178 BULLETIN OF THE 
inclusions, plates of kaolin, and limonitic masses, but the boundary is 
less distinct against the clear edge, which surrounds only part of the 
crystal. The microcline twinning is seen in spots irregularly dis- 
tributed among areas of single twinning or without visible twinning. 
The twinning runs into the clear feldspar rim a short distance, then 
dying out; this feldspar of the rim, however, does not stop at the 
clouded edge, but extends into the clouded portion in irregular areas, 
which extinguish together. Outside the entire feldspar grain, but often 
touching it, there are areas of fresh glassy microcline, and also aggre- 
gates of little clear feldspars in rounded grains of the albite type. Lit- 
tle tongues of this fresh microcline penetrate the clastic feldspar grain, 
and little veins of the albitic feldspar also cross its corners. Quartz 
grains and muscovite plates also occur isolated in the feldspar; this 
grain seems to be microcline associated with glassy microcline and albite, 
and possessing a clear boundary, which cannot be separated from areas 
within the cloudy portion. 
The second feldspar (No. A), studied in the same way, had a Sp. Gr. of 
2.578 and indistinct microcline cleavage in the powder. In the slide it 
shows a faint double (microcline) twinning; as before, the central part 
is cloudy with the little kaolin or muscovite plates arranged in parallel 
lines, and also fluid cavities and irregular masses of brown limonite and 
black iron oxide. The core is surrounded on the two long sides by a 
clear glassy border of feldspar, about one eighth the width of the entire 
erain. It has a single multiple twinning, which is parallel to and ex- 
tinguishes with one of the sets of twins in the core ; the boundary be- 
tween the rim and core runs in a general straight direction, although 
jagged in detail. The rim contains flakes of muscovite, droplets of 
quartz, and little singly twinned albitic crystals. At one end of the 
grain, but outside, there occurs a large irregular area of doybly twinned 
microcline, fresh and glassy, and distinct from the cloudy core which it 
touches, the clear rim being absent. This fresh microcline, which is 
evidently the same as that found in isolated areas in the rock, con- 
tains mica and quartz inclusions. It extends as a vein half across the 
clastic grain, quartz and mica mingling with the microcline. At the op- 
posite end of the grain a little vein starts from the outside and entirely 
crosses both the clear rim and the core ; it is at first composed of quartz 
and muscovite, then in the interior it changes to glassy microcline. 
This grain seems to be microcline from the specific gravity and optical 
tests; it has freshly formed microcline adjoining it and crossing it in 
veins ; it has a rim of clear feldspar in optical continuity with the 
