1881.] 
265 
[Wadsworth. 
Had Mr. Merrill rejected the analyses under No. 140 (Table 
IX) which are from a rock regarded in the reports as an abnormal 
form, he might have -had six analyses of propylites and six of 
andesites, and perhaps have seen their chemical relations better. 
Andesite. 
The separation of the andesites into hornblende and augite- 
andesites is opposed, for the reason that the two minerals, horn- 
blende and augite, are of diverse origin in these rocks, as set forth 
by the writer in the previous publication. 1 Professor Zirkel’s 
hornblende-andesites usually contain augite and the augite-ande- 
sites, hornblende. The division between them is no more a 
geological one than it is a lithological one, Zirkel’s statement that 
the augite-andesite is younger in age than the rhyolites, being, 
according to King himself, an erroneous one. While Zirkel 
places the augite-andesites as geologically closely connected with 
the basalts, King holds that they are separated from them by both 
the trachytic and rhyolitic eruptions (I, p. 576, VI, p. 219). 
While Zirkel states that the augite-andesites “ will always upon 
merely a macroscopical examination be classed as basalts,” the 
writer holds that such confounding of the two rocks on macro- 
scopic study ought to be comparatively rare, and then as a rule, 
only in the case of specimens closely related to the basalts. 
Herein is one of the striking differences between our methods of 
work and classification. 
Professor Zirkel states that in the andesite, Col. No. 17 (VI, p. 
122), no quartz could be found, but quartz in comparatively large 
amounts was seen by me in the section. This quartz is regarded, 
from its microscopic characters, as an alteration product. 
No. 243 (272) I take to be a volcanic tufa (andesitic) and 
to belong with Zirkel’s clastic rocks. 
Dacite. 
Some of the dacites have been spoken of under the head of 
propylite and need not be referred to here. Of the others No. 
271 (90) I regard as a rhyolitic tufa containing andesitic frag- 
1 Bull. Mus. Comp. Zool. 1879, v, 280, 281. 
