76 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 16 
SECTIONS STUDIED AND NOTES THEREON. 
PEAK NEAR CHISPA. 
Section of peak belonging to the Vieja Mountains 6 miles west of south of Chispa. 
(PI. VII; PL XI, fig. l.) 
Feet 
1 23. Massive reddish porphyritic rhyolite, with some fragmental material 4( 
22. Clay 3( 
21. Red sandstone 6( 
20. Grayish rock (probably pyroclastic rhyolite) overlain by clays 4( 
19. Conglomerate and clays 8( 
1 18. Rhyolite breccia, white, gray, green, or pinkish in color 10( 
1 17. Thick ledges of hard whitish or gray rock, greenish in upper portion (rhyo- 
lite breccia) 3( 
16. Conglomeratic sandstone and clays 5C 
15. Whitish rock, probably rhyolitic 34 
14. Clay ? 31 
1 13. Rhyolite breccia, groundmass altered to calcite Si 
1 12. Rhyolite breccia, gray in color, containing considerable basaltic material . . 2. 
1 ll 7 . Amygdaloidal facies of 11, contains many cavities infiltrated with chlorite, 
calcite, zeolites, etc 10 
From IV small stringers run into 12, and there are both necks and small 
masses of the amygdaloid in 12. The rhyolite breccia at the contact is 
very much indurated, while at a short distance above the contact it has a 
much looser texture. 
1 11. Dense, almost black, basalt with feldspar phenocrysts 65 
1 1 0. Fine-grained pink rhyolite breccia, containing considerable basaltic material . 6 
9. Fine-grained material (pyroclastic ?) 60 
8. Conglomerate, underlain by clay 20 
7. Sandstone pebbles at base, grading into dark vermilion-colored clays, con- 
glomerate again above the clay 60 
6. Very coarse conglomerate, containing pebbles of slate, red quartzite, green- 
ish quartzite, cherty limestone, and red eruptive rock 50 
(Just below 6 a much-decomposed greenish eruptive rock was seen, but 
it may not have been in place.) 
1 5. Massive reddish rhyolite, containing in a portion" of the bed vesicles that 
have been filled with chalcedony 20 
4. Sands and clays 40 
3. Sand^and clays, with occasional lenticular masses of conglomerate 60 
2. Lenses of conglomerate 1-5 
1. Laminated sandstone and clays, clays very sandy. The color of the rock is 
greenish, due to the presence of considerable quantities of chlorite ....._ 40 
A small dike, striking east and west and cutting the lower part of 
the above series, was observed. This dike is probably of basaltic 
material. 
The dip where the above section was made is 4°+, S. 50° E. 
This section can be simplified and described as consisting of alternat- 
ing beds of sedimentaiy rocks and lava flows, or beds of rhyolitic 
1 Determined from a study of thin sections by Dr. Lord. 
