294 The American Geologist. November, 1897 
The separation at 3. was not remarkably distinct, while no 
separation at all distinct could V)e obtained between 3. and 
2.661, and it is therefore considered probable that the rock is 
somewhat altered, and that many of the grains, though so 
small.* are not individuall}^ homogeneous. The separation at 
each of the points 2.661, 2.642 and 2.58 was fairly distinct. 
Microscopically the following minerals were determined 
(named in the approximate order of abundance) : 
1. Orthoclase is quite abundant in irregular grains. Crys- 
tal outline was not observed. The grains are frequently ren- 
dered cloud_y by decomposition, especially to kaolin. Inclu- 
sions of biotite, apatite, quartz and hornblende are common, 
while the very fine gaseous or fluid inclusions are not as com- 
mon as usual. Carlsbad twins of orthoclase occur but rarel}'^. 
Micropegmatitic intergrowths with other feldspars can be 
seen with a high power. 
2.- Biotite is aV^undant, being easily "distinguishable b}'' its 
dark brownish color and strong pleochroism. C'rystal outline 
was not observed. 
3. Andesine-oligoclase is quite common, showing no crys- 
tal outline. Carlsbad twins occur with both parts showing 
albite twinning. It is not certain that some other plagio- 
clase is not present; but it seems impossible, as every grain 
w'hich gave a satisfactory test was very near andesine-oligo- 
clase in character, according to the tables of Fouque.l 
4. Microcline occurs quite freely in irregular grains. It 
usually shows an undulatory extinction, corresponding, per- 
haps, to the irregular nature of the double twinning. It de- 
composes to kaolin, epidote and quartz, while biotite and ap- 
atite appear as inclusions. 
5. Hornblende occurs rather sparingly, perhaps as an orig- 
inal constituent, as no augite has been observed. No crystal 
form was noted. Zonal structure is seen now and then; inclu- 
sions of other minerals are common. 
6. Quartz exists sparingly in irregular grains, never show- 
ing crystal outline. No cleavage has been observed. Inclu- 
.«ions occur, but not as abundantly as is common in quartz. 
*They were put through 72-mesh bolting^ cloth and supported by 100- 
mesh bolting cloth. 
fBulletin de la Societe FraDcaise de Min^ralogie. Paris. 1894. 
XVIII, 428. 
