IGNEOUS ROCKS. 
59 
Partial chemical analysts of igneous rocks from Iron Springs district. 
[Analyst, Fred Lerch, Biwabik, Minnesota.] 
H. 
I. 
J. 
K. 
L. 
M. 
N. 
SiOa 
53.65 
1.59 
.118 
5.65 
66.20 
2.72 
.117 
3.71 
AI2O3 
P2O5 
.076 
4.56 
.138 
5.58 
.192 
6.49 
■ .090 
4.91 
.087 
Fe 
5.16 
Pa0 5 . 
Fe... 
0. 
P. 
Q. 
R. 
S. • 
T. 
. 133 
5.79 
.060 
2.43 
.074 
2.29 
.040 
2.78 
.032 
1.74 
.124 
4.03 
127 
24 
1 1 . Specimen 46317. 
I. Specimen 46318. 
.] . Specimen 46500. 
Hills. 
K. Specimen 46533. 
L. Specimen 46540. 
M. Specimen 46541. 
N. Specimen 46547. 
O. Specimen 46584. 
Mountain. 
Intrusive andesite. Three 
Same. 
Early trachyte. 
Eightmilt 
Same. 
Same. 
Same. 
Same. 
Same. 
Antelope Range. 
North of Stoddard 
P. Specimen 46502. 
Eightmile Hills. 
Q. Specimen 46503. Same. 
R. Specimen 46476. Latest 
Hills. 
S. Specimen 46477. 
T. Specimen 46504, 
Hills. 
U. Specimen 46380. 
Early tuffaceous rhyolite. 
trachyte. Swett 
Same (pitchstone at base). 
Biotite dacite. Eightmile 
Same. 
Analyses A and B are average andesites, although A is a little too 
high in potash and low in alumina. C is a typical trachyte, while 
D is an andesite forming a subordinate part of the early trachyte 
bed. 
The early rhyolite (E) is too high in lime, owing to secondary cal- 
cite occurring in amygdules. This has been subtracted from the 
analysis and the latter recalculated to 100 per cent. This recalcu- 
lated composition (E') is that of a typical rhyolite. The composition 
of F, as given in the table, is too high in silica and too low in alumina 
for a trachyte. The excess silica is accounted for by secondary infil- 
tration in amygdules, and if this be removed and the composition 
recalculated to 100 per cent the alumina percentage will be brought 
up within the limits. The lack of quartz phenocrysts determines its 
name. 
The dacite (G) is too low in silica for a typical dacite, but the pres- 
ence of quartz phenocrysts determines its name. 
According to Professor Iddings the, presence of trachyte and ande- 
site in the same group of lavas is a rare occurrence, nevertheless 
chemical and mineral compositions indicate that both probably 
occur in the Iron Springs area. 
The analyses represent the general acidic character of the series and 
show a slight range in chemical composition, especially in the silica 
and alkalies. Silica ranges from 58 to 70 per cent, the increase to 
73 per cent in analysis F being due largely to the later cavity fillings. 
The alkalies range from 6^ to 9 per cent, the potash being in excess 
of the soda in all cases. This excess reaches a maximum in '.lie 
trachytes C and F, a fact well illustrated in the mineral composition 
