PENNSYLVANIAN. 467 



clays. These rocks may have had an original extent equal to or greater than the underlying 

 sandstones. 



Above the rocks just described are about 300 feet of rocks approximately corresponding 

 in age with the Allegheny formation of Pennsylvania. These rocks are predominantly shaly. 

 They contain at least sixteen coal beds, several of which are widely workable, forming the pro- 

 ductive part of the Pennsylvanian. The coals are usually underlain by clays and overlain by 

 shales. Most of the shales are either light colored and contain fragments of land plants or a 

 marine or brackish-water fauna, or they are black and highly bituminous and contam an open- 

 sea fauna. As a rule marine limestones closely overlie the roof shales, and at several horizons 

 such limestones underlie the underclays. The beds of this part of the section are very persistent, 

 many coal beds, clays, and limestones having been traced more or less continuously over large 

 parts of the field. The geology of the basin has been described in several State and Federal 

 reports." 



The coals have been variously designated by numbers and letters. In Illinois the coals 

 of this part of the series have been called Nos. 2 to 7. In Indiana they are known as coals 

 II to VII, some of which correspond to coals of similar number in Illinois, and for the smaUer 

 intermediate coals small letters have been added. Numerals also have been used in Kentucky, 

 where 9, 11, and 12 correspond to V, VI, and VII of Indiana and Illinois.*"' ^'"' "^^ 



The upper 1 ,000 feet of the series is characterized by more limestones, some of them widely 

 persistent, by thinner and fewer coals, and by more sandstone. 



In the early reports the Pennsylvanian of this basin was divided into (1) Basal sandstone or 

 Millstone grit, (2) Lower or Productive Coal Measures, and (3) Upper or Barren Coal Measures,'" 

 the line between the "Upper Coal Measures" and the "Lower Coal Measures" being drawn at a 

 limestone variously known in the reports of different regions as the Shoal Creek, Curlew, Car- 

 thage (?), Carlin villa, New Haven, and Somerville limestone, local names being also given to 

 some of the other more persistent limestones and sandstones of the coal measures. In 1898 the 

 present writer '° divided the coal measures of Indiana into "divisions " on the basis of the prin- 

 , cipal coals, an arrangement continued in his supplemental revised report published in 1909.*° 

 The sandstone of PottsvUle age in Indiana had previously been designated the Mansfield sand- 

 stone by Hopkins.*"^ In 1900 the series was divided by the writer ^' into the Mansfield, 

 Wabash, and Merom groups, corresponding respectively to (1) the Mansfield sandstone and 

 associated rocks; (2) the rocks between the nonconformities above the Mansfield sandstone 

 and below the Merom sandstone; and (3) the !Merom sandstone and overlying rocks. In 1902 

 and 1903, for cartographic purposes. Fuller and Ashley^*'- ^" divided the series above coal VII 

 into the Wabash, Inglefield, Ditney, Somerville, and Millersburg formations, and the upper 

 part of the series, below coal VII, into the Petersburg and Brazil formations. 



In view of the probable difficulty of carrying the bounding lines of these formations over 

 all the basin, the names have not been retained in recent work. Since 1906 White and Weller 

 have done considerable paleontologic work in all parts of the basin, in addition to the strati- 

 graphic work in Illinois by DeWolf and in Indiana by the writer. (See references above.) As 

 a result, the Pennsylvanian of the eastern interior basin has been divided into three formations, 

 the first, or Pottsville, extending from the bottom of the series up to the top of the underclay 

 of coal II in Indiana and coal No. 2 in Illinois; the second, or Carbondale formation, extend- 

 ing from that horizon up to and including coal No. 6; and the third, or McLeansboro forma- 

 tion, from the top of coal No. 6 to the top of the series. It is possible that future work may 

 show that the limestone which in the Illinois State reports has been called Shoal Creek lime- 

 stone can be traced over all of the basin, and that it may again be used as a line of division 

 between the upper and lower parts of the McLeansboro formation. Coal V of Indiana, which 

 appears to be the same as coal No. 5 of Illinois and coal 9 of Kentucky, may be developed 

 throughout most of the coal field. If future tracing shows that it is, it may possibly be used 



<2 Illinois State Geol. Survey, vols. 1-7, 1866-1890; Bulls. 3, 4, 6, 8, 1906. Indiana Dept. Geol. and Nat. Hist., 

 vols. 1-14; vol. 23, pp. 1-1573, containing a detailed report; vol. 33, containing a revised supplement to the report in 

 vol. 23. Kentucky Geol. Survey, vols. 1^; vols. 1-5, new series; reprints A, C, D; Bulls. 3, 4. U. S. Geol. Survey, 

 folios 67, 84, 105, Geol. Atlas TJ. S.; Twenty-second Ann. Rept., pt. 3, 1902, pp. 272-303. 



