190 
IOWA ACADEMY OF SCIENCE Vor.. XXVII, 1920 
Jordan-St. Peter field is the greatest artesian basin in the United 
States. These formations outcrop over 15,000 square miles in 
Wisconsin, Minnesota and Iowa. The rainfall which they receive 
is transmitted readily through their porous strata and percolates 
hundreds of miles beneath the surrounding states. Many of the 
towns -of eastern and northeastern Iowa receive a bountiful and 
excellent supply of water from these stored-up sources. Among 
them we may mention McGregor, Dubuque, Sabula, Clinton, 
Manchester and Charles City. Even points as far distant from 
the outcrop as Keokuk, Centerville, Stuart and Denison have 
artesian wells fed from these great aquifers. 
The sandstones of the Des Moines stage are quite strongly 
mineralized and are not much used for municipal supplies although 
they furnish water to a number of country wells. The Cretaceous 
sandstones supply a number of wells in the area of their extent, 
among them being those at Cherokee and Guthrie Center. Pos- 
sibly also some of the wells at Sioux City are fed from these 
beds. 
The various limestone strata of the state also furnish large 
supplies of water to many shallow wells, to abundant springs 
in the areas of their outcrop and to numbers of fairly deep wells 
which penetrate them for a few hundred feet. Such wells are 
those at Oelwein, West Union, Cedar Falls, Forest City and 
elsewhere. 
It has been estimated that seventy-five per cent of the popula- 
tion of the United} States depends directly on underground 
waters (Mendenhall) and a review of conditions in our own 
state would lead to the opinion that an even greater percentage 
of lowans use this source, since only a relatively small number of 
cities and towns depend on surface supplies such as rivers, lakes 
and impounded waters. The brief discussion here, given will 
show, it is hoped, the importance and value of the ground water 
for domestic and industrial uses and yet it is estimated that the 
amount used annually in the United States is equal to only about 
one per cent of the total flow of the streams of the land for the 
same period of time. 
Use of Ground Waters by Plants . — Turning for a moment to 
consider the use of ground waters by plants: it takes but little 
thought to realize the importance of the underground supplies in 
supporting this part of the living world. Doubtless plants derive 
a portion of their needful moisture directly from the rain as it 
