1901 | VEGETATION OF WESTERN TEXAS 265 
a shaded zone, or in collecting humus materials. This leaves a 
practically continuous grass floor. It also permits the encroach- 
q ment of sun loving species of the chaparral formations, notably 
mesquite. Thus many miles of the granite area are covered with 
a thick growth of mesquite chaparral, with undergrowth of prickly 
pear and several woody species of the Rio Grande chaparral. 
Aenean 
5.— Quercus grisea and Juniperus formations on an outlying butte of the 
Staked pain, Big springs; common formation on buttes in western part of central 
\ province 
The post oak formation of the Rio Grande plain is, as sug- 
gested, a southwesterly continuation of the timber of the 
Fayette prairie sands (in reality of the east Texas forest belt). 
The southwesterly extension of the formation carries it beyond 
the Nuéces river, but it has been met by a more vigorous expan- 
Sion of the Rio Grande chaparral, which has covered the plain 
as far east as the Guadalupe with a dense mesquite jungle and 
| its accompanying undergrowth of prickly pear. 
XEROPHYTIC LIVE OAK FORMATION OF THE OPEN GRASS PLAINS. 
—That part of Texas lying between the 97th and tooth 
