FORMATIONS IN SOUTHEASTERN IOWA. 301 
ilar to that at Pontoosac. The sandstones at the same horizon on 
Bear and Price’s creeks in Van Buren county differ in no impor- 
tant respect from those in the vicinity of the Mississippi. 
The brown magnesian limestones —At numerous places on the 
Des Moines River and its tributaries above Belfast, brown mag- 
nesian concretionary limestone is seen resting upon the Warsaw 
shales and limestones, though separated from them by a more or 
less disturbed layer of soft, earthy limestone and arenaceous shale 
inclosing fragments of chert. The magnesian limestones are 
disposed in thick undulating beds, and contain considerable con- 
cretionary chert. These chert nodules average about one to 
two inches in diameter, and on the decay of the limestone show 
a thin layer of green clay lining the cavity inclosing the nodule. 
The nodules usually contain fossil remains in abundance, gen- 
erally in a fragmentary condition, though the limestone in which 
they occur may show very little indication of life. The lime- 
stone is usually blue on first removal, but quickly oxidizes toa 
rusty brown color. In texture, the rock is usually more or less 
vesicular but varies to a compact somewhat earthy limestone. 
The latter phase especially characterizes one or two thin ledges. 
These ledges break down more rapidly on exposure and do not 
weather brown as in the case of the more vesicular portions. The 
latter become arenaceous locally, as on the Des Moines below 
Keosauqua, and on Lick Creek above Kilbourne. At the latter 
place, the indications of cross bedding are marked. The arena- 
ceous element is observed chiefly in the lower beds. The lowest 
bed is marked frequently by a large proportion of siliceous matter 
in irregular masses. These masses are nearly pure white silica 
and are sometimes disturbed and worn as if by wave action sub- 
sequent to consolidation. The greatest thickness of these lime- 
stones observed is twenty feet. On Chequest Creek, they are seen 
to grade upward into a compact, buff-colored limestone known 
locally as Chequest marble. On Price’s Creek west of Pittsburg, the 
lower layers grade horizontally into well marked sandstone indis- 
tinguishable from the arenaceous limestone of the Warsaw beds at 
Belfast, Sonora and elsewhere. The brown limestones are marked 
