Coal Measures of Central loiva — Keyes. 397 
ures of micaceous sandstone and the associated shales and 
clays, at Des Moines; White's f remarks upon this regional geol- 
ogy are also few. The meagerness of both of these accounts 
is due largely to circumstances entirely beyond the control of 
those engaged in the geological study of Central Iowa. The 
cenological features in the vicinit}'^ of Des Moines have re- 
ceived considerable more attention, and many important de- 
tails disclosed.§ Recently there have also appeared some notes 
on local palaeontology .J 
The topographv of Polk county is essentially characteristic 
drift, except in the immediate proximity of the two principal 
streams, where through the lower part of the middle — and the 
upper portion of the lower coal measures the Des Moines and 
Racoon rivers have corraded their channels nearly one hundred 
feet below the general level of the sedimentary strata of the 
viciuity. Aside from the surface deposits the rocks exposed in 
Polk county belong to the age of the coal measui'es — the mid- 
dle (of White and St. John) and the lower. No sub-carbon- 
iferous strata are naturally exposed within the limits of the 
county, but, inasmuch as the St. Louis limestone is brought 
to view in the Des Moines river about thirty miles below the 
city of Des Moines, itis quite evident that they lie at no great dis- 
tance beneath the surface. The Chester limestone so well develop- 
ed in some portions of the contiguous states is not represented 
in Iowa; and the coal measures of the state, as has been shown 
by White,* rest unconformably upon the St. Louis limestone. 
The stratigraphy at, and in the immediate vicinity of, the con- 
fluence of the Des Moines and Racoon rivers has recently been 
more clearly indicated than at any previous period, chiefly on 
account of numerous newl}^ made road and railway cuttings, 
and borings, though for the most part the records of the latter 
are, and will be for some time, inaccessible. 
The following are a few only of the sections examined: 
Section i. Railway Gutting N. E. N. W. 8, 18 N. 24 W. 
Feet. Ina. 
10. Soil 1 
9. Brownish yellow drift clay 3 
8. Clay shale (Carboniferous) 2 
jGeol. Iowa. II. 261. 
gCall, Am. Nat. XVI, p. 369; McGee & Call, Am. Jour.. Sci. XXIV. Sept . "82. 
JAm. Geologist, Vol. II, p. 2.'5. 
*Geol. Iowa, Vol. I, p. 225, et ser/. 
