104 EXPLORING EXPEDITION FROM SANTA Ffi 



are many castle-like buttes and slender towers, none of which can be less than 1,000 

 feet in height, their sides absolutely perpendicular, their forms wonderful imitations of 

 the structures of human art. Illuminated by the setting sun, the outlines of these sin- 

 gular objects came out sharp and distinct, with such exact similitude of art, and con- 

 trast with nature as usually displayed, that we could hardly resist the conviction that 

 we beheld the walls and towers of some Cyclopean city hitherto undiscovered in this 

 far-off region. Within the great area inclosed by the grander features I have enu- 

 merated, the country is set with numberless buttes and isolated mesas, which give to 

 the scene in a high degree the peculiar character I have so often referred to as exhib- 

 ited by the eroded districts of the great central plateau. Here and there we caught 

 glimpses of the vivid green of the wooded bottom-lands of the river, generally con- 

 cealed by the intermediate and overhanging cliffs." 



The general geological structure of the wide area then seen was nearly as intelli- 

 gible and apparent as it could have been upon closer inspection; the higher mesas 

 everywhere composed of the Upper Cretaceous strata isolated portions of a once con- 

 tinuous sheet; the plateau on which we stood the massive sandstones and conglomerates 

 of the Lower Cretaceous group; while the bottom of the trough of the San Juan, where 

 exposed, showed the blood-red tint of the Triassic rocks. 



Near Camp 34 we descended from the plateau of the Sage-plain and encamped in 

 the valley of the Rito del Sierra Abajo, a few miles above its junction with the San 

 Juan. In this descent we passed over the cut edges of all the members of the Lower 

 Cretaceous group, which afforded me the following section: 



Section of Loiver Cretaceous strata at Camp 34. 



Feet. 



1. Dove-colored calcareous shale, with Gryphcea Pitcltcri, in knolls on No. 2. 



2. Yellow, coarse sandstone, often a conglomerate, with pebbles of black and 



white flint 25 



3. Gray shale, with lignite and silicified wood 12 



4. Yellowish, coarse sand-rock, with pebbles of flint (locally), sometimes mas- 



sive, nearly white, quartzose 50 



5. Green shale 2 



6. Massive, nearly white sand-rock; the same noticed on the Dolores at Tierra 



Blanca, &c 16 



7. Yellowish- white sand-rock, with pebbles of flint 12 



8. Soft greenish-yellow sandstone, massive, but easily decomposed 10 



9. Verdigris-green concretionary, hard calcareous sandstone 2 



10. Green and chocolate shales, with bands of fine argillaceous and calcareous 



sandstone of several colors 30 



11. Soft greenish-yellow sandstone 29 



12. Green, chocolate, purple, pink, and white marls, with concretionary bands of 



similar colors of hard, fine argillo-silicious rock 110 



13. Greenish-yellow sandstone, like No. 11 85 



14. Soft greenish sandstone, decomposing like No. 8 8 



