40 THE GEOLOGICAL STKUCTURE, ETC. 



the great interior regions the water-carrying beds are so arranged 

 that there is only one side of a synclinal trough, the higher rim 

 diflering in altitude from the lower, in the former case by not 

 less than 1,500 feet, and in the latter by an amount varying 

 from 3,000 to 5,000 feet. The strata thus present abundant 

 facilities for the escape of the water absorbed by the strata on 

 the catchment area to the west. In the interior, a continuous 

 discharge is actually visible in many places along the eastern 

 margin of the basin. In the case of the Tertiary beds 

 of the Llano Estacado, north of the Canadian River, this 

 leakage supplies many of the rivers flowing from the Great 

 Plains. The discharge from the Cretaceous Dakota Sandstones 

 is well seen in the valleys of the Missouri, the Big Sioux, the 

 James and the Vermillion rivers, where the water rises through 

 the Glacial Drift in the form of powerful artesian springs and in so 

 •doing affords a means of adding to the supply yielded by many 

 wells sunk in the drift. 



No discharge from the water-bearing strata of the Gulf and 

 Atlantic Border regions is witnessed from the portions of the 

 strata which crop out beneath the sea ; but that such must be 

 the case may be inferred from the fact that the pressure on the 

 coastal deep wells is not nearly so great as it ought to be were 

 the water confined in a sealed basin. The hydrostatic pressure 

 of the body of water stored in the inland portion of the strata 

 has a tendency to force the fresh water outwards and thus 

 cause a permanent seaward flow. This water flows with a 

 velocity due to the difference of level between the intake and the 

 level of discharge, less the frictional resistance of the rock 

 through which it flows, 



I am not aware of any observations having been made as 

 to the salinity of the water along the sea-bottom, but it appears 

 to me that there must be a difference in the salinity in those 

 localities where a continuous discharge of inlaud waters takes 

 place. 



The objection may be raised against the oceanic discharge 

 that the pressure of ocean water would be quite sufificient to 

 force its way into the porous strata. 



" The numerous wells sunk at or near the sea coast (South 

 ^' of England) as that at Worthing 400ft. deep, Margate 374ft. 



