IOWA ACADEMY OF SCIENCES. 
129 
known to the trade, together with the first references to 
the introduction of their names into scientific literature. 
In this sense their enumeration is as geological titles. 
The general geological section of the Carboniferous of 
the Western Interior coal field is about as follows, the 
middle three series constituting what is commonly called 
the coal measures: 
SERIES. 
TERBANES. 
THICKNESS 
IN FEET. 
Oklahoma 
Not here differentiated. 
10 
Cottonwood limestones. 
500 
Atchison shales 
30 
Horbes limestones. 
150 
Platte shales. 
50 
Plattsmouth limestones. 
300 
Missourian. 
Lawrence shales 
35 
Stanton limestones. 
100 
Parkville shales. 
50 
lola limestones 
75 
Thayer shales 
Bethany limestones 
100 
Marais des Cygnes shales. 
aou 
Des Moines. 
Henrietta limestones. 
100 
Cherokee Shales 
275 
Sebastian. 
Spadra. 
Norristown. 
Boonville. 
Arkansan. 
Appleton. 
Danville. 
Millstone grit 
Mississippian i 
Not here differentiated 
1 
The terranes being the stratigraphical units, are the main 
sub-divisions to be regarded in the present connection. All 
appear to be more or less well defined throughout the ser- 
ies in which they occur. Over a greater part of the area, 
the more resistant members — the limestones — form usually 
prominent topographic features. In this role they appear 
as conspicuous ridges or eastward facing escarpments, run- 
ning with many minor sinuosities nearly parallel to one 
another and separated from each other by lowlands which 
are worn out on the softer shales. In consequence, the 
individual layers of the latter are usually so covered with 
talus and other rock waste, and so easily weathered and 
9 
