38 The American Geologist. Janaan', isooi 
III. The Dakota Sandstone, 
a. History and Description. 
Few geological formations are better known by their fossils 
than the Dakota sandstone. The wealth of perfect dicotyledons 
which it has yielded has noade the name familiar wherever 
geology is studied. The material is for the most part well pre- 
served and the matrix easy to work out. A number of persons 
have at various times made collections in this region. The 
two men, however, who have done more than any others are 
judge E. P. West, formerly of the University of Kansas, and 
"Mr. Charles Sternberg. The "Nestor of American palseo- 
botanists." Leo Lesquereux, has identified more species than 
any other person, although much valuable work has been done 
by Dr. J. S. Newberry, Dr. Lester F. Ward, Dr. F. H. Knowl- 
ton and others. The largest collections are in the United States 
National ^Museum at Washington and in the museum of the 
Kansas State University. It is not the province of this paper 
to discuss the Dakota farther than to speak briefly of its rela- 
tion to the subjacent Commanche, and to name some localities 
yielding Dakota leaves. 
b. Stratigraphy. 
The Dakota sandstone in the Mentor-Marquette region 
rests conformably on the Mentor beds. It consists of alter- 
nating layers of reddish or brow-n sandstone and arenaceous 
or argillaceous shales. The point of separation of the Mentor 
and Dakota has not been sharply defined. On purely lithologi- 
cal grounds the sandstone at the top of the Marquette section 
is typical Dakota but the fossils, which there occur in greater 
abundance than in any other locality known, belong to the 
Mentor. The lower part of the Dakota consists chiefly of 
yellowish, whitish and bluish shales with some layers of rather 
soft sandstone. The first layer which is known to contain 
leaves in any considerable quantity is the massive ledge w'hich 
caps the Smoky Hill buttes and Soldier Cap mound in Saline 
county, although leaves occur more than loo feet below this. 
Above the level of this ledge, w^hich forms the escarpments on 
the hills west of Brookville, sandstones predominate. . The 
ledges vary much in thickness. One on Mulberry creek, some 
