Contributions to the Geology of Tevas. 27 
contrary, although not of many species, are abundant. Among 
them Trilobites are especially numerous. Those which I col- 
lected belong to the genera Asaphus and Bronteus. In specific 
characters they differ from many found in the valley of the Mis- 
sissippi, or in other valehenie strata of America. Besides t 
Trilobites,»some indistinct. species of Orthis were found at the 
same locality. Some miles further up this river, at a place where 
the limestone does not exhibit any marks of plutonie action, some 
other genera of fossils are met with, as for instance Euomphalus, — 
Spirifer, ete. Of the latter genus one species was found which is 
closely allied to the Spirifer lynx, Eichw., a fossil shell so widely 
spread in the beds of Trenton limestone of the state of New 
York, and the corresponding strata of the western states. In as- 
cending still higher the valley of the San Saba, we lost sight of 
all Paleozoic strata, cretaceous strata of the same character as 
those which we had seen before, taking their place at the surface, 
and occupying especially all the neighborhood of the old Spanish 
fort. We met Silurian strata again nearer to the mouth of the 
San Saba river. Here they consisted of a white siliceous lime- 
stone, evidently much altered, although not to such a degree as 
to destroy all marks of organic remains. A species of Euompha- 
lus with a great number of whorls, analogous to a species from 
the Silurian strata of Russia, could be distinctly recognized. Still 
further down the river, and about thirty miles from its mouth, 
we found in the narrow valley of atributary of the San Saba 
river, inclined strata of a dark colored compact limestone, with 
layers and nodules of black silex. These beds of limestone 
abound with fossils which evidently belong to the carboniferous 
period, and some of them are even exactly identical with species 
of the carboniferous limestone of the Mississippi valley. Most 
of the species which were observed»in the very short examina- 
tion of the locality, belong to the genera Productus, Spirifer, and 
Terebratula. : 
On our return from the San Saba to Fredericksburg, we crossed 
again the same belt of granitic rocks which we had-seen pre- 
viously after passing the Llano, and did not observe any creta- 
ceous strata before reaching the dividing ridge of the Piedernales 
and Llano. 
The main results of this journey, as well as of former investi- 
gations, may be more clearly exhibited in the following state- 
The immense tract of hilly or mountainous country extending 
from the Rio Grande to Red River, is mostly formed by strata of 
the cretaceous formation differing in their fossil fauna from the 
