Merrill.] 
464 
[April 5, 
therefore think that the rock in this respect is quite as Pro- 
fessor Zirkel has stated, and that, if the rock be identical with 
those specimens from the quarry in California described by Mr. 
Wadsworth, the studies of those rocks should be revised. 
Another rock, No. 276, called by Zirkel a typical dacite is 
regarded by Mr. Wadsworth as an old rock probably long ante- 
dating the Tertiary and which he says, “ would by most 
lithologists be called a quartz or a granite porphyry.” 1 The fact 
seems to be that most lithologists who have already seen and 
mentioned it, Zirkel, King and Hague, have not so called it. The 
rock with its prevailing, often fresh, plagioclase with glass inclu- 
sions, with its quartz also carrying glass inclusions, is in its entire 
habitus not at all like an old ante-Tertiary rock. It seems to me 
to be a typical dacite as Zirkel called it. 
Nos. 277 and 278 are regarded by Mr. Wadsworth as frag- 
mental rocks, of which he says, “ the latter at least is old. 2 ” 
No. 277 is not, to my mind, a well stamped dacite, and is of 
somewhat doubtful character. But No. 278 seems to me to be a 
well marked dacite. By Mr. Wadsworth’s expression “old,” one 
is at a loss to know how old he judges the rock to be, but I think 
it is clearly a Tertiary rock. There are some fragments of another 
rock imbeded in this specimen, but there is nothing to lend to 
this rock the character of a fragmentary rock, in the common 
acceptation of that term. 
Mr. Wadsworth considers the dacites of the Report not hitherto 
mentioned as being, with one exception, No. 279, rhyolitic 
(including felsitic) rocks of various ages. 3 This would include 
Nos. 265, 266, 267, 268, 269, 270, 272, 273, 274, 275; of 
these, on purely lithological, aside from geological, evidence, I 
should consider Nos. 267, 268, 269, 270 to be rhyolites, as it 
seemed to me that orthotomous feldspar predominated over pla- 
gioclase and that the groundmass was generally thoroughly 
rhyolitic in its aspect under the microscope, with characteristic 
axiolitic and sphaerolitic shapes, etc. Still others have rhyolitic 
groundmasses, as No. 265, but this was also remarked by Zirkel. 
(Report, p. 134.) 
1 These Proceedings, Vol. xxi, p. 262. 
2 Ibid., p, 266. 
3 Ibid. 
