Wadsworth.] 422 [October 3, 



think all will now admit, even if one specimen did bear cyanite ; 

 and further, that he either mistook the quartz as well as the mass 

 of the mica for paragonite, or else the sections now in the collec- 

 tion are not the original ones. 



I deny that I charged Zirkel, as he says I did, with being unable 

 to determine the sj>ecies to which a rock belonged without being 

 informed of its field characters. (Z. 113.) I said that King's 

 statement implied it (W. 271), but I will now say that if King's 

 statement is correct he proved that in this case where Zirkel was 

 not informed as to the geological age of the rock he was unable 

 to correctly designate it iri his own nomenclature, and Dr. Becker 

 has shown the same thing. I also assert, without fear of contradic- 

 tion, that those who adopt a nomenclature such as Zirkel and Ros- 

 enbusch now do, dependent on the geological age, cannot properly 

 designate their rocks until they are informed of their field char- 

 acter ; also, since many of the eruptive rocks are the latest in the 

 field, that age can. in a vast number of cases never be ascertained, 

 and, therefore, the rock never properly determined in their system. 



It may here be pointed out that Dr. Merrill's statement that I 

 object to calling in field relations to aid lithological conclusions 

 is wrong; for if I have ever insisted on any one point, it has 

 been that the field and laboratory work should go hand in hand, 

 and be performed by the same observer. Dr. Merrill then incor- 

 rectly quotes my statement of what Mr. King's remarks imply, as 

 my belief. I do object to basing a lithological classification on 

 geological age, because I believe such a classification to be un- 

 natural. I object to assigning rocks which are identical to several 

 distinct species, merely because they happen to be in overlying 

 or underlying volcanic . flows. It seems to me perfectly proper 

 to collect field data to aid lithological classification but there is 

 a chance for difference of opinion concerning what data to use ; 

 and it would seem that when the classification is perfected that 

 we ought be able readily to infer the necessary field relations 

 from the lithological characters and the reverse, except in the 

 highly altered rocks. 



Professor Zirkel states (Z. 115), "The members of a series of 

 trachytes are held by Mr. Wadsworth to be basalts. This seems 

 to render it proper to instruct him, that a rock in which sanidin 

 prevails and which does not contain olivine never can be named a 



