302 sR. T. Mill— Cross Timbers in Northern Texas. 
ing matrix. They are so friable that. they quickly lose all 
appearance of original stratification on exposure, and were it 
not for railroad-cuts and well-borings through the overlying’ 
Cretaceous limestone, their true stratigraphic position would 
still remain obscure. The pure white sands of this series can 
be traced along the eastern border of the Cross Timbers for over 
a hundred miles. These sands constitute the receiving reser- 
voir for the artesian wells of Fort Worth and Dallas, their 
strata dipping at such an angle under the Grand Prairie, that 
they are reached at a depth of 350 feet beneath the first named 
place, and about 750 at the latter. The detritus of this stratum 
has been distributed over most of the Upper Cross Timbers, so. 
as to obscure the exact contact of the Cretaceous—if the Dino- 
saurian sands be Cretaceous—and the Carboniferous. But 
close inspection will reveal the underlying Carboniferous sands 
and conglomerates in sztu, accompanied by characteristic fos- 
sils. 
West of the Upper Cross Timbers the Texas Pacific road 
traverses the Carboniferous for a hundred miles. In places, 
patches of the Cretaceous are preserved upon it; in others, the 
Carboniferous itself is greatly eroded. Ata point between the 
97th and the 99th meridians the greatest denudation has taken 
place. West of this the succession of the strata is again an 
ascending one. ‘The red beds of the Jura Trias are intercalated 
between the Cretaceous and the Carboniferous on the western 
side of the latter formation. The arenaceous beds are again 
exposed in places, especially at the white sand hills of the 
Llano Hstacado. Traces of the Laramie and fresh-water Ter- 
tiaries may be preserved on the plains, but these are beyond 
the province of this paper. 
With this somewhat lengthy explanation of the relations of 
the topography and stratigraphy of the region, I think the char- 
acter of the two Cross Timbers will now be apparent. It is 
certain that they do not represent lacustrine basins or fluviatile 
channels, but are simply the detritus of arenaceous strata which 
occupy well-defined horizons in the geologic series, and which 
have been exposed by the denudation of the overlying strata. 
The reason why the timber confines itself to these arenaceous. 
belts is also evident. They afford a suitable matrix for the 
penetration of the roots of trees, and a constant reservoir for 
moisture, thus furnishing two of the greatest essentials to forest 
growth. The absence of fertilizing ingredients in the Upper 
Timbers also accounts for the exceedingly scrubby growth of 
the timber, which peculiarity, however, the inhabitants always 
ascribe to the burning of the adjacent prairies. The barrenness 
of the prairies, so far as forest growth is concerned, is owing to 
