8() EXPLOKIXG EXPEDITION FROM SANTA Ffi 



branches is about tlio size of the La I Main; fehey flow through a pretty valley, and arc 

 bordered by thickets of willow and alder, and groves of pine and Cottonwood. A.8 

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

 Populus angustifolia. The immediate banks of the Mancos are at this point composed 

 of the black shales, which overlie the Lower Cretaceous sandstones, containing Ostrea 

 eongesta, Tnoceramus problematicus, &o. 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 Qjos heriondos. Soon after leaving the Mancos, we came upon the 

 I. owei- 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. 'Idle sandstones helow 



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, PopiUus, Sdlix. 

 QuerCUS, &C. After traveling lf> miles, we descended into a narrow valley of erosion, 



traversed by a small (dear 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 generally yellow and coarse, 

 hut alternate with laminated, greenish, ripple-marked layers, beds of greenish and gray 

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

 stems ot 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, Yucca 

 angustifolia. The Dolores rises on the west side of the Sierra de 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 hut narrow valley, several hundred feel below 

 the surface of the surrounding country. This is a Valley of excavation, cut in the 

 Lower Cretaceous rocks, which form bluffs on either side over 200 feet high, in mam- 

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

 fertile, covered with fine grass, with groves of eottonwood 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. ( rreat numbers of flowers ornament 

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

 through. 



The bluffs bounding the river below our cam]) show the following section : 

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

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



