132 
IOWA ACADEMY OF SCIENCES. 
Henrietta, but it is not believed that it is everywhere the 
same continuous bed. At present, however, this median 
member of the Des Moines series furnishes about 7 per 
cent, of the total supply. The coal of the Henrietta division 
lies everywhere very near the base of the formation. 
Hence, if we should take a few feet of this terrane and add 
it to the Cherokee, we would have practically 98 per cent, 
of the entire Trans-Mississippian output of coal north of 
the Arkansas river coming from the lowermost member of 
the coal measures of this region — the Cherokee shales. 
It is a noteworthy fact that south of the Boston moun- 
tains the coal measures thicken enormously, and that the 
coal horizons, instead of being near the base of the section, 
are high above the Mississippian limestones. This is believed 
to be explainable by the fact that a very considerable part 
of the Arkansas and Indian Territory coal measures are by 
depositions unrepresented north of the southern boundary 
of Missouri. In the northern portion of the field the great 
erosion unconformity, which everywhere is found at the 
base of the Des Moines series, probably represents the time 
when, in the south, deposition was going on. This great 
sequence in Arkansas lying below the horizon of all the 
Cherokee, as displayed north of the Boston mountains, is 
perhaps sufficiently important to receive a taxonomic rank 
equivalent to the Des Moines or the Missourian. The exact 
upper limiting horizon of this great Arkansan series is not 
as yet determined. 
The thickness of the Cherokee shales may.be taken to be 
about 300 feet. From this measurement they taper out 
eastwardly to a feather edge. If the total thickness of the 
coal measures (Des Moines and Missourian series) north of 
Arkansas are taken at 2,000 feet, the basal one-seventh 
furnishes 98 per cent, of the whole output. 
NAMES OF COALS. 
Ardmorecoa! lower, Gordon. (Missouri Geol. Sur., Yol. IX, Sheet Kept. 
No. 2, p. 21, 1894.) In Macon county, Missouri, one of the lower coals of 
the Cherokee 
Beech coal, Marbut. (Missouri Geol. Sur., Yol. XII, pt. ii, p. 348, 1898.) 
In Howard county, MLsouri, a thin seam in the Henrietta division. 
BevDr coal, McGee. (Trans. St. Louis Acad. Sci., Yol. Y, p. 334, 1888.) 
