IN THE UPPEK RIO GRANDE EMBAYMENT IN TEXAS. 91 



road come from these water-bearing strata. The San Pedro 

 springs at Del Rio have a head of some 930 feet above the sea 

 and the head of the other springs ranges up to 1075 feet above 

 the sea. If the waterbearing strata can be tapped at points 

 where the level of the ground is below these heads, the water will 

 flow. This is the simple principle of all Artesian basins. The 

 question of such water supply in this case is a question of depth 

 to the water-bearing stratum, a question of elevation of the land 

 surface, and of probable height of the head. 



The head of these waters is not likely to be much lower than 

 the head of their lowest known outlet at Del Rio. Farther to the 

 east it must vary somewhat with the known heights of the natu- 

 ral flows in that direction. For the lands south of the Southern 

 Pacific railroad we must infer that the head of the obtainable flow 

 will range between the two figures given. Comparing these eleva- 

 tions with the elevation of the land, I find that nearh^ all of the 

 land east of Canyon Grande west of Eagle Pass railroad and 

 south of the Imperialist pasture, must be lower than 930 feet. 

 The alluvial bottoms in the two Imperialist pasture must also 

 fall below this elevation in their south halves. On these lands the 

 water can be expected to flow. The question of depth is answered 

 by the measurement already given of the several formations that 

 have been described. If a well were made on the bottom along 

 Canon Chiquito on survey 62, in block 4, the formations to be 

 penetrated would be the following: 



Thickness 

 in feet. 



Upson clay 400 



Austiu chalk 750 



Eagle Ford rock 250 



Buda limestone 75 



Del Rio clay 100—200 



Devil's River limestone 300 



Total 1925 



While absolute accuracy cannot be claimed for these figures 

 the error is not believed to exceed 300 feet either way, and at 

 most the main water-bearing rock cannot lie deeper than 2200 

 feet. For other points the same rock will be found to rise north- 

 ward and to go down to the south at the rate of about 50 feet to 

 the mile. 



