Merrill.] 
468 
[April 5, 
Of other rhyolites described in the Report, Mr. Wadsworth 
thinks that No. 340 is a much weathered surface specimen, belong- 
ing to the andesites. 1 This is also my opinion; the feldspars seem 
to me to be mostly triclinic, and are in long shapes. I did not 
find quartz, and the groundmass carries much glass, or half glassy 
substance. 
No. 473 was said by Zirkel to contain no biotite, but Mr. 
Wadsworth says that it does and that it may be seen with the 
naked eye. 2 After careful examination the hand specimen was 
found to contain some five or six minute flecks of biotite. Under 
the microscope I found one fragment of biotite which did not 
appear to belong to the main rock but to an included fragment of 
another rock which also carried several thick apatite sections 
not found, I think, in the main rock. This mica fragment was 
about 0.825 mm. long. Besides this foreign mica I found three 
or four bits of mica in the main rock of which the longest dimen- 
sions were about : 0.187 mm., 0.150 mm., 0.450 mm., 0.337 mm. 
I thought it worth while to insert the particulars concerning 
these mica fragments in order that the importance of Mr. 
Wadsworth’s correction, which he emphasizes with italics, might 
be duly appreciated. It hardly need be remarked that this 
minute quantity of biotite lends no characteristic whatever to the 
rock. 
Nos. 364, 365 and 367 I regard as doubtful cases, so far as a 
simple study of the specimen and thin section, apart from the field 
evidence, is concerned, and of difficult determination. 
Mr. Wadsworth thinks 3 that thin section No. 380 is not fro u 
hand specimen No. 948 (now No. 22,160). I think that the section 
corresponds to the hand specimen No. 22,160. 
Mr. Wadsworth also says: “ No section of No. 386 (913) could 
be found by me, but the hand specimen is evidently a basalt.” 4 
The hand specimen, which is columnar, is of a light brownish tint 
on the weathered surface. The fracture is of a light grayish- 
white color, glistening all about with mica. There seems to be 
nothing basaltic whatever in the handpiece excepting its columnar 
1 These Proceedings, Vol. xxi, p. 268. 3 Ibid. 
2 These Proceedings, Vol. xxi, p. 269. 4 Ibid. 
