B. 
GEOLOGY. 
Catalogue of the Geological Collection formed in the Isthmus of 
Tehuantepec by the scientific Commission entrusted with the 
exploration of the Isthmus, and classified by Senor Don Andres 
del Rio. 
SIERRA MADRE (PRINCIPAL CHAIN) AND NEIGHBOURING 
HILLS. 
NON-STRATIFIED ROCKS. 
1. Milk quartz with a resino-vitrous lustre and with the cleavage of the rhom- 
boedron very distinct, found near Chivela. 
2. Decomposed granite near the Hacienda de Tarifa. 
3. Granite found in the descent from the Portillo de Tarifa to the plain of the 
Venta de Chicapa. 
4. Granite boulders in the upper course of the Coatzacoalcos. 
5. Syenite also in boulders in the same spot. 
6. Syenite at the foot of the Sierra, at little less than midway from Niltepee to 
Zanatepec. 
7 Dioritic prophyry, or porphyritic greenstone, in the descent from Guichilona 
to Chihuitan. 
8. Hypersthene rock found in the heights which surround the source of 
the stream Zopiluapa, cutting at intervals the calcareous rock. 
9. Antique porphyry with crystals of felspar, tinted with chlorite and ferruginous 
clay from the hillock of Guichicovi. 
10. Claystone porphyry from the summit of Cerro Atravesado. 
11. Magnetic iron ore from the hills of Niltepee. 
STRATIFIED ROCKS. 
12. Quartz rock found in the descent from the Portillo of Tarifa to the Rancho 
de la Agua Escondida. 
13. Quartz of a chipped texture from the Paso del Ostuta, on the road to Zana¬ 
tepec. 
14. Quartz breccia, resting on the porphyry in the summit of the Cerro Atrave¬ 
sado. 
H 2 
