Merrill.] 
470 
[April 5, 
fessor Zirkel said, on page 231 of his Report, “ Between Pea- 
vine Mountains and Virginia Range, a somewhat decomposed 
and bleached basalt occurs (531), which bears macroscopical 
olivines.” Since the handpiece, which I saw, carrying the green 
spots noticed by Mr. Wadsworth, is not at all u bleached ” in 
appearance, but is black, and, with the exception of the greenish 
spots occuring here and there, quite fresh in appearance, I find no 
evidence that this hand specimen was the one of which Zirkel 
was speaking. 
No. 534 Mr. Wadsworth says is a melaphyr. 1 I think that it 
is a basalt, somewhat altered. Nos. 537 and 538 are also re- 
garded by Mr. W adsworth as melaphyrs. 2 They may be, though 
these rocks are so much altered that their determination is diffi- 
cult, as Zirkel remarked. 3 
Mr. Wadsworth says 4 that No. 608 is microscopically a rhyo- 
lite. I find that microscopically it is a glass, and nothing that I 
know of can distinguish, in this case, between acidic or basic 
(i. e. rhyolitic or basaltic) glass but geological relations or chemical 
analyses. Had Mr. Wadsworth adduced either, his statement 
would carry weight. The geological relations, I am told, point 
toward the basaltic glasses. This being so, the specimen is prob- 
abty a true hyalomelan or tachylyte. 
In conclusion, I would state that, in the few cases occuring in 
this paper where I have ventured to suggest a designation to a 
specimen differing from that assigned in Zirkel’s Report, such 
suggestion is made with diffidence on my part, and, as it were, 
under protest, because I do not believe that it is always possible 
to determine rock species by a mere study of the specimen with- 
out regard to field relations. My notes are purely the result of 
laboratory study and therefore likely to be incorrect in such 
cases of difference. 
I cannot but think that simple justice to Mr. Wadsworth’s 
readers calls for as speedy a publication as possible of his full, 
original paper, of which he has stated that only a small portion 
was given in his second paper. With these remarks I pro- 
pose to withdraw from further discussion. 
1 These Proceedings, Vol. xxi, p. 270. 
2 Ibid. 
3 Report, p. 233. 
4 These Proceedings, Vol. xxi. p. 271. 
