ABSAROKITE-SHOSHONITE-BANAKITE SERIES. 951 
highly feldspathic modifications of shoshonite magma, and are 
complementary to absarokite, which represents the least feld- 
spathic modification of the same magma. 
A comparison of the chemical analyses of the rocks of this 
series, besides making evident the relationships already noted, 
also shows what mineralogical differences may obtain for rocks 
of nearly the same chemical composition. Some of these dif- 
ferences have already been described in the case of the leucite- 
bearing varieties. Other differences may be mentioned. 
‘Comparing the shoshonite lava flow from the south base of Bison 
Peak (analysis 1, Table IJ.) with the banakite dike rock from 
Ishawooa Canyon (analysis 3, Table III.), we find in the first, 
abundant phenocrysts of labradorite, augite, and olivine; while 
in the second, numerous phenocrysts of labradorite, but few and 
small ones of augite and olivine. The groundmass of the first 
shows much less orthoclase than that of the second, and no 
biotite, which abounds in the second. The latter contains what 
is probably analcite. The shoshonite lava flow from the south- 
east fork of Beaverdam Creek (analysis 2, Table II.), and 
the shoshonite dike rock from the ridge northeast of Indian 
Peak (analysis 4, Table II.), though nearly alike chemically, are 
quite unlike mineralogically. The first has abundant phenocrysts 
of labradorite, olivine and augite, while the second contains no 
olivine. The groundmass of the second contains some brown 
biotite, which may be secondary, while that of the second con- 
tains much biotite that is primary. In each pair of cases we find 
olivine more abundant in the surficial rock, and biotite more 
abundant in the dike rock, or these minerals may be entirely 
absent in one case or the other. 
Similar rocks in neighboring regions.— Rocks almost identical 
with absarokite occur in the region of Bozeman, Montana, and 
have been described by Professor Merrill,* whose work was 
reviewed in the last number of this Journal.? 
*MERRILL,G. P. Notes on some Eruptive Rocks from Gallatin, Jefferson and Mad- 
ison counties, Montana. Proc. U.S. Nat. Mus., Vol. XVIII., pp. 637-673 (No. 1031), 
Washington, 1895. 
2JOURNAL OF GEOLOGY, Vol. III., No.7, p. 850, Chicago, 1895. 
