1895. ] NEW YORK ACADEMY OF SCIENCES. 205 
erable new light on its origin. In thin section (Pl. XVL., fig. 
1) it appears as a rather coarse but very even-grained soda- 
granite, apparently of igneous origin, the quartz often granophy- 
ric (whence the rounding of its grains of which Dr. Bailey 
speaks); the dark silicates are augite and brown and green horn- 
blende, the two latter apparently secondary after augite. The 
feldspar is partly idiomorphic, partly granophyric or granitic. 
Towards the edges of the mass the rock becomes fine-grained, 
and shows in thin section (Pl. XVI., fig. 2) a mass of interlac- 
ing rods of feldspar with comparatively little quartz, and augite 
in small irregular granules. The characters cited are sufficient 
to show that this rock has cooled from fusion. Did it occur in 
the midst of highly metamorphic rocks, gneisses and crystalline 
schists, it might well be supposed that its fusion was but an ex- 
treme phase of metamorphism. But in view of the slightly al- 
tered character of the rocks surrounding it, it seems almost cer- 
tain that the fusion was followed by a notable displacement, and 
the rock is therefore a stranger in its present association and 
must be classed as igneous. The peripheral phases, as far as 
noted, accord with this view; we find there a rock approaching 
a porphyry in structure, instead of a gneiss. How nearly the 
granite is connected with the felsites around it, it is not now 
possible to say. 
Microscopie characters. The rock is an augite-soda-granite, 
containing at most, perhaps, one-third free quartz, and a vary- 
ing amount, sometimes quite small, of ferromagnesian silicates. 
In its central parts it is strongly granophyric (Pl. XVII.); to- 
wards the edges it loses that feature and finally becomes fine- 
grained with a rod-like form to the feldspars, and almost no 
quartz. 
The quartz calls for no especial comment. It is, as noted, 
largely intergrown with the feldspar; when not so, it appears to 
have been the last constituent of the rock to form, never show- 
ing crystal outlines. 
The feldspar is partly a twinned feldspar, apparently anor- 
thoclase, and partly untwinned. Much of it is so altered by 
kaolinization that its nature cannot be determined; the more 
altered parts are made almost opaque by the presence of minute 
red flakes (hematite 7). The untwinned feldspar rarely shows 
erystal outlines and is often intergrown with quartz. The 
twinned feldspar shows an exceedingly fine and regular twin- 
ning with a small extinction angle, and occurs mostly in idio- 
morphic crystals imbedded in the quartz-orthoclase mass. 
From the regularity and fineness of its twinning this feldspar is 
considered to be more probably anorthoclase than a fine grained 
plagioclase. 
