254 J. D. Dana on the Green Mountain Quartzite. 
These Archean rocks of the Highland range are exposed to 
view in.a deep cut on the unfinished Hartford & Fishkill Rail- 
road, within a mile of Poughquag. The light-gray gneiss east 
of Poughquag, above referred to, lies to the north of the stage- 
road; while 300 or 400 yards to the south of it, and in sight 
from it, there is a high railroad embankment, leading westward 
into the cut. The Archean rock is a coarsely crystallized 
eiss, containing red orthoclase (feldspar), some white albite 
o possibly oligoclase), and in places a little hornblende, with 
fe magnetic iron. Some portions were a black- 
ish gneiss. The strike is N. 40°-55° E.; the dip is nearly 
vertical, but varies from 65° to the southeastward, to 80° to 
the northwestward, while mostly 70° to 80° to the southeast- 
ward. This gneiss was thus wholly unconformable to that 
before described, and also widely different in its lithological 
characters. Some layers of it at Brewster, fifteen miles to the 
east of south, on the Harlem railroad, contain zircons an 
really a zircon syenite; but they alternate with others that are 
e 
simply gneiss. of magnetic iron ore is worked in the 
4. Quarizite formation.—The quartzite constitutes a northeast 
and southwest ridge on the west side of the Archvean range, the 
The quartzite is in general evenly bedded. While there are 
hard compact layers, many are very thin and friable, looking 
sometimes as if argillaceous, though really consisting of ine 
quartz sand. This finer kind is often a little silvery, with micr 
ceous or talcoid scales, and sometimes contains traces of chlorite. 
The stratification varies but little from horizontality, and sr 
variations are in large undulations toward different pomts 
the compass, the dip being mostly but 5° or 10°, though some- 
times 15°. There is hence no conformability to the Archean 
gneiss, and none to the gneiss, mica schist, or limestone, of the 
