r48 NEW YORK STATE MUSEUM 



usual augite syenite and is referred to it with hesitation in my 

 field notes. The thin section shows it to depart from the syenite 

 in several respects. The coarse bands are more acid than the 

 rest and probably represent pegmatitic portions. The slide 

 shows some 35^^ of quartz, 10/^ of dark minerals, hornblende show- 

 ing incipient alteration to biotite, magnetite and a little pyrite, 

 and the remainder of feldspar, mainly microperthite. The finer 

 gneiss is characterized by much deep orange titanite and emerald 

 green, pleochroic augite, two minerals quite characteristic of 

 certain red, acid gneisses of the region, which are often closely 

 associated with magnetic deposits. Such red gneisses appear 

 ehortly, going down the riyer, and this rock clearly belongs with 

 them. Otherwise its minerals are as in the coarse rock, though 

 quartz constitutes only some lOfc to 15^ of the whole. The struc- 

 ture is like that of the usual gneiss rather than that of the augite 

 syenite. 



At 2| miles is a cut in red, fine grained gneiss (1001)^ with 

 many pegmatitic and some very hornblendic bands, which is a 

 quite typical sample of the red, titanite gneiss just referred to. 

 It will be more fully described as it occurs at Piercefield, a little 

 beyond. Its minerals are the same as those of the green gneiss 

 of the preceding cut, though it is somewhat more quartzose. A 

 5 foot dike of beautifully fresh, olivin diabase cuts this red 

 gneiss and is of additional interest, since it is the most westerly 

 of these dikes that I have seen in the Adirond'acks. The locality 

 is close to the boundary line between Franklin and St Lawrence 

 counties; and, with the imperfect maps in hand, it was impossi- 

 ble to be certain in which the exposure occurred. If in St Law- 

 pence, it will be the first of these dikes to be noted from that 

 county so far as I am aware. 



At a little over 3 miles is another cut (1008), 60 yardls long. 

 The east half shows a green and black gneiss which is fairly 

 basic, containing much hornblende and considerable augite and 

 magnetite, with also a little bronzite. Kearly half the feldspar 

 is plagioclase, whose character as an acid andesin is indicated by 

 extinctions of 10,'^. The rest of the feldspar is untwinued and 



