MOVEMENTS OF UNDERGROUND WATER 181 
that the coarser the sandstone and the more porous, the greater will 
be the amount of water available at any given well, 
That the pore space in many cases is larger is evident. For example 
in the Prairie du Chien well, drilled in 1903, for the Sanitarium, a coarse 
bed of sandstone was entered at 720 feet below the surface and con- 
‘tinued down to 805 feet, passing through 85 feet of coarse porous 
sandstone. The pore space of this sand as determined by the writer 
from several samples taken from the well was found to be 30. The 
size of the sand grains were very large, making this 85 feet horizon by 
far the strongest flow of water struck in the well. The average size 
of grain as determined by measuring 1,000 representative grains was 
SO) imax. 
The maximum and minimum dimensions of eleven of the larger 
grains are tabulated below and give a fair idea of the coarseness of the 
sand grains. 
TABLE III 
DIMENSIONS OF SAND GRAINS IN POTSDAM SANDSTONE, PRAIRIE 
DU CHIEN, WISCONSIN 
Mini Di. | Maxi Di. 
mension | mension | Average 
SDisststayott 2.43mm 5-35mm 3.98mm 
Best het Bee acu) 2.30 
Boo nge 2.30 220 2.78 
Lise oRe 2.00 3-30 2.60 
Reeaoor 1.29 3.38 2.34 
Oars 1.80 2.93 2.36 
Wei tees TsO 3.08 2.39 
Seren Ta5iT B22 Boy 
Ons sas I.50 2.84 Baty) 
TOW sve: T.55 2.70 Dele? 
Tseiseve 1.60 2.56 2.08 
2.50 
