114 GEOLOGY AIJD PALEONTOLOGY. 



6. Sandstone. A fine-grained, friable, micaceous sandstone^ occurring above the marls and 

 clays, and represented as attaining a thickness of from 100 to 200 feet. 



The sandstone contains nodules of clay, which are often large and flattened, forming an 

 irregular or interrupted layer. These nodules are frequently surrounded by pebbles or small 

 gravel. These pebbles consist of quartz, porphyry, greenstone, jasper, &c., and sometimes 

 form layers of conglomerate. From the evidences of drift action afforded in the specimens, it is 

 probable that the formation may at some points present extensive beds of conglomerate. 



This sandstone is precisely of the same character as the Tertiary sandstone of the Mauvaises 

 Terres of Nebraska. 



T. Coarse sand and small pebbles cemented by calcareous matter, forming a conglomerate 

 which has a thickness of 30 or 40 feet. 



8. Fossil wood — an erratic mass found upon the plains. 



9. Vesicular lava, having the cavities filled with earthy matter, and embracing small shells 

 like Ceritheum, but too imperfect to be specifically identified. 



The table-land occupied by this Tertiary formation forms the plateau in which the rivers take 

 their rise. 



V. Specimens from the Coast JRange. 



1. A somewhat vesicular trap or greenstone, containing spots and blotches of soft green earth. 

 1. Greenstone porphyry. 



VI. — Specimens from the tvesterly part of the Cordilleras. 



1. Chloritic rock, having a compact or scarcely laminated structure. 



2. Chloritic or talco-chloritic rock, with hornblende, etc. 



3. Black mica, with quartz veins. — Pine ridge, 16 miles E. of San Luis Key. 



4. White quartz, with schorl. 



5. Quartz and feldspar ; granitic in its structure, and containing schorl. — Near Santa Isabel. 



6. Feldspathic granite, very similar to the jireceding specimens. — Near Acapulco. 



VII. — Specimens from, the central portion of the dividing range. 



1. Granitic or sienitic rock, composed of quartz with black hornblende in blotches and a 

 little mica. — From the bare peaks of the Cordilleras, near the boundary line. 

 2 Feldspathic granite, somewhat gneissoid. 



3. Feldspathic gneissoid granite. 



4. Gneiss. 



5. Hornblende rock ; dark colored. 



This rock is very similar in character to much of the rock of the Green mountain range. 



6. Fine-grained syenitic rock, with hornblende in crystals on the surface. 



The specimens enumerated above, from 2 to 6 inclusive, are evidently from the same formation 

 of metamorphic rocks in the exposures of the different beds. 



T. Rose quartz ; from a loose mass, though probably derived from this metamorphic belt. 

 8. Black tourmaline ; a loose mass. 



