HORNBLENDE-GABBRO. 57 
new sections from other outcrops. The rocks described in the table have 
been selected to illustrate the different phases of this hornblende-bearing 
rock. The first one is a rock in which the basaltic hornblende is in small 
quantity only. The next three contain more hornblende, and are peculiar 
macroscopically, being mottled black, white and pinkish. They also carry 
a good deal of original quartz. The last two are black rocks, in which the 
hornblende makes up most of the section. Abundance of coarse apatite, 
presence of a low-angled plagioclase, of orthoclase, and of original quartz 
seem to be prevailing characteristics. 
Tabulation of observations on hornblende-gabbro. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
u 
oO * ¢ 
2 a Macroscopic char- | Constituents as determined by | in sections cut 
g Place. 3 acters. microscope, in order of age. at random in 
A 3) 3 the zone O: 74. 
a 2 & — 
3 Bg fa Angl on 
a ngles on| 2 
B:| 2£/8/4a|¢ opposite | 3 
3 SE /s|e& i My f| a2 
EI Suliouliva sides 0: A 
a Se lala] cross-hair.| B © 
° ° ° 
137 W.| Ashland County, |N.W.| 35 | 45 |4 W.| Medium-grained; | Apatite, in large crystals, very | 12 17 29 
Wisconsin. cor. dark greenish- abundant; labradorite, incrys- | 19 21 40 
gray. tals often much rounded, quite | 24 21 45 
fresh; orthoclase (?) ; magnetite 
or titanic iron, very large and 
abundant; augite, very abund- 
ant, in very large, rounded par- 
ticles between the feldspar 
grains, only rarely showing 
the diallage cleavage, partly 
fresh, partly altered by spots 
and streaks of a greenish fee- 
bly dichroic or non-dichroic 
substance; brown, intensely 
absorptive, and dichroic horn- 
blende, not very abundant, oc- 
curring partly away from the 
augite—but like it between 
the feldspar grains—and partly 
in patches within the areas of 
the altered augite, in such a 
manner as to suggest its sec- 
ondary origin; uralite, in little 
streaks within the altered 
- augite. 
ee 
