ARTESIAN WELLS ON THE LLANO ESTACADO. 23 
be obtained at the surface from a correspondingly greater depth. We must not expect to gain 
water at the surface from a depth greater than the difference between the elevation of the western 
edge of the Llano and the point of boring. This observation is made on the assumption that it 
is to the western edge of the Llano alone to which we must look for the supply of water. It is 
possible that the strata are supplied with water from the northern or northwestern borders of 
the Llano, and in this case water may be obtained from depths much greater than those men- 
tioned. The difference of elevation of the plain from north to south is not yet known, but, as 
we have already shown, it is probable that the surface gradually rises from the south towards 
the north and west, although the measurements along the 35th parallel, when compared with 
those of Captain Pope, do not exhibit a very striking difference of elevation. 
It is very possible that water-bearing strata may be found nearer to the surface than the 
underlying clay formation—the red marls and clays of the gypseous series; and that basins and 
depressions of the strata, of a comparatively local character, will furnish water at the surface from 
a slight depth. To me, the existence of the springs at the borders of the Llano is the best evi- 
dence that is presented in favor of the presence of water in the strata. Its configuration alone 
does not appear remarkably favorable to the success of deep artesian wells. 
