36 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



impure cannel. Worthen found many. They are from 150 feet to 

 2 or 3 miles in diameter, contain well-defined underclays with more 

 or less coal. In one, the coal dips to the center of the Httle basin; in 

 another, the coal thickens toward the center; in others, the coal is 

 irregular, but in all the coal thins out in approaching the border. 

 At one locality, marine limestone rests directly on the coal. Bain® 

 has discussed these localized deposits and has explained the concave 

 upper surface of the coal as due to consolidation of the vegetable 

 material. 



Similar small basins are numerous in Missouri, directly south 

 from Iowa, and occasionally they are of commercial importance. 

 Swallow^" says that some contain cannel, others, ordinary coal; but 

 the noteworthy feature is that in all the deposit is thick. In one he 

 saw 20 feet of good coal underlying 6 feet of cannel. Meek ex- 

 amined several in undisturbed Mississippian beds and others which 

 occupied hollows in Silurian limestones. Impure cannel is the pre- 

 vailing material but he saw good coal in one basin. Later observers 

 have gone more into detail. Potter^^ described a basin, only 200 

 yards in diameter, which yielded 22,000 tons of coal; it had two coal 

 beds, 2 and 16 feet thick. Another, 115 yards in diameter, yielded 

 3,730 tons ; its coal bed, with maximum thickness of 8 feet, thinned 

 away on the borders. One, examined by Winslow, occupies a hol- 

 low in the Magnesian (Lower Ordovician) and holds a coal bed, 

 almost 7 feet thick midway, and roofed with 7 inches of clay, on 

 which rests fossiliferous calcareous shale. More remarkable pockets 

 were described by Ball and Smith and were thought by them to 

 occupy " sink holes." In one case, the diameter is somewhat more 

 than 270 feet, while the depth is more than 130. Shale, 38 feet 



' H. F. Bain, Iowa Geol. Surv., Vol. VII., 1897, p. 300. 



" G. C. Swallow, First and Second Anm Reps. Geol. Surv. Missouri, 1855, 

 Part I., pp. 191-193; F. B. Meek, ibid., Part II., pp. 112-114; Reps. Geol. Surv. 

 Mo., 1855-1871, 1873, pp. 132, 149. 



" W. B. Potter, " Preliminary Report on Iron Ore and Coal Fields," Geol. 

 Surv. Mo., 1873, pp. 271-274; A. Winslow, " Preliminary Report on the Coal 

 Deposits of Missouri," 1891, pp. 168-171; S. W. Ball and A. F. Smith, "Geol- 

 ogy of Miller County," Bureau of Mines, Vol. I., 1903, pp. 100, 105, 107, 

 id8, III. 



