198 
IDDINGS. 
ROCK ANALYSES. 
Rocks of Table I. 
From Electric peak and Sepulchre mountain and the Yellowstone Park 
plateau. The first twenty-one have been published in the paper on this 
region already cited. The last three analyses have appeared in an article 
on Obsidian Cliff by the present writer, in the Seventh Annual Report of 
the U. S. Geological Survey. 
1 . 
2 . 
3. 
4. 
5. 
6 . 
7. 
8 . 
9. 
10 . 
11 . 
12 . 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20 . 
21 . 
22 . 
23. 
24. 
25. 
26. 
27. 
Pyroxene-andesite. 
Hornblende-andesite. 
Pyroxene-mica-diorite. 
Hornblende-pyroxene-andesite. 
Pyroxene-andesite. 
Pyroxene-porphyrite. 
Pyroxene-mica-diorite. 
Hornblende-pyroxene-andesite. 
Pyroxene-mica-diorite. 
Quartz-pyroxene-mica-diorite. 
Hornblende-mica-andesite. 
Quartz-mica-diorite. 
Quartz-mica-diorite. 
Hornblende-mica-andesite. 
Quartz-mica-diorite. 
Dacite. 
Quartz-mica-diorite-porphyrite. 
Quartz-mica-diorite. 
Dacite. 
Quartz-mica-diorite. 
Quartz-mica-diorite-porphyrite. 
Rhyolite. Upper Geyser basin. 
Rhyolite. Tower creek. 
Obsidian. East of Willow park. 
Obsidian. Obsidian cliff. 
Lithoidal rhyolite. Obsidian cliff. 
Obsidian. Obsidian cliff. 
Rocks of Table II. 
From Crandall basin, Absaroka range. Mostly rocks forming a gran¬ 
ular core and dikes cutting basaltic breccia and flows. 
1. Gabbro-porphyrite (core). 
2. Basalt (flow). 
3. Basalt (dike). 
4. Mica-pyroxene-porphyrite (core). 
