Wadsworth.] 424 [October 3, 



appears to have been the first of microscopical lithologists to con- 

 sider olivine essential to the basalts. 1 



My objection to Zirkel's method of establishing nephelite is 

 that from the microscopical examination of a small portion of a 

 rock he should assume that he knew how much olivine there was 

 in the remainder, and that from this he could establish quantita- 

 tive relations. His methods are strikingly in contrast with the 

 accurate ones of Rosenbusch and many others. (Z. 115 ; W. 271.) 



Since Dr. Merrill found in one section that the supposed haii- 

 yne grains were outside of the rock mass and in the balsam, 

 while he is unable to say anything about the other two sections, 2 

 I trust Professor Zirkel will accept his determination. (M. 467 ; 

 W. 267, 268 ; Z. 114 ; B. 286.) That such a mistake could have 

 been made by Zirkel had been strenously denied both in this 

 country and in Europe. The error would not have been so much 

 like that caused by the traditional fly on the astronomer's object 

 glass, if Zirkel's attention had not been so strongly called to 

 these grains as being strange and remarkable forms. It is re- 

 markable that in this discussion those three slides whose numbers 

 were known from Zirkel's manuscript were not immediately ex- 

 amined on the publication of my paper in 1879. If I was wrong 

 in this case it would have then completely overwhelmed my 

 work, while if I had been found to be right it would have gone 

 very far to establish the correctness of my statements regarding 

 other errors. This long silence, coupled with Dr. Merrill's testi- 

 mony, conclusively shows that my work was correct in this point. 

 Since Professor Rosenbusch has suggested to me that the blue 

 grains in my sections were from the emery, it is proper to state 

 that this idea occurred to me at the very first, but microscopic 

 examination then of the corundum and emery used in grinding 

 showed that their grains were of a different character. The only 

 explanation I could find of the included grains is the one I have 

 already given, unless they were in the balsam before it reached 

 the laboratory. 



In the question of the formation of propylite from andesite Dr. 



1 Mikros. Phys. 1877, n, 424. 



2 It is interesting to observe that Zirkel's denial covers only the two sections that 

 Dr. Merrill cannot say anything about, but is silent regarding the third, the supposed 

 haiiyne of which he (Merrill) admits is foreign. 



