LoGaN. | The Upper Cretaceous. 213 
zon. in some places on account of the local dip of the underlying 
sandstone, the water is forced through the shales and comes to the 
surface in the form of salt springs. In one of the Republic county 
salt marshes an artesian flow was obtained with sufficient pressure 
to lift the water 12 feet high. The line of exposure may be traced 
by such local terms as “Willow Spring,” “Spirit Spring,” ‘Round 
Springs,” “Salt Spring,’ “Marsh Spring,” ete. 
A number of views have been advanced to account for the source 
of the Dakota water. One is that it follows the Dakota from its 
position on the eastern slope of the Rocky Mountains. Another is 
that it is from the Tertiary sheet water. It is not improbable, how- 
ever, that the source of a large part of the water is much nearer 
at hand than even the Tertiary formation. 
The Dakota sandstone is capable of storing a great quantity of 
water and of retaining it for a long period of time. The North 
Smoky Hill Butte, figure 10, furnishes an excellent example of this. 
This butte consists of a mound of shale rising one hundred feet 
above the neighboring surface and capped with layers of sandstone, 
forming with the intervening layers of shale an additional thickness 
of 125 feet. The upper surface of the Mound presents an almost 
level exposure of twelve or fifteen acres. At the point of contact 
between the lower shale bed and the sandstone the water flows out 
in the form of springs. The water from the'springs flows the year 
round. The springs are located at the northeastern point of the 
mound, showing that the dip of the rocks is in that direction. It 
is clearly impossible for the water which supplies these springs to 
have come from a horizon below the sandstone; hence its source 
must have been the rain which fell on the surface. That capping of 
sandstone absorbed the water from the clouds and it trickles out 
from the upper surface of the shale as its own weight brings it to 
that level. Some idea of the amount of water stored may be 
gained from the fact that during three extremely dry years the 
supply of water in these springs did not fail once. 
Terra Cotta Mound, figure 11, is another excellent example of 
the storing power of the Dakota. This mound consists of a bottom 
layer of 100 feet of shale with 30 or 40 feet of sandstone resting 
above. Although its upper surface is only a few acres in extent, yet 
