52 EXPLORING EXPEDITION FKOM. SANTA FE 



section of the rocks exposed east of Captain Pope's well is as follows, the thicknesses 

 being estimated : 



Feet. 



1. Concretionary tnfaceous Tertiary limestone, cream-colored or white 25 



2. Gray and yellow shales, with concretions of yellowish-brown limestone, 3 to 



5 feet in diameter, with numerous casts of Circeopsis crassa, &c., traversed 

 by bands of blue compact limestone, containing' impressions of Inocera- 

 m-us 1, 000 



3. Grayish or yellowish sandstone 100 



4. Gray or bluish shale, with bands of red, including thin layers of arenaceous 



limestone, containing, as characteristic fossils, Ostrca luf/ubris, Gryplicca 

 Pitcheri, Ammonites percarinatus, Inoceramus problematicus 300 



5. Brownish or yellow thick -bedded sandstone, with layers of shale con- 



taining impressions of dicotyledonous leaves 350 



6. White, fine-grained, calcareous sandstones. 



7. Red calcareous sandstones and marls. 



In this section Nos. 6 and 7 belong to the Trias, and are the equivalents of 

 the red and white calcareous sandstones exposed in the valley of the Pecos and in 

 Apache Canon. 



TEKTIAltY FORMATIONS. 



Tertiary rocks are not a marked feature in the geology of the vicinity of Santa 

 Fd, but they are visible in a great number of exposures, and usually form isolated 

 patches of limited area, the remnants of more extensive deposits, now for the most 

 part removed by surface-erosion, to which their yielding nature has offered little 

 resistance. As is true of the patches of Tertiary lying along the eastern bases of the 

 mountains, these beds are of very unequal thickness in different localities, and, in 

 many instances, are mere local accumulations, filling depressions or excavations in the 

 surfaces on which they were deposited. So far as my observation extended, they 

 contained no fossils. In lithological characters they exhibit a remarkable resemblance 

 to the Tertiary strata of the Arkansas basin ; like those, consisting of beds of calcareous 

 tufa, with bands of more compact tufaceous limestone and conglomerates, in which the 

 pebbles are, for the most part, composed of volcanic, materials, basalt, porphyry, 

 trachyte, and scoria, I have little doubt that these beds have been stratified in fresh 

 water, and that the period of their deposition was one in which volcanic forces were 

 in vigorous action in the region where they occur. As will be noticed in the succeed- 

 ing portions of our geological narrative, no similar deposits were discovered by our 

 party in the region bordering the San Juan and Upper Colorado, though older Terti- 

 aries, probably Eocene, occupy a limited district west of the Nacimiento Mountains, 



