1881 .] 
247 
[Wadsworth. 
The collections were unpacked by me and the thin sections 
made under my supervision, while Professor Zirkel’s “ Microscop- 
ical Petrography ” with Richthofen’s Memoir was accepted in 
good faith as the basis for the work. It was found, however, that 
not only was it impossible for me to arrange any systematic series 
of sjiecimens by following Professor Zirkel’s work ; but that also 
there appeared in the modern volcanic rocks no diagnostic char- 
acters established at one point in the series by Zirkel, that he had 
not abandoned elsewhere. After trying in vain to make out of 
Zirkel’s work any system that should be applicable to the collec- 
tion under my charge, I visited ISTew York for the purpose of 
reconciling the apparent discrepancies of Volume VI, by a study 
of the actual specimens described. 
Mr. Merrill has endeavored to show his devotion to the interests 
of science, as well as his disinterestedness in this case, by stating 
that his work was done at his own expense. Doubtless this 
remark was made in reference to one of mine 1 which applied 
only to my work upon the collection at Cambridge. The work 
in New York was done not only at my own expense, but also at 
the loss of a much needed vacation. 
On studying the collection of the F ortieth Parallel Exploration, 
not only was the same lack of system observed in the arrange- 
ment of the rocks, and more strongly than before ; but there were 
also many mistakes found even in the determination of common 
minerals, such as quartz, biotite, olivine, etc. Rocks widely differing 
in character had been classed together, while others closely allied 
were placed in distinct groups. Now it is true that many of the 
rocks placed in various groups appear to belong there ; and there- 
fore, as the collection is arranged, the work might appear on 
superficial examination, to have been well done. It seems that 
Mr. Merrill was able to make a partial examination only, but even 
then, taught as he had been by Zirkel himself, he was unable to 
agree in a number of cases with Zirkel’s determinations. 
On the other hand, there was not a slide or specimen in the 
collection, at the time of my visit, that was not examined by me. 
Especial attention was given to the classification and relations of 
1 Bull. Mus. Comp. Zool., 1879, v, 275. 
