26 FOREST RESOURCES OF TEXAS. 



converted into fruit farms, a form of enterprise which is making sub- 

 stantial progress and seems to have a promising future. Nevertheless, 

 even under agriculture the region will need a great deal of forest, 

 though of this inferior quality, for protective purposes, both to con- 

 serve moisture and to prevent erosion, to which the soils are particu- 

 larly susceptible. 



THE POST OAK FOREST. 



In the Lignitic Belt, as we have just seen, the upland timber from 

 Hopkins County on the north and Anderson on the south (the western 

 limit of the shortleaf) to the Black Prairie is mainly oak. This oak 

 timber follows the southwesterly extension of the sands and gravels 

 and clays of the Lignitic Belt far into the Eio Grande Plain — to the 

 sand ridges about Carrizo Springs, for example. But isolated from 

 the main belt are other extensive areas of this type of forest, which in 

 general occurs westward to the one hundredth meridian wherever the 

 geologic formation offers conditions similar to those in the Lignitic 

 Belt — namely, pervious sand and gravel beds and sandy red clay hills. 

 Thus the two areas of special note, the Upper and Lower Cross Tim- 

 bers (see Map I), are of this type, as are also the open forests of the 

 granite region, of the Carboniferous area, and of the isolated gravel 

 terraces such as those above the Colorado River at Austin. In the 

 Rio Grande Plain, however, although the favorable soil conditions 

 continue, the post oak dwindles out a little beyond the Nueces, after 

 having followed the Fayette Prairie formation from east Texas to this 

 point. 



The area of granite exposure, with the carboniferous limestone bor- 

 dering it. and the main carboniferous area north of the granite, with 

 the Upper Cross Timbers, give an almost continuous belt of post oak 

 timber from Gillespie County to the Red River. The Lower Cross 

 Timbers, running from the Red River to the Brazos, along the ninety- 

 seventh meridian, together with numerous smaller tracts of scattered 

 shore-line gravel beds, increase the area of post oak timber west of the 

 ninety-seventh meridian to considerable proportions, and provide a 

 vast quantity of useful, if inferior, construction material over an area 

 in which it is most needed. 



There is more to notice in this type than the mere absence of pine 

 timber. Unlike the types previously described, it is a forest adjusted 

 to arid conditions. It is, in fact, the type which the Atlantic forest 

 assumes when it passes into the arid southwest. Naturally those areas 

 of it which lie so far west as Llano, in central Texas, or Carrizo Springs, 

 in the Rio Grande Plain, mark the extreme degree of change brought 

 about by drought. It will be recalled that in the Lignitic Belt there 

 were species of hickory, Spanish oak, and some of the alluvial bot- 

 tom timber, besides much woody undergrowth, in addition to the pre- 



