28 C. A. White on the Geology of Southwestern Iowa. 
fully investigated, but is known to lie unconformably upon the 
upper Coal-measure rocks of that region, and is suspected to be 
a part of one Dakota group of Cretaceous rocks, and therefore 
of Mesozoic 
tion are in those directions. They are all found exposed on 
Clanton's ‘fork of Middle river, as far southward as the village — 
of Peru, but the next exposure of rocks to the southward is on — 
the Missouri river water-shed, and belongs to the Biche ove: 
ceous horizon before referred My, but its bed o oes 
pear so far eastward. This s the most ngrtheris! expoutife of | 
rocks on Grand river, and is fre miles from the one last men- 
tioned, and five miles eastward from Afton, the county seat of — 
Union county. Fossils are numerous here in the thin calcare- 
ous bands between the layers of carbonaceous and argillaceous 
dip of the strata, an say makes its exit from the state 
with its bed in the +e ie eee of No. 15 of the Madison 
county section. Immediately w: from Winterset the up- 
’ tely westwar 
per beds also disappear, but somewhat less rapidly. The first 
exposure in that direction, after leaving Middle river at — 
the west line of Madison n eounty, is on the East Nishnabotany — 
pi some forty miles distant; yet so simple is the geology of 
that no hesitation is felt in Aegis a J the strata there 
to about the horizon of Nos. 8, 9 and 10 of the preceding sec- 
particularly since that view is Bortobide ated by observations 
on intervening Ground to the southward. The next important 
* Of the described and identified from —— “ 2 ree 
Marcou’s section at Nebraska Cite by Dr. Geinitz, twent are iates, 
and thirteen ar ; Which two classes of Mollusks perseee the types 
which are principally relied upon by those gentlemen to proee the Permian age of 
boa identification of genera and species, yet I nave:lae able to distinguish of 
