270 
IOWA ACADEMY OF SCIENCE 
The underground waters in the sands, derived partly perhaps from 
the basin of the Niobrara, are brought to the surface by the under- 
lying clays in springs which have assisted in the extending the 
basin toward the south. Hence the capture by the White of some 
important tributaries of the Niobrara. Possibly we may also see in 
this how the Cheyenne extended its tributaries southward at the 
expense of Bad and White rivers, for no doubt the sandy Miocene 
formerly extended more or less over that region with less thickness. 
Less has been said here of these latter streams because data are 
lacking concerning their slopes and other features. 
