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: 
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, 
C. A. White on the Geology of Southwestern Iowa. 25 
- of the material brought up, consists principally of bluish clayey 
shale. This boring was undertaken with the hope of finding a 
lower bed of coal, but was A upon reaching the lime- 
stone. A remarkable fact in relation to this section, is the exist- 
ence of the well defined border of the coal-field within two 
miles to the northeastward, where the Subcarboniferous lime- 
stone is seen well exposed. No satisfactory evidence of a dis- 
turbance of the strata cai be discovered in the vicinity, and the 
of the lowa river is the deepest point to which recent ero- 
sion has reached. 
rom these, and other similar facts collected along the border 
of the coal- field, it seems evident that the commencement of the 
Coal-measure epoch in Iowa found she then existing surface, 
ocal accumulation of sandstone strata similar to that in 
Hardin county are not uncommon in the lower Coal-measures: 
those sie at Red k in Marion county, and below Ottumwa 
Ilo county being of the same general character, and 
scobetie cotemporaneous deposits. These, and other i 
stratigraphical features in the series, will render its full elucida- 
tion a matter of some difficulty compared wi with similar labor in 
the upper series, which is composed to a ae extent Ms lime- 
stones, and its horizons consequently more definite and exten- 
ded. The lower series also, consisting as it does principally of 
friable sandstones and shales, presents comparatively few natu- 
exposures of its Age even where the drift material is | not 
ee much by way of preening = g Linologen contrast be- 
tween the upper and lower Coal-m s as herein designated. 
ae most legis section ead in ‘all that region comprisin 
sixteen counties before named, and perhaps the 
ne Fons one of the rocks of that age to be found in that 
state, was measured on the left valley-slope of Middle river, in 
the vicinity of Winterset, the county seat of county 
The strata of this section which are referred to t i 
reach a thickness of one hundred and eighty feet, - | are seen 
Am. Jour. S8c1.—Seconp Serres, Vou. XLIV, No. 130,—Juxy, 1867, 
4 
