466 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1835. 



apparent immunity, which probably is obtained by all animals feeding 

 on it long enough. 



On bottoms, the most common Composites are Conyza Coulteri and 

 Bigelovia Wrightii. Common also are Helianthus lenticularis, Verbesina 

 encelioides, Perezia Wrightii, Grindelia squamosa, and Clappia suwdwfo- 

 lia; and on alkali soils, the fleshy cheuopods : Suceda fruticosa and de 

 pressa, Spirostachys occidentalis. 



No peculiar vegetation distinguishes the Fall of the Pecos. The 

 stream, rushing through a jungle of Cane-Grass (Arundo Donax), is 

 parted by a rocky island and then tumbles about 20 feet over lime- 

 stone bowlders, its muddy waters breaking into various shades of red 

 and brown. 



At Pope's Crossing, the Pecos is about 25 yards wide and from 1 to 

 3 feet deep, with hard, gravelly bottom. Its banks are still bare of 

 timber, but in places shaded with Cane-Grass. The Canagre (Bumex 

 hymenosepalus) is quite abundant here, as at many other points along the 

 river. 



That part of the Pecos Basin from old Fort Lancaster up to Pope's 

 Crossing, made up largely of barren flats, is about the worst ; the graz- 

 ing is fair enough on many, of the adjoining slopes and hills, but no- 

 where sufficient for profitable cattle raising. Near the latter place the 

 grass improves very much ; on the plains north of it large herds of 

 cattle roam and thrive, and settlements are forming. 



It is worthy of notice that cattle, when accustomed to drink the saline 

 water of the Pecos, prefer it to pure rain water. 



On the fine rolling prairie near the mouth of Delaware Creek, the ex- 

 cellent grass consists of Bouteloua oligostachya, hirsuta, racemosa, erio- 

 poda ; Aristida dispersa ; Setaria caudata ; Triodia acuminata ; Pappo- 

 phorum Wrightii. 



Two of the principal tributaries of the Pecos, Delaware Creek 

 aud Black Biver, are treeless except on their headwaters in the foot- 

 hills of the Guadalupe Mountains ; here are small groves of Cottonwood, 

 Chestnut Oak (Quercus Muhlenberg ii), a small Ash {Fraxinus pistaciarfo- 

 lia), Hack berry, Soapberry, and Willow. They both run through an ex- 

 cellent grazing district. On the bluffs of Delaware Creek were collected 

 a very large and remarkable form of Boerhaavia leiosolena, a new species 

 of Greggia (G. linearifolia, Watson) and a Nama (N. stenophyllum, Gray) 

 not before observed north of the Bio Grande. 



VALLEYS WEST OF THE PECOS. 



West of the Pecos the few running streams found outside of mount- 

 ain districts are naked; they are: Comanche, Leon, Toyah Creeks, the 

 Alamos, San Francisco, and Mara villas. On the forks of the last two 

 may be seen a few clumps of Hack berry, Soapberry, and Willow j scat- 

 tered Cottonwood occur near the head of the Maravillas. 



