Wadsworth.] 428 [October 3, 



hand specimen " now, what could have been my object in denying 

 it, if such resemblance then existed ; especially when the correla- 

 tion of the field, hand specimen, and section characters of rocks 

 has been a special point with me. In the case of Nos. 280 and 

 281 it is clear to me that Dr. Merrill has either examined speci- 

 mens of a common type of rhyolites, with which his description 

 agrees, which now replace the specimens which I found in the 

 collection in 1878, or else he has devoted his description entirely 

 to the mud and other fragmental portions of the rocks, losing 

 sight of the cementing silica. (M. 463, 464 ; W. 261, 262.) 



Of the trachytes Nos. 289, 823, 324, 325, 327, 329, 330, 

 332 (M. 465, 466 ; W. 266, 267), -which are regarded by me 

 as basalts, except one or two which are allied to the ande- 

 sites, it is necessary that I should have the specimens in 

 hand in order to state what characters led me in each case 

 to take the ground I did. Such apparent inclusions as those 

 Dr. Merrill describes in the quartz are frequently penetrations of 

 the groundmass, etc., and not inclusions in the proper sense ; but 

 without the sections I have no means of ascertaining that, and he 

 may be correct. It is not uncommon for the western basalts to 

 carry quartz, sanidin, and biotite, of course mainly as foreign or 

 secondary, and it is well known that my decisions regarding a 

 rock species are based on the characters of the rock as a whole, 

 and not on a few artificial rules. It has to be remembered at 

 every point that the principles of nomenclature employed by us 

 are entirely different. 



Section 612 x (2699) contained in 1878 considerable well 

 marked and unmistakable olivine ; if the section has since been 

 changed I cannot help it. (M. 466 ; W. 266.) My notes state 

 that No. 473, which Zirkel said contained no biotite, has macro- 

 scopical and microscopical biotite, and I think the rock contained 

 then very much more than Dr. Merrill states ; but even if it did 

 not, it shows a want of accurracy on Zirkel's part in saying that 

 no biotite occurred. (M. 468 ; W. 269.) 



It can be seen that even on Zirkel's principles Dr. Merrill 

 agrees with me that Nos. 196, 197, 198, and 199 of Zirkel's dia- 

 bases are basalts (M. 461 ; W. 258, 259) ; also that Zirkel's " beau- 



l Since this paper was written I have been informed by a lithologist, who had seen 

 the section, that it contains the olivine as stated by myself. 



