MEXICAN BOUNDARY LINE. 10 7 



11. Compact, light ash-colored limestone, containing cretaceous fossils ; among which are 

 Lima Wacoensis, Trigonia Emoi-yi, Gryphcea Pitcheri, and other species. Camanche crossing, 

 Camanche springs. 



b. Specimens from the Limpia range of mountains, between the Fecus river and Bio Grande. 



12. Brown porphyritic trap rock, with crystals of Adularia. 



13. Coarsely crystalline igneous rock, (trap-like in some parts,) composed in a great propor- 

 tion of crystallized feldspar or Adularia, having a chatoyant lustre on the cleavage faces. This 

 rock forms the central part of the mountain range. 



14 Compact quartz rock, of a slightly reddish tint, with minute cavities. 



15. Compact white opaque quartz, approaching chalcedony in its characters. 



These specimens from the Limpia range are of igneous origin, the quartz rock having heen 

 derived doubtless from the gelatinous silica produced by volcanic waters. We have no evidence 

 from the facts before us that any part of the range consists of Metamorphic stratified rocks. 

 They are mostly of reddish-brown porphyry and a coarse granitic aggregate, of which Adularia 

 forms a large part. Some specimens of milky quartz appear as if due to depositions from hot 

 springs. 



c. Stratified rocks to the northwest of the Limpia range. 



16. Compact, fine grained limestone, dipping to the southwest. 

 Vl. Same as the preceding. 



18. Limestone of similar character to the preceding, containing remains of crinoidal columns 

 and shells. 



19. Similar limestone with remains of shells ; (Brachiopoda, etc.) 



20. Limestone like the preceding, of a grayish blue color, containing fragments of Tere- 

 hratula, etc., (probably Terebratula subtilita.) 



Although these specimens present no well marked fossil species, I am nevertheless quite con- 

 vinced, from the character of the fragments preserved, that the rock is of the age of the upper 

 carboniferous limestone. The condition and character of the rock with the fragmentary fossils 

 is precisely identical with specimens from the neighborhood of the Great Salt lake and other 

 western localities. They contain remains of small Terebratula in like manner ; and the numerous 

 fragments of organic bodies which cover the weathered surfaces indicate sufiiciently that the 

 rock is in great measure composed of similar materials. Some of the specimens are quite com- 

 pact, and others are granular in texture ; they are traversed by minute veins, sometimes of 

 calcareous spar, and sometimes of harder material. 



21. Siliceous tufa, resembling trap tufi". It consists of an aggregation of finely divided 

 siliceous matter, porous or minutely cellular in structure. It is represented as forming dykes 

 in the limestone. Two specimens from Eagle spring. 



22. Specimens similar to the last, but coarsely laminated, and with minute concretions ; 

 brecciated, etc. Eagle spring. 



23. Light-colored amygdaloid rock. Eagle spring. 



24. Porphyritic trap. Eagle spring. 



25. Brown porphyry ; compact. 



