CARBONIFEROUS AGE. 321 



able. The average amount for the southern range is one hundred feet, and for the 

 middle and western, sixty feet each. 



In western Pennsylvania, where the coal is bituminous, the workable coal is confined 

 to the beds A to H of the section on page 311 ; and B, E, and H, or the Mammoth, Free- 

 port, and Pittsburg beds, are the largest and best. 



(c.) Interior-Continental Basin. — In Ohio, the Millstone-grit is in some places a coarse 

 conglomerate ; but it often rather abruptly thins out, or passes into sandstone. In Ar- 

 kansas, it is represented by a conglomerate 740 feet thick (Lesquereux). 



The thin limestones of the measures in Pennsylvania, Virginia, and Tennessee, 

 thicken somewhat as we go westward, form heavy beds in Indiana, Illinois, and west- 

 ern Kentucky, and occupy nearly the whole of the upper part of the section in Missouri 

 and Nebraska, where, on the contrary, the coal-beds are few and thin. Broadhead 

 states that the 1,900 feet of measures in Missouri contain 24| feet of coal. 



The following are regarded as the equivalents of the Mammoth and Pittsburg 

 beds : — 



(1.) Mammoth Bed (Second workable Pennsylvania bed). — The bed at Leonards, 

 above Kittanning, Pa. (3| feet thick), etc.; Mahoning Valley, Cuyahoga Falls, Chip- 

 pewa, etc , Ohio; the Kanawha Salines; the Breckenridge Cannel Coal and other mines 

 in Kentucky, the first (or second) Kentucky bed; the lower coal on the Wabash, Ind. ; 

 Morris, etc., 111. 



(2.) Pittsburg Bed (Eighth Pennsylvania bed). — Bed at Wheeling; at Athens, Ohio; 

 the Pomeroy bed, Ohio; at Mulford's, in Western Kentucky, the eleventh Kentucky bed. 



III. Life. 

 1. Plants. 



The abundance of Fossil Plants is the most striking characteristic 

 of the Coal era ; and the remains are so widely diffused, and are dis- 

 tributed through so great a thickness of rock and coal, that we may- 

 be sure that we have in them a good representation of the forest and 

 marsh as well as marine vegetation of the Carboniferous age. In 

 the marine, there is little peculiar to note. The land-plants, on the 

 contrary, reveal an expansion of some departments of the Vegetable 

 kingdom, which would not have been suspected were it not for the evi- 

 dence in the rocks. 



This terrestrial vegetation began, as already shown, in the Silurian, 

 and was well displayed before the close of the Devonian. The same 

 orders of plants were represented, but by more numerous species. 

 These orders, as stated on page 268, included the Acrogens, or higher 

 Cryptogams, and the Gymnosperms, or lower Phenogams. 



Of Acrogens, there were (1) Lycopods ; (2) Ferns; (3) Equiseta ; 

 and of Gymnosperms, the Conifers. To these, the Carboniferous 

 period adds the first known of Cycads, another tribe of Gymnos- 

 perms. 



Among the lower terrestrial Cryptogams, the remains of Mosses 

 have not been found ; but of Fungi or Mushrooms some evidence has 

 been obtained. There were no Angiosperms and no Palms. 



A general idea of the character of the vegetation, and also of the 

 21 



