Merrill.] 
242 
[October 19, 
the publication of the full, completed paper, the original paper 
before mentioned. 
Further quotation cannot be necessary to show why Mr. Wads- 
worth’s statements, but more especially his method, seemed im- 
pressive. 
Upon reflecting that Professor Zirkel is generally regarded by 
his own countrymen as first-rate authority in this science ; and 
that he is so regarded in America, as it seems evident from the 
fact that he was selected by Americans from among so many emi- 
nent men of Germany to aid in this work, — a student’s doctor- 
ate dissertation , doing away with a large portion of a great work 
of so great a man by the merest assertions, giving neither reason 
for, nor means of checking, such assertions, had something un- 
common about it. 
In our country, the science of microscopic petrography, al- 
though in a relatively embryonic stage of development, is rapidly 
attracting young students to its fascinating pursuit. This branch 
of study, though founded chiefly in England, has since been 
almost completely captured from English soil and carried into 
Germany, where it has attained its highest development up to the 
present time. Our young students, therefore, have been looking 
to German literature and instruction, of late, as the richest sources 
from which to draw ; and the prominent men of Germany have 
been their prominent authorities. But thyse same students very 
naturally and quite rightly look with confidence to dicta issuing 
from our own university at Cambridge, especially when distinctly 
approved by its assembled Academic Council . 1 Setting aside 
the consideration of justice toward Professor Zirkel, since it 
would be manifestly out of place for me to discuss that point, or 
the fact that the average for the propylites is taken from only six analyses, while that 
for the andesites results from eight; the magnesium oxide average for the propylites is, 
in the same way, about 0.46 per cent, higher than for the andesites. But I understand 
that in these analyses of the andesites are included some proper augite- andesites 
which are generally more basic than the hornblende representatives which alone con- 
cern this point; doubtless these chemical distinctions, though slight at the most, would 
correspond still more fully to the microscopic distinctions if this were not the case. 
These notes are not written with any regard whatever to the mooted question as to 
the feasibility of assigning to propylites an essential distinction from hornblende-ande- 
sites in the general classification of rocks, although it certainly appears that the speci- 
mens of this collection would favor such separation. 
i Mr. Wadsworth’s paper was an abstract of an approved doctorate dissertation. 
