ACADEMY OF NATURAL SCIENCES. 251 



7. Alethopteris, n. sp. ; small fragments of the frond of a splendid new 

 species. From this enumeration it will be seen that there can be but little doubt 

 of the Triassic age of the formation in which these plants occur. A large lot 

 of these plants, collected by M. Eemond, has been recently received, and among 

 them are much better specimens of some of the species noticed by Dr. Newberry, 

 and several quite new ones. These will also be examined, described, and figured 

 within a short time. j. d. w.] 



The strike and dip of the clay shales in the different ravines vary considera- 

 bly, but the dip is usually to the southeast. The superincumbent quartzites are 

 more regular in their inclination. There are dykes of feldspathic rock cutting 

 through both the coal and the shales. 



The following section represents, in an ascending order, the position of the 

 coal-bearing strata in the Canon del Retiro, near Los Bronces. 



1. Coarse quartzites with conglomerates. 



2. Conglomerate, 8 feet. 



3. Argillaceous and schistose grits, 3 feet. 



4. Clay shales, with impressions of plants, 8 feet. 



5. Gray grits, 4 feet. 



6. Bluish clay shales with ferns, 12 feet. 



7. Coal, 2 feet. 



8 Compact black clay shales, 5 inches. 

 9. Coal, 2 feet 6 inches. 



10. Clay shales with leaves, several feet. 



11. Coarse grits. 



Another section, measured at the foot of the Cerro de la Aguja, was as fol- 

 lows. 



1. Compact gray grits. 



2. Gray clay shales with seams of coal and plants, 4 feet 6 inches. 



3. Bluish argillaceous grits, 2 feet 6 inches. 



4. Contorted black clay shales, with seams of coal, 6 feet 6 inches. 



5. Coal, 2 feet 6 inches. 



6. Black, compact clay shales, 3 feet. 



7. Coal, 7 inches. 



8. Carbonaceous clay shales, 8 inches. 



9. Coal, 3 inches. 



10. Clay shales and argillaceous grits. 



[Specimens of the coal brought to San Francisco by M. Eemond, are an- 

 thracite, evidently of superior quality. j. d. w.] 



The middle member of the Triassic series consists of quartzites, or metamor- 

 phic sandstones ; these are both coarse and fine grained, and sometimes brecci- 

 ated. They vary in color, from white to red, and are often much altered in the 

 vicinity of the metalliferous veins. The upper member of the series, as seen in 

 the Canada de la Tinta, is made up of rounded pebbles of black jasper and gray 

 quartzite ; in the Canada de los Mimbres, below Los Bronces pebbles of spec- 

 ular iron are included in the mass. The dip of the formation is very irregular, 

 both in direction and amount. 



At San Antonio de la Huerta, Tecoripa, and San Marcial, argentiferous 

 veins of various ages occur iu the lower and middle members of the Trias. At 

 San Marcial, marine (?) shells are found iu the clay slates, near the silver mines ; 



