374 



PALEOZOIC TIME. 



of the contrast between the two regions may be gathered from a com- 

 parison of the section of the New York rocks, on p. 142, with the 

 general section of the formations in the Mississippi valley here pre- 

 sented. 



In the Lower Silurian of this section, the Calciferous beds are 

 mainly of limestone, as well as the Trenton and the greater part of 



Fig. 698. 

 Permian . . . 



Carboniferous 



SUBCARBONIFEROUS •{ 



fc ( Chemung . 

 9. I Hamilton . 



« ( CORNIFEROUS 



Niagara 



Cincinnati 

 Trenton 

 Canadian , 

 Potsdam . 



Permian. 



Coal-measures. 



Conglomerate. 

 Subcarboniferous limestone. 

 Subcarboniferous sandstone. 



Black shale (Huron). 



Cliff limestone. 



Blue limestone and shale. 



Trenton limestone; Galena limestone; 

 Black River limestone. 



Lower Magnesian limestone 

 Potsdam sandstone. 



Section of the Paleozoic rocks in the Mississippi basin. 



the Cincinnati Group. The Upper Silurian contains little but lime- 

 stone ; the Lower Devonian and the Subcarboniferous are also mainly 

 limestone. Moreover, many limestone beds intervene in the Coal meas- 

 ures ; and, west of the Mississippi, over a considerable portion of the 

 Rocky Mountain slope, the Carboniferous beds are mainly limestones. 

 The rocks of the northern border of the Interior Continental basin, 

 toward the Archaean, contain a much smaller proportion of limestone 

 than those of the central portion. 



The contrast between the Appalachian region and the Interior will become more ap- 

 parent from a few general sections. The first here given is from the State of Penn- 

 sylvania, which lies within the Appalachian region; it is from the Geological Report of 

 H. D. Rogers; the second is a section of the Ohio rocks, lying on the eastern border of 

 the Interior basin, from the Geological Reports of J. S. Newberry; the third is a sec- 

 tion of the Michigan rocks, lying on the northern side of the basin, by A. Winchell; 

 the fourth, of Iowa, which is also on the northern side, by C A. White ; the fifth and 

 sixth, of Illinois and Missouri, which are near its centre, — the former by A. H. 

 Worthen, the latter by G. C. Swallow, but with changes from more recent informa- 

 tion; the seventh, of Tennessee, of which the eastern part is in the Appalachian region, 

 and the middle and western in the Interior, by J. M. Safford. In each case, the 

 section begins below. 



