PETROLOGY-ROCKS OF THE CRIPPLE CREEK VOLCANO. 
105 
K 
This table shows not only the close relation of each rock and each type of 
rock to those on either side of it, but it makes remarkably apparent a very gradual 
change from the Mitre Peak phonolite to the monchiquite. It expresses a con¬ 
siderable range in percentages of the essential oxides from one end of the series 
to the other as follows: 
Si0 2 .. 
At,0 3 . 
Fe 2 0 3 
FeO.. 
MgO. 
Range of 'percentages of essential oxides in roclcs of CApple Creek volcano. 
62.80-:'. 
00 
CaO. 
20. 50-12. 
80 
Xa.O 
5.60- 1. 
GO 
ivi>. 
3.80- 
40 
H.,0. 
7. 30- 
10 
11.20-0.70 
10.00-3.00 
5. 90-3. 00 
2.40- .70 
But in spite of these wide limits, the analyses show a close chemical relation¬ 
ship or consanguinity, not only in these principal constituents, but in the less 
usual or less abundant ones like titania, zirconia, sulphuric anhydride, and chlorine. 
The last two components particularly are characteristic of this rock group. The 
U noticeable percentage of combined water may be attributed mainly to analcite, 
but the fluid inclusions in apatite also account for an appreciable amount. 
Certain features are brought out more clearly when these analyses are converted 
into molecular proportions, as has been done below. The “serial character” 0 of 
this rock group is thus very well shown. 
Molecular ratios of essential oxides in rocks of Cripple Creek volcano. 
I. 
II. 
in. 
IV. 
V. 
VI. 
VII. 
VIII. 
IX. 
X. 
XI. 
XII. 
XIII. 
XIV. 
XV. 
XVI. 
SiC>2. 
0.983 
0.980 
0.983 
0.979 
1.046 
0.990 
0.907 
0.915 
0.906 
0.967 
0.933 
0. 865 
0.831 
0.813 
0. 788 
0.734 
AljOs. 
.201 
.196 
.197 
.192 
.187 
.191 
.186 
.181 
.188 
.174 
.175 
.175 
.174 
.167 
.159 
.126 
Fe2C>3 . 
.010 
.012 
.010 
.014 
.014 
.010 
.018 
.018 
.020 
.022 
.026 
.024 
.037 
.031 
.031 
.029 
FeO. 
.007 
.007 
.009 
.006 
.005 
.017 
.027 
.027 
.029 
.023 
.035 
.047 
.036 
.049 
.040 
.051 
M g o.: 
.003 
.004 
.003 
.009 
.010 
.009 
.025 
.031 
.032 
.039 
.051 
.072 
.075 
.114 
.077 
.180 
CaO. 
.012 
.015 
.019 
.022 
.016 
.035 
.077 
.074 
.080 
.080 
.086 
.100 
.131 
.154 
.127 
.200 
Na 2 0. 
.101 
.151 
.134 
.135 
. 100 
.126 
.111 
.107 
.103 
.094 
.079 
.074 
.084 
.069 
.063 
.048 
K 2 0 
.059 
.060 
. 056 
.060 
.062 
.054 
.052 
.054 
.044 
.045 
.048 
.032 
.036 
.039 
.035 
h 2 o+. 
.087 
.113 
.133 
.047 
.038 
.093 
.097 
.065 
.048 
.061 
.117 
.112 
.102 
.120 
.131 
From these figures certain other ratios may be obtained which also show the 
relations among the various rocks. Because of the definiteness and uniformity of 
composition of the phonolite group, the four phonolite analyses have been averaged 
and the resulting analysis designated by P. The other analyses are numbered 
according to the table on the facing page. 
Ratios of potash to soda in r.ocks of Cripple Creek volcano. 
1.. . 
11.. 
III. 
IV. . 
P... 
V. .. 
VI. . 
VII. 
VIII 
1 
: 2.87 
IX. 
. 1 
: 1.91 
1 
: 2.57 
X. 
. 1 
: 2.14 
1 
: 2.23 
XI . .. 
. 1 
: 1.76 
1 
: 2.41 
XII. 
. 1 
: 1.54 
1 
: 2.54 
XIII. 
. 1 
: 2.62 
1 
: 1.67 
XIV.'. 
. 1 
: 1.92 
1 
2.03 
XV. 
. 1 
: 1.61 
1 
2.06 
XVI. 
. 1 
: 1.37 
1 
2.06 
a Washington, H. S., The igneous complex of Magnet Cove, Arkansas: Bull. Geol. Soc. America, vol. 11, p. 403. 
I 
