60 
IRON ORES OF IRON SPRINGS DISTRICT. UTAH. 
tables by the excess of potash feldspar over lime-soda feldspar in 
these rocks. 
The alkalies vary approximately with the amount of silica, as 
follows: 
Variations in alkali and silica in igneous rocks of Iron Springs district. 
F. 
E. 
A. 
C. 
B. 
G - 
D. 
Si0 2 
73.17 
8.90 
70.03 
8.12 
65.29 
7.28 
64.83 
8.42 
63.63 
6.92 
61.05 
7.01 
58.04 
6.34 
The only striking exception to this rule is "C," which is high in 
alkalies and comparatively low in silica. 
The total alkalies vary inversely as the lime with minor exceptions. 
Variations in alkali and lime in igneous rocks of Iron Springs district. 
Alkalies . 
CaO.... 
F. 
C. 
E. 
A. 
G. 
B. 
6. 92 
4.46 
8.90 
1.32 
8.42 
2. 85 
8.12 
2.42 
7.28 
4. 85 
7.01 
5. 40 
6.34 
6. 12 
An increase in the amount of silica and alumina is attended by a 
decrease in iron, magnesia, and lime, illustrated in the following 
table : 
Variations in silica and alumina corresponding to variations in iron, magnesia, and lime 
in igneous rocks of Iron Springs district. 
F. 
E. 
c. 
B. 
G. 
D. 
A. 
Si0 2 and A1 2 3 
86.51 
4.24 
84. 50 
6.18 
81.51 
8.60 
79.27 
12.30 
77.08 
14. S3 
77. 00 
14.94 
76.86 
Fe 2 3 FeO, MgO, and CaO 
12. 49 
The relation between the potash and soda is similar to that shown 
by Professor Pirsson to exist in the rocks of the Highwood Mountains, a 
but the relation between the alkalies and the lime is reversed. The 
definite relation existing between potash, soda, and lime in the 
Highwood rocks, according to Professor Pirsson, must have been 
characteristic of the parent magna, and separates these rocks from 
rocks of other areas and groups them into a clan. The same argu- 
ment may be applied to the rocks of the Iron Springs district. 
The chemical character of the rocks is clearly expressed by the min- 
eral composition. The predominance of potash is indicated by an 
abundance of orthoclase, while the basic feldspar varies in amount 
with the lime, except in the early rhyolite (E), in which the high 
a Pirsson, L. V., Petrography and geology of the igneous rocks of the Ilighwood Mountains, Mon- 
tana: Bull. U. S. Geol. Survey No. 237, 1905, pp. 172-174. 
