Classification of Rocks. — Spurr. 
231 
A?ialyses of rocks of the alaskyte group.* 
SiO. 
TiOg 
COg 
P2O5 
AI2O2 
Fe.Os 
MnO 
BaO 
SrO 
CaO 
MgO 
K.O 
Na.O 
LigO 
HgOat no" .. 
H,0 above no 
No. I. 
77-33 
09 
None 
Trace 
12.55 
.91 
Trace 
Trace 
Trace 
•t7 
. 10 
4.80 
3'9 
Trace 
•15 
■53 
99.82 
No. 2. 
No. 3. 
76.30 
.05 
None 
Trace 
12.50 
1.47 
Trace 
.07 
None 
•f7 
None 
4.67 
3-86 
None 
.18 
•32 
Q9-59 
No. 4. 
67.01 
.10 
None 
Trace 
17.91 
1.30 
Trace 
.60 
•13 
1.86 
.42 
4.56 
5-33 
None 
.16 
.48 
99.86 
No. 5. 
75-84 
.09 
None 
Trace 
13-38 
1-45 
Trace 
Trace 
Trace 
.07 
. 10 
4-73 
3-33 
Trace 
.18 
-71 
99. < 
Total Fe calculated as P'eg O3. 
No. I is one of the characteristic dike-rocks of the Terra Cotta 
range, which is a branch of the T.ordrillo mountains. It is a typical 
alaskyte, being of medium, rather coarse texture, and to the naked 
eye evidently made up wholly of quartz and feldspar. Under the mic- 
roscope the structure is seen to be allotriomorphic granular, and the 
minerals to be quartz and feldspar in about equal proportions, the 
feldspar being chiefly orthoclase, with a little microcline and a little — 
determined b}' Fouque method — anorthoclase. There are no ferro- 
m.agnesian minerals. 
No. 2 is also a typical alaskyte, having in the hand specimen a 
light color and the texture of a fine-grained granite. It is an intrusive 
rock from the Skwentna river, to 10 or 12 miles above its junction with 
the Yentna. Under the microscope the structure is seen to be al- 
lotriomorphic granular and the constituent minerals quartz and felds- 
par in about equal proportions. The feldspar is mostly orthoclase, 
with much microcline. There are no dark minerals except a little 
iron oxide. 
No. 3 is also a dike rock from near the summit of the Chilkoot 
pass. It is also classed from its structure as a simple alaskyte, al- 
though its texture is fine, so that in the hand specimen it has a fineiy 
granular or sugary appearance. The color is light gray. Under the 
microscope the rock resembles at first glance a fine-grained quartzyte, 
♦Analyses by Dr. H. N. Stokes, of the United States Geological Sur- 
vey. 
