86 EXPLORING EXPEDITION FKOM SANTA Ffi 



branches is about the size of the La Plata; they flow through a pretty valley, and are 

 bordered by thickets of willow and alder, and groves of pine and cottonwood. As 

 usual, at such high elevation, the cottonwood is all of the narrow-leaved species 

 I'lijtitlttH uiif/tiNtifvlia. The immediate banks of the Mancos are at this point composed 

 of the black shales, which overlie the Lower Cretaceous sandstones, containing (Mrcd 

 c/ii/f/rxla, IiKii-n-ttnniK probfomatieus, &c. Very near camp (19) is a clear, cold spring, of 

 which the water is highly charged with sulphuretted hydrogen ; another of the mineral 

 springs flowing from the dark Cretaceous shales, so common in New Mexico, where 

 they are known as Ojos lieriondns. Soon after leaving the Mancos, we came upon the 

 Lower Cretaceous sandstones, which form the surface-rock to the Dolores. These 

 sandstones are covered in places by detached hills of overlying shales and light-blue 

 limestone, as usual, crowded with their characteristic fossils. The sandstones below 

 are exposed in all the ravines which we crossed, and in nearly every locality where I 

 examined them, I found in them impressions of angiospermous leaves, I'O/HI/HH, Hufi.r, 

 QuercuSj &c. After traveling 15 miles, we descended into a narrow valley of erosion, 

 traversed by a small clear stream, a tributary of the Dolores. The walls of the valley 

 are in places nearly perpendicular, and are composed of the Lower Cretaceous sand-- 

 stones, of which some 200 feet are exposed. These are general! v yellow and coarse, 

 but alternate with laminated, greenish, ripple-marked layers, beds of greenish and gra v 

 shales, and occasional bands of lignite. Nearly all contain the impressions of the 

 stems of plants and dicotyledonous leaves, similar to those so frequently before seen 

 in the same formation. The lowest stratum visible at this point, is a fine-grained com- 

 pact sandstone, very uniform in texture, and as white as loaf-sugar; a most beautiful 

 building material." 



The country lying between the Mancos and Dolores is generally dry and sterile, 

 yet is everywhere covered with fragments of broken pottery, showing its former occu- 

 pation by a, considerable number of inhabitants; it is now utterly deserted. Near the 

 mountains it is pretty well timbered ; farther west, trees become more scattered and 

 smaller, the pines confined to the narrow valleys, the uplands dotted with groves of 

 pinon and cedar, with wide intervals covered with sage-bushes and soap-plant, VIK-CH 

 tntf/ustifolia. The Dolores rises on the west side; of the Sierra do la Plata, many miles 

 north of our route, and is here a clear, rapid stream, as large as the San Juan at the 

 Pagosa. It runs through a beautiful but narrow valley, several hundred feet below 

 the surface of the surrounding country. This is a valley of excavation, cut in tin- 

 Lower Cretaceous rocks, which form bluffs on either side over 200 feet high, in ma.nv 

 places perpendicular. The bottom-lands are nearly level, half a mile wide, and verv 

 fertile, covered with fine grass, with groves of cottonwood and willow, and scattered 

 trees of yellow pine. Near the river the thickets are overgrown with virgin's bower 

 and hop, which form almost impenetrable jungles. Great numbers of flowers ornament 

 the open grounds, generally of the species so common in the valleys before! passed 

 through. 



The blufVs bounding the river below our camp show the following section: 

 1. Soil with rolled gravel and bowlders, drift from the Sierra, de la Plata, princi- 

 pally white and black porphyry like that on the Mancos and La Plata. 



