132 IOWA ACADEMY OF SCIENCES. 



Henrietta, but it is not believed that it is everywhere the 

 same continuous bed. At present, hov^ever, 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 v\diole output. 



NAMES OF COALS. 



Ardmorecoal, lower, Gordon. (Missouri Geol. Sur., Vol. 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., Vol. XII, pt. ii, p. 348, 1898.) 

 In Howard county, Mi-souri, a thin seam in the Henrietta division. 



BeviiF coal, McGee. (Trans. St. Louis Acad. Sci., Vol. V, p. 334, 1888.) 



