302 THE JOURNAL OF GEOLOGY. 
by the presence of the well known and characteristic coral 
Lithostrotion canadense, but this fossil has not been observed in 
the arenaceous portions. An analysis of the magnesian lime- 
stone by Owen" shows it to be a nearly pure dolomite, consisting 
of 56 per cent. carbonate of lime and 37 per cent. carbonate 
of magnesia. Additional analyses are now being made of these 
and associated rocks by the Iowa survey. 
Compact gray limestones—Overlying the magnesian limestones 
at Belfast and on Price’s Creek, but usually separated elsewhere 
by the brecciated formation, is a white or bluish gray compact 
limestone which breaks with conchoidal fracture, and is usually 
characterized by brachiopods in greater or less abundance. 
Among these Spirifera Keokuk, var. littont, Rhynchonella ottumwa, 
Productus tenuicostus are common. The limestone is a nearly 
pure carbonate of lime, fine grained and brittle, and corresponds 
in nearly every particular with the character of the Saint Louis 
limestone as originally described by Shumard. It is sometimes 
affected by considerable quantities of nodular chert, in consid- 
eration of which Owen termed it the Upper Concretionary lime- 
stone. In thickness this formation does not usually exceed 
fifteen feet. 
That portion of these beds which rests directly upon the 
magnesian limestones on Price’s Creek, while in the main similar 
to the higher strata, differ in being of a darker color, and it is 
from one of these that the ‘‘Chequest marble” is obtained, a 
block of which was the contribution made by the citizens of Van 
Buren county to the Washington monument. 
Granular limestone —Associated with the compact limestones 
in places is a formation of granular white or gray limestone which 
is remarkable for the pronounced exhibition of cross bedding 
and ripple marks. These beds evidently represent the limestones 
from this region which have been described as odlitic, but they 
are rather of a granular or sandy texture. In some places they 
contain grains of quartz, though for the most part composed of 
nearly pure carbonate of lime. Intercalated with the thin flaggy 
TOWEN, D.D.: Geol. Sury. Wis., Ia. and Minn. 
