AUGITE-SYENITE AND GRANITELL. 
121 
Tabulation of the results of a microscopic examination of augite-syenites, &c.—Continued. 
Specimen number. 
762....| North 
Place. 
Lake Superior, 
three miles be- 
low the mouth 
of Split Rock 
River, Minne- 
sota. 
| 
oa 
er 
‘2 : 
A a 
& |g/4 
Sas 
£/s & 
E/S/E 
B/31s| 2 
Oo }n|A 
shore of| NE. | 33 | 55 | 8W.| Highly 
Macroscopic char- 
acters. 
line; rather 
coarse - grained; 
flesh-red; gran- 
ite-like. Feld- 
spar and quartz 
both easily re- 
cognizable to 
the naked eye. 
Microscopic descriptions. 
into fragments of orthoclase 
crystals. Another portion of 
the background, however, 
presents no appearance of 
erystalline structure; buthas, 
throughout, a real or apparent 
spherulitic structure, brought 
out by the radiation of minute 
quartz veinlets and by lines of 
minute ferritic particles. 
Although much of the quartz 
is coarse enough to be seen 
with the naked eye, none of it 
is porphyritic, but all second- 
ary. In this rock we have 
evidently a transition phase 
between the felsitic porphy- 
ries and the more completely 
crystalline granitic porphy- 
Ties, or granitells. 
erystal- | With the exception of some rare 
magnetite areas, this rock is 
completely made up of pink- 
ish, turbid, rather large-sized 
orthoclase and oligoclase and 
quartz. The quartz makes 
up fully half of the section, 
and is often in areas one- 
twentieth to one-tenth inch in 
width ; it is, however, wholly 
secondary, the coarsest por- 
tions often penetrating deeply 
into the mass of an orthoclase 
crystal. Several of the large 
feldspar crystals were ob- 
served to have cores whose 
outlines form abrupt limits, 
beyond which the secondary 
quartz does not pass, a fact 
suggesting the decomposition 
and corrosion of the feldspar 
before the advent of the 
secondary quartz. 
| Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: ii. 
Angles on| 2 . 
opposite| 6% 
sides of ag 
cross-hair.| 
° ° ° 
6 5 ll 
6 7 13 
-_e—— 
