380 Texas in its Geognostic and Agricultural Aspect. (June, 
Spaniards many centuries ago, has already so exhausted the soil 
of loose, light mineral material, that a rich crop can no longer be 
reckoned upon excepting here and there. 
In this connection the following points may be mentioned. 
Till now it has always been a problem where the great sources of 
the San Antonio river, as also of the Comal and San Marcos, — 
have their origin, and why these throughout the whole year con- 
tinue to break forth from under the rocks with the same force and 
temperature as well as with unvarying clearness. 
Roemer, in his work on the chalk formations of Texas, says, 
that the chalk of the Highlands is proven by its organic remains 
to belong to a somewhat deeper geognostic horizon than that of . 
the Hill-country, and is therefore older, although it lies higher. 
It is suddenly separated, steep and sharp, from the latter. He 
says, furthermore, it is possible that through a fault not appa- 
rent on the surface, the chalk of the Highlands near New 
Braunfels was forced back to the higher level, and he believes that 
such transposition and also the sudden and steep upheaval of the 
Highland, explains the remarkable change in the character of 
the rocks, and that the abrupt breaking forth of the sources of 
the Comal at the foot of the table-land has a close connection 
with it. 
Northward and located somewhat higher there appears in a 
singular manner, almost wholly surrounded by the chalk forma- 
tion of the Highlands, an entirely isolated tract of primitive 
mountain formation, and it is well to observe that this piece was 
lifted up through terrestrial forces after the chalk formations had 
already detached themselves. On this granite are found here 
and there isolated remains of chalk. Before the glacial era the 
entire mass was entirely covered with it, and it was almost com- 
pletely destroyed during this long period, and I might therein 
discover not only a proof of its later upheaval, but also of the 
existence of the glacial era; so also other and not yet solved 
problems may here find a solution. Through the upheaval, the 
volcanic force extended also to the chalk surrounding the granite. 
As already remarked, the chalk of the Highlands is much 
harder than that of the Hill-country; as a collective mass it 
resisted the upheaval, and was therefore lifted up at once with 
the granite: hence the steep declivity at the foot. By the 
a upheaval considerable cavities would be formed in and under the _ : 
