BY ROBERT L. .TACK, F.G.S., F.R.G.S. 09 



higher rim ditfering in altitude from the lower, in the former case 

 by not less than 1500 feet, and in the latter by an amount 

 varying from 3000ft. to 5000ft. 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. . . . 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." 

 Mr. Maitland adds : "I am not aware of any observations hav- 

 ing 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 

 inland waters takes place." No doubt there is, but it would 

 take such an extended series of observations to prove it that we 

 can scarcely hope for its accomplishment within the present 

 century. 



The May meeting of the Geographical Society had for its 

 chief object to allow Mr. Gregory an opportunity of discussing 

 Mr. Cox's paper, and Mr. Thomson, as Pi*esident, added some 

 remarks before declaring the discussion closed. As the "Pro- 

 ceedings " have not yet been published, I can only speak from 

 recollection of what took place while I was present. Both 

 speakers agreed in everything, and among others that they had 



