1881 .] 
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[Wadsworth. 
tion he professes to have desired as to the exact specimens in 
question. The first (No. 152, Col. No. 1826, VI, p. 81), is very 
greatly decomposed, so much so that the writer does not regard 
it as a suitable specimen for classificatory work. He holds that 
the quartz is an alteration product, and that the present structure 
of the hornblende is also the result of alteration, and not original 
as Zirkel holds it to be. The same may be said of the quartz in 
the second syenite (No. 158, Col. No. 1858, VI, p. 82), while the 
rock itself is much altered. The writer regards these as old and 
altered andesites. 
Diorite. 
The diorites of the Fortieth Parallel described by Zirkel are 
regarded by the writer as a varied body of rocks, having but few 
characters in common, except the hornblende. In part of these 
he holds that the hornblende is an alteration product, and in 
others an original one. Nos. 162 (235), 172 (1497), 173 (1500), 
185 (2221), 188 (1637) are regarded by the writer as old and 
altered andesitic rocks. No. 162 contains much alteration quartz, 
and in No. 185 may be seen the remains of well outlined augite 
crystals, which appear to have been unnoticed by Zirkel. 
The diorite of Kawsoh Mountains (VI, p. 86, Col. No. 688), the 
writer regards as an old basaltic rock — a diabase, macroscopi- 
cally and microscopically. It contains some augite which was 
unnoticed by Zirkel. Nos. 164 (903) and 167 (1386) are regarded 
as metamorphosed fragmental rocks and therefore not properly 
classed as diorites even by Zirkel ; 164 is probably an andesitic 
ash. 
The other specimens of “ diorite ” the writer is inclined to con- 
sider as belonging to the granitic and felsitic rocks. Some cases 
are indeed doubtful, as Nos. 163 (836), 174 (1513), and 187 (2723), 
which are so much altered that their diagnosis is difficult, as 
Zirkel evidently found. In fact it may be stated, that it is believed 
that many of the mistakes arose from the collection of surface 
and altered specimens, which were unfit for the classificatory 
work required. This was a matter of more importance, since 
Zirkel appears to have proceeded, in the larger portion of this 
work, upon the principle that these rocks were created in the: 
PROC BOST. SOC. NAT. HIST. VOL. XXI. 17 FEBRUARY, 1882. 
