widely different character in the two. That of the anortho- 

 site is apt to show striations, looking like fine ruled, parallel 

 scratches, on the bright cleavage faces, but such striations do not 

 appear on the syenite feldspar. The two differ much in chemical 

 composition also. 



The syenite at Little Falls is more widely and much better 

 exposed than at Middleville, is by no means so coarse, varies more 

 in character from place to place, and in part shows no large 

 feldspars whatever. As shown along the Little Falls and Dolge- 

 ville Eailroad, it was described in a previous report to the 

 state geologist.! South of the Mohawk it is more homogeneous 

 and more usually porphyritic than on the north side.^ The 

 westerly exposures, in and about the city, show considerable red, 

 fine grained, granitic rock cutting the syenite. 



This syenite has undergone extensive metamorphism, so that it 

 has been rendered thoroughly gneissoid, and the finer grained 

 portion of the original rock has been mostly, or wholly, re- 

 crystallized. The large feldspars also have been diminished in 

 size by the breaking away of fragments from their exteriors. In 

 general the Little Falls rock is much finer grained and vastly 

 more gneissoid than that at Middleville. In places at Little 

 Falls the large feldspars themselves have been completely 

 crushed to a mass of fragments, and drawn out into lens-shaped 

 patches, around which the foliation curves, as it does also around 

 the uncrushed, large feldspars. 



^N. Y. state Mns. 20th An. Rep't, p.rSS. 



-A porphyritic igneous rock is one which shows more or less numerous 

 crystals, surrounded by more finely crystalline, or even stony or glassy 

 rock material. 



