214 BOTANICAL GAZETTE [SEPTEMBER | 
making a compact oval outline when standing free, and a dense 
interlacing of branches in close formation. Frequently at the 
ground the trunk itself divides into several approximately equal 
members. A pure formation of this juniper occurs character- 
istically where a friable limestone exposure lies almost bare of 
soil except a loose débris collected by the forest itself. Where 
such an outcrop occupies a slope whose angle is sufficient to 
make the friable rock surface unstable, an open cedar forma- 
tion is the only woody vegetation present (fig. 72). 
Aside from the very general use made of cedar in commercial 
ways, it occupies an important relation to moisture and soil 
conditions. Not only is the formation found to occupy areas 
where soil cannot accumulate except for the presence Qf this 
growth, but when cut or burned off it tends ‘to reoccupy the 
ground most vigorously and to encroach upon the other 
species. 
Quercus breviloba formation.— This is the so-called ‘‘ mountain 
shin oak” of central Texas. On the summits of the high divides, 
where a thin soil is underlaid by unbroken limestone, the timber 
vegetation becomes very much dwarfed. In such cases the 
shin oak often becomes the dominant species and sometimes the 
only one, torming scrub thickets known as ‘‘shinneries.” The 
mature plant may not exceed three or four feet in height. A 
familiar illustration of shin oak country occurs on the high 
divide between the San Gabriel and the Colorado rivers in 
Burnet county. 
Quercus Virginiana formation.—This is in reality a dwarfed 
live oak formation which covers lower hill slopes or flats where 
the thin surface covering of black soil is strewn with coarse 
fragments of the broken underlying limestone. Such country, 
from its stony character is known as “hard scrabble,” and the 
timber covering, often almost wholly of dwarfed live oak, is 
dwarfed and gnarled into a fitting counterpart of the ground 
structure (fig. 73). 
ENCROACHMENT OF THE CRETACEOUS TIMBER FORMATION.— 
The forest covering of the erosion area tends not only to renew 
