Merrill.] 
238 
[October 19, 
fessor Zirkel’s report, 1 and offers contradictory ones based upon bis 
own study of the same collection. It will be sufficent to consider 
only a few of these statements of Mr. W ads worth. On page 285 are 
the words : “ The diorites [i. e., the rocks pronounced by Zirkel to 
be diorites] are partly sedimentary rocks, partly granites and fel- 
sites, partly old andesites, and the rest are old basalts.” This dec- 
laration, it will be seen, disposes of every single specimen pro- 
nounced by Zirkel to be a diorite. It would be necessary, therefore, 
to find only a single one of all of them to be a bona fide diorite in 
order to show that Mr. W adsworth’s assertion is inaccurate ; if sev- 
eral such were found, it would seem that the assertion was probably 
impulsively written. The author has given no numbers of the 
specimens and thin sections which he examined, but has deemed 
it sufficient, up to this time, to refer to the original paper for 
their mention, the publication of which, however, has now been 
delayed some two years. Hence, Mr. W adsworth’ s readers have 
no means of knowing which of these specimens are the “ sedi- 
mentary rocks,” which the “ old andesites,” etc., or even why any 
of them are such, since no reasons by way of diagnoses or other- 
wise are given. What he virtually says is that some thirty-five 
rocks pronounced by Zirkel to be diorites have been erroneously 
determined by that eminent investigator. 
My own examination, covering about half of these diorites, 
rendered Mr. W adsworth’s statement absolutely incomprehensible 
to me. 2 
In so large a collection it is not surprising that confusion has 
occasionally arisen between the thin sections and the hand spec- 
imens now exhibited in the Museum and also within each of these 
1 This report constitutes volume sixth of the Report of the Geological Exploration oj 
the Fortieth Parallel. The specific title of the volume is: ‘‘Microscopical Petrogra- 
phy, by Ferdinand Zirkel.” 
2 Through the courtesy of the officers of the American Museum of Natural History, 
at New York, I was enabled to devote some eight weeks to a most instructive and prof- 
itable, though at best imperfect, study of this collection. At that time the numbers of 
Professor Zirkel’s printed report had no corresponding numbers on either hand-speci- 
mens or thin sections. So wide was the discrepancy between the statements of Pro- 
fessor Zirkel’s report and those of Mr. Wadsworth’s paper, that at first I was led to 
think that this confusion of numbers had something to do with the matter; but 
since one could not have followed the collection at all by the numbers of the printed 
