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MUSEUM OF COMPARATIVE ZOOLOGY. 28! 
c 
paragonite schist from St. Gotthard. It is, furthermore, destitute of 
disthene, although he says it contains “excellent large crystals of pale- 
blue disthene." 
His granite porphyries belong in part to granites and gneisses and in 
part to the felsites, and his syenites are old and much decomposed 
andesites, in which the quartz is an alteration product. 
The diorites are partly sedimentary rocks, partly granites and felsites, 
partly old andesites, and the rest are old basalts. 
The so-called hornblende porphyries are somewhat altered andesites, 
and the diabases are mainly altered basalts, but a few are unaltered 
ones, the remainder being altered old andesites. The melaphyrs are all 
old, altered basalts, except one, which is an old andesite. 
The propylites are all altered andesites, with which species their 
chemical composition agrees; and the diagnostic distinctions that Pro- 
fessor Zirkel has placed between the andesites and propylites do not 
hold good even in the specimens that he described, as would have 
been readily seen had he given complete descriptions instead of the 
very imperfect and often inaccurate ones that have been published. 
The distinction between these rocks is simply in the degree of altera- 
tion, and they pass directly into each other. With but two exceptions, 
the quartz propylites are old granitoid, folsitic, and fragmental rocks, 
while the two exceptional ones are altered andesites, in which the quartz 
is an alteration product. Rejecting, then, the so-called propylites 
that are not propylites, the range in silica is from 58.66 per cent to 
64.62 per cent, or about 6 per cent, as shown by Mr. King’s list of 
analyses. 
No line can be drawn between the hornblende and augite andesites, 
but both form one continuous series, Professor Zirkel being mistaken in 
his statement that the augite andesites are younger than the rhyolites. 
Beginning with the andesites, the volcanic rocks have been described 
and arranged very indiscriminately, rhyolites being described in his 
report as trachytes, trachytes as andesites, and rhyolites and basalts as 
trachytes, etc, Only a few of these cases can be pointed out here, — All 
the dacites, with one exception, are rhyolites, felsites, and fragmental 
rocks not belonging to andesites. The exception is an altered andesite, 
in which the quartz is an alteration product. Referring again to Mr. 
King’s tables of analyses, we find the range of silica in the undoubted 
andesites to be from 58.33 per cent to 62.71 per cent, or a little over 
4 per cent. Analysis 140 is that of a rock referred with doubt to the 
andesites. 
