Wadsworth.] 
264 
[October 19, 
(propylite) or as an unaltered andesite ; but this does not entitle 
propylite to be regarded as a distinct species any more than the 
altered form of any rock or a decomposing specimen of any 
animal should be. It is at best a variety merely, and not a 
strongly marked one at that. 
Mr. King points to the fact that the propylites are generally 
decomposed (I, p. 557), and it is to be remarked that every one 
described by Zirkelwas more or less decomposed. It is further to 
be noticed, as bearing upon this, that glassy propylites are unknown 
(I, p. 722), and “ a glass-bearing propylitic groundmass has never 
been found” (VI, p. 139). If it is necessary to give names to 
the altered states of rocks and regard them as varieties merely, 
the writer accepts the use of the term propylite ; but he is 
opposed to its erection into a species holding equal rank with 
andesite, basalt, and rhyolite. 
Professor Zirkel states that “ the brown hornblende of the 
andesites never produces secondary epidote ” (VI, p. 112), and 
then points to the alteration of an andesitic hornblende to epi- 
dote later (VI, pp. 130, 133). He states however that no other 
occurrence has been observed. The writer claims that such alter- 
ations are comparatively common in the more altered of the so- 
called andesites, not only in Sierra Nevada rocks, but also in those 
of the Fortieth Parallel collection, described and undescribed by 
Zirkel. 
Of the quartz-bearing propylites, No. 226 (1641) I hold is an 
old felsitic rock ; also that Nos. 228 (1863), 229 (1868) are the 
same as some of the rocks Zirkel has described as granite-por- 
phyry; that No. 227 (1453) is an old, decomposed, fragmental 
rock, while Nos. 230 (1869) and 231 (173) are altered andesites 
containing alteration quartz. They are the only ones, even if 
species are to be founded on alteration characters, that are enti- 
tled to be called quartz-propylites. This then disposes of all of 
the quartz-propylites except No. 232 (317). The writer holds 
that the section Col. No. 317 never came from the rock with the 
label No. 317, but that it was made from some old, altered rock. 
(See also Vol. I, pp. 554, 566 ; Vol. II, pp. 841, 842). My conclu- 
sions regarding these quartz-propylites are borne out by the fluid 
inclusions in the quartz found in them, the chemical analyses, and 
by the fact that it does not appear that their age is known. 
