526 THE GLACIAL LAKE AGASSIZ. 



different depths at which a flow of water was first encountered by four 

 wells in the village of Grandiu, N. Dak. These wells, whose probable 

 relationship in their supplies of water may be nearly as shown in fig. 31, 

 are on an area only about 50 rods in extent, and then- several depths are 

 105 feet, 158 feet, 187 feet, and 248 feet. Either the upper water-bearing 

 beds here are narrow, like a stream course, so that they were not fouud by 

 the deeper wells, or, if they exist as sheets of great width as well as length, 

 they are in some parts thiimed out, allowing the impervious till above to 

 rest on that below. The experience in well-boring here is representative 

 of inequalities in depths of flowing wells near together in many other 

 places. More frequently, however, water is obtained from a nearly uni- 

 form depth throughout a considerable area, and it is then evidently derived 

 from a single broadly continuous stratum. 



FRESH WATER FROM POROUS BEDS OF THE DRIFT SHEET. 



Though the water-bearing gravel and sand inclosed between deposits 

 of till often occm- in narrow veins or in beds which sometimes thin out, 

 even near where they yield copious artesian flows, they must have a great 

 extent in the direction from which the water supply is received, descending 

 from levels higher than the Red River Valley plain, where the flowing 

 wells are situated. At least, this must be the case where the water is fresh 

 or only very slightly saline, as at Grandin and in all the southern part of 

 the valley as far northward as the vicinity of Crookston, in Mmnesota, and 

 Blanchard, in North Dakota, and in a large district of Manitoba, including 

 Winnipeg and the Mennonite reserve east of the Red River. 



Upon the higher lands adjoining both sides of this valley the water of 

 rains is partly absorbed by percolation into the di-ift sheet, chiefly thi'ough 

 the most sandy and gravelly layers. Thence it passes in these porous 

 veins and beds downward to the valley plain, where it is heavily pressed 

 by the head of water tilling their upper portions. When a boring pene- 

 trates the impervious overlying beds of alluvial and lacustrine clay and 

 of till the water usually rises with a strong flow above the surface (fig. 32). 

 If the height and pressure of its head are inadequate for this, it rises in the 



