Record of Geology of Texas, 1887-1896. 
143 
Hill, Robert T. 
“The Upper 'Cross Timhers. — (From their greater altitude and their posi- 
tion, relative to the flow of the rivers, the more western of the Cross ,Tim- 
bei''s, although geologically lower in the series, is known as the Upper, in 
distinction from the eastern, or Uower. lit extends southward from the 
Indian Territory, through the counties of Montague, 'Wise, Jack, Parker, 
Hood, Erath and Comanche, to near the Colorado river. Its eastern border 
at every point is clearly defined, the adjoining prairie region being invaria- 
bly much higher in altitude. The western border is not so sharply marked, 
but it approximately coincides with the 98th meridian until near the 32d 
degree of latitude, when it bends to the westward, losing its identity by 
Thinning out/ so that the boundary between the .wooded and prairie 
region is not always apparent. The surface soil usually consists of an 
exceedingly fine-grained silieious sand, which is the detritus of the under- 
lying strata. This sand is utterly untenacious, except when wet, and is 
readily distributed by the high winds over the surface so as to effectually 
conceal the underlying strata. A small amount of red clay from a neigh- 
boring .stratum gives to the sand, when mixed with it, a dirt-yellow color. 
******* 
“The character of the soil, .as .aJbove described, is also constant along the 
eastern edge, but is varied along the western half of the timbers by the 
presence of a crumbling, fine-pebble eonglomerate. 
“The Lower Cross Timbers. — (The Lower Cross Timbers are loicated a'bout 
fifty miles east of the upper belt, and extend in a direction approximately 
parallel to it. They are separated their entire length by a prairie region, 
' utterly destitute of timber. The western margin of the Lower 'Cross Tim- 
bers is clearly defined, as is the case with the eastern edge of the Upper 
member; but, instead of being below the level of the prairie it is always 
at a higher altitude. The soil of the Lower Cross Tim'bers, although also 
arenaceous, differs from that of the upper in many respects. It is feru- 
ginous and more fertile, averaging less than ninety per cent, of insoluble 
silica, while that of the upper usually exceeds ninety-seven. The difference 
in fertility of the soils produces a varietal .difference in the flora, the 
trees attaining much larger proportions and the number of species being 
slightly greater. The average width of the Lower Cross Timbers does not 
exceed fifteen miles, and they lose their identity near the Brazos river, at 
Waco’. 
******* 
“The two belts of the Cross Timbers are entirely within the third, or 
Central Denuded iBegion, the eastern border of the lower timbers coinciding 
almost exactly with the western border of the second topographical area. 
The chief geologic agency in .modifying the surface of thi^ region, as before 
stated, has been subaeifial erosion. The only elevation apparent is that 
which is common to' the other areas, and which was due to the rising of 
.the Hocky Mountain axes. The denudation resulting from the subaerial 
erosion has been very great, the whole of the geologic series, from the 
recent to far down into the Carboniferous, having been removed from its 
center or ^place of greatest denudation, ^ * The Tertiary, if it ever 
existed there, has already been removed from this vast area, and the Cre- 
taceous is rapidly yielding — in places entirely gone. This fact being true, 
