1881.] 
249 
[Wadsworth. 
retrace our steps. Mr. King adopted as the basis of his work on 
the volcanic- rocks, Richthofen’s “Natural System,” which, how- 
ever, in detai] and interpretation the former appears to have car- 
ried out to suit himself. The rocks were classified and arranged 
according; to the ideas of himself and his assistants in the field, 
and, later, Professor Zirkel was invited by him to study the collec- 
tion microscopically. 
All of Professor Zirkel’s previous work had been done from a 
different method of classification ; and it seems to be generally 
understood that, at the time he visited this country, he did not 
believe in the classification adopted by Mr. King. Be that as it 
may, he returned from his visit to Mr. King a professed believer in 
it. Of this visit Professor Zirkel wrote to Mr. King : “ You then 
enabled me to become acquainted with the geological distribution, 
relative age, and reciprocal connections of the rocks ; and if I have 
been able to study their mineralogical and chemical constitution 
from a geological point of view, and to present more than a sterile 
and dry petrographical description, the merit is originally yours* 
# # # You know that when we examined the collection macroscop- 
ically I entirely agreed with the determination and nomenclature 
you and your able colleagues had already arrived at in the field. 
There were only some doubtful occurrences, whose true nature 
could not at that time be decidedly cleared up. Now, after hav- 
ing carefully studied more than twenty-five hundred tliin-sections 
under the microscope, I have only to testify again that your orig- 
inal designations should almost never be altered or corrected.” 1 
After the preliminary examination, a selected collection, I under- 
stand, was taken to Europe, and the sections made there which 
were then studied microscopically. The results of the microscop- 
ic examination, together with much material derived from Mr. 
King and his assistants, were published in the “ Microscopical 
Petrography,” (Yol. VI). According to that work the number of 
specimens reported upon out of a collection numbering 2823 was 
670; this last number however ought to be increased somewhat 
on account of some mistakes made in the numbering in the volume. 
The whole number of thin sections deposited at the time of my 
1 Letter to the Geologist-in- charge, Yol. vi, p. xv. 
