A Sketch of the Geology of Texas. 359 
from the hunting grounds of the Indians, is-almost exactly iden- 
tical with that which divides the more modern diluvial and allu- 
vial deposits from the secondary formations. The three points, 
lying in the same straight line, San Antonio di Bexar, New Braun- 
fels, (the German settlement on the Guadaloupe,) and Austin; are 
alike the extreme frontier parts of Western Texas, and. the limit 
of the cretaceous deposits of the upper country t ‘ds the south- 
east. In the. few observations which I have to make, I shall 
therefore separate the particulars relating to the. lower country 
from those bearing upon the secondary formations in the section 
of country lying beyond the just mentioned line. in 
‘The route by which I reached the northwestern section of the 
country, leading through Houston, San Felipe, Austin, Colum- 
bus on the Colorado, Gonzales and Seguin, is nearly devoid of 
any geological interest; you see no solid rock in place through 
the whole distance, excepting irregular layers of a coarse calea- 
Teous sandstone of very modern origin, exposed on the steep 
banks of some of the rivers. The surface is elsewhere a thick 
diluvium: of loose materials consisting either of a fertile vegeta- 
ble mould, or of rounded pieces of hydrate of iron—as over the 
barren section between San Felipe and Columbus—or of sand 
and gravel, as near Gonzales and elsewhere. . 
_» The gravel and sand are of some interest on account of the 
- abundance of fossil wood which they contain at many different 
Places. I saw numerous localities of it between San Felipe on 
the Brazos, and Gonzales, and in the valley of the Colorado be- 
tween La Grange and Austin. This petrified wood is often 
found in large pieces, and it is said that occasionally whole trunks 
of trees are met with, which however I have not myself seen. © 
The fossilization of the wood is generally imperfect, the silex 
tite which it has been turned showing most minutely the ori- 
8inal structure: Most of the wood is dicotyledonous; but not 
having the leisure or the necessary books of reference, I : have 
hot made out the species. I have only observed that in some of 
the wood the fibres are extremely close, and the whole structure 
Very compact, exceeding any tree in the existing flora of Texas. 
_ As the gravel and sand in which most of this fossil wood oc- 
: curs is generally covered by post oak timber, which alone grows 
Sa soil of such sterility, it is a common belief among the far- 
‘Mets of the country that the fossil wood was derived from simi- 
