GEOLOGY AND PALEONTOLOGY. 153 
arenaceous, and usually permit the water to percolate throughout their entire 
thickness. 
Springs are abundant in all parts of the group. It would scarcely be an ex- 
aggeration to state that there is an average of one spring for each square mile of 
Dakota territory from Oklahoma to Minnesota. Some of these are mere seepage 
springs, which cease their flow during dry weather, while others have a perennial 
flow. The springs of the group may be divided into two classes: fresh-water 
springs, and salt springs and marshes. The former occur indiscriminately in 
all parts of the formation, while the latter are ordinarily confined to the upper 
layers. 
Something of the nature of the water in the various localities may be learned 
by noticing the names of the smaller streams throughout the regions of outcrops. 
In Ottawa, Republic and Washington counties, Kansas, and in Lancaster 
county, Nebraska, there are streams which have the characteristic name of Salt 
creek, and in Cloud county, Kansas, there is a Salt Marsh creek. In Ellsworth 
county, Kansas, Alum creek and Oxide creek bear testimony to the character of 
the water contained in them. All of these creeks take their rise in the region of 
the upper layers of the Dakota, usually near the Salt Marsh horizon of Logan. 
Saline river owes its name to the fact that it receives much of the drainage from 
these salt creeks. On the other hand, such names as Spring creek and Clear 
creek, which are by no means uncommon in the region, indicate that the stream 
is fed by fresh-water springs, usually from the lower beds. 
ORIGIN OF DAKOTA WATER. 
Three theories have been advanced to account for the water-supply of the 
Dakota. They may be designated as the artesian theory, the sheet-water theory, 
and the local-rainfall theory. It is proposed to outline briefly these three theories, 
and to draw from them such conclusions as seem warranted by facts. 
Perhaps the chief exponent of the artesian theory is Mr. N. H. Darton, of the 
United States Geological Survey. Mr. Darton has spent a number of seasons in 
the field, in the plains and Rocky Mountain regions, and is entitled to speak 
with authority on the subject. In his excellent paper on the “Geology and 
Water supply of Western Nebraska,’’® he discusses the question of deep-seated 
waters, and touches on the subject of artesian water in the Dakota. It should 
be remembered that the Dakota sandstone passes under the more recent Creta- 
ceous groups to the west. These later groups.attain their maximum thickness 
in western Kansas and Nebraska, where the Dakota is probably more than 2000 
feet beneath the surface. The greater part of this thickness is composed of 
Pierre shale, which is impervious to water. The sandstone of the Dakota, con- 
tinuing westward, outcrops along the eastern slope of the Rockies and Black 
hills at an elevation of from 3000 to 6000 feet. The water, passing into the 
porous sandstone at these elevations, flows eastward beneath the Pierre shales, 
and has considerable pressure and head at a great distance to the east. In east- 
ern South Dakota, the artesian wells, which yield a large amount of water, ob- 
tain their supply from the Dakota sandstone. The wells and springs of eastern 
Nebraska are thought to derive their supply from the same source. In this 
region, however, the pressure and head, which gradually decrease as the forma- 
tion approaches the surface, have nearly disappeared. There are several springs 
in the region which are known locally as artesian springs. 
‘‘Sheet water’’ is a term which, in the states of the plains, is used rather 
loosely to indicate a steady and constant supply of well-water. The term is 
52. Nineteenth Ann. Rept. U. 8. Geol. Surv., pt. 4, pp. 719-785. 
