PALEOZOIC TIME — CARBONIC. 647 



limestone, Spirifer glaber var. contractus M. & W., 1009, Spiriferina spinosa ; 1012, Chonetes 

 llUnoisensis W., Productus parvus M. & W. 



(c) Lamellibranchs. — Kinderhook 1. : Cardiopsis radiata M. & W. Burlington 1. : 

 Aviculopecten Burlingtonensis M. & W., Iowa. Keokuk 1. : Aviculopecten Ovjeni, A. ohlon- 

 gus, A. aniplus, of M. & W., 111. St. Louis 1. : Myalina concentrica M. &. W., Nucula 

 Shumardana H., Warsaw, Idaho, N. nasuta H., ibid., Conocardium Bleekanum H., ibid. 

 Chester 1. : Pinna Missouriensis Swallow, 111., Myalina angulata M. & W., 111., Schizodus 

 Chesterensis M. & W., 111. 



(d) Gastropods. — Kinderhook 1. : Straparollus lens H., Goniatite bed, Ind., Bellero- 

 jihon cyrtolites H., ibid. Burlington 1. : Platyceras reversum H., Iowa. Keokuk 1. : 

 Pleurotomaria Shumardi M. & W. , 111., Platyceras equilaterale H., Iowa. St. Louis 1. : 

 Dentalium venustum M. & W., 111., Straparollus similis M. & W., Spergen Hill, Ind., 

 ^S". Spergensis H., ibid. 



6. Vertebrates. — Fishes. — The species of American Subcarboniferous Fishes have 

 been described mainly by Newberry, Newberry and Worthen, and St. John and Worthen 

 in the Ohio and Illinois Geol. Keports. The species described by Newberry and Worthen, 

 from Illinois specimens, include 16 of Hybodonts, 26 of Petalodonts, 52 of Cestracionts, 

 with 9 of fin-spines and Psammodonts. St. John and Worthen have added over 50 .species 

 of Cochliodonts, a dozen of Psammodonts, and over 20 kinds of fin-spines {III. Geol. Pep., 

 vol. vii., 1883). Fig. 1018, tooth of Cochliodus noUlis N. & W., 111. ; 1021, Gladodus 

 spinosus N. & W. , St. Louis 1., Mo. ; a, section of the same ; 1020, Garcharop>sis Wortheni 

 Newb. , Huntsville, Ala.; 1022, Orodus mammillaris N. & W., Warsaw, 111. The Subcarbo- 

 niferous at Ogden has afforded a tooth of a species of Dendrodus. 



2. CarbonifepvOUS Period. 



Since the Carboniferous period, or that of the Coal-measures, was a period 

 largely of marshes, as it opened the land gradually became emerged; and the 

 first rocks that were laid down bear evidence, in many regions, of the change 

 of condition by their beach-like character. Other evidence of the transition 

 epoch exists in erosions over the Subcarboniferous rocks, making a surface 

 of hills and depressions for the reception of the later depositions. Part of 

 this irregularity may be the work of denudation before the Subcarboniferous 

 period had closed ; but other parts are referred to the time of emergence. 



ROCKS — SUBDIVISIONS, KINDS, AND DISTRIBUTION. 



The most prominent subdivisions of the Carboniferous formations are 

 those of (1) the Millstone grit, or the Great conglomerate, named, in Penn- 

 sylvania, the PoTTSviLLE Conglomerate; and (2) the Coal-measures. 



THE POTTSVILLE CONGLOMERATE. 



The conglomerate beneath the coal-measures is generally a hard gritty 

 siliceous rock, made of quartzose gravel or sand — a rock that was literally 

 a millstone grit early in the century. It has a thickness of 800 to 1700 feet 

 in the center of the Anthracite region of Pennsylvania, but thins northward 

 in this state to less than 300 feet in the Wilkesbarre region, and westward to 

 200-300 feet. Its lower part spreads northward into western Kew York and 

 constitutes there the " Olean conglomerate " of Alleghany and Cattaraugus 

 counties, the rock of " Eock City," 25 to 60 feet thick. It extends westward 



