THE MISSISSIPPI VALLEY. 327 



It is proper to remark, that tlie coal strata in that 

 part of the Alteghanies represented in our northern 

 section, are extensive and rise nearer to the summit of 

 the mountains than in the southern, though, in the de- 

 lineation, this and some other circumstances of minor 

 importance have heen omitted for the sake of simpli- 

 city. 



NORTHERN SECTION. 



The argillaceous sandstone, and the hlue horizon- 

 tal limestone, extend westward from the summit of 

 the Alleghany mountains to the Mississippi. These 

 are in immediate connexion, sometimes alternating 

 with each other, and often containing extensive heds 

 of coal accompanied hy strata of hituminous clay- 

 slate. They are the two most important mem- 

 bers of the great coal series of the valley of the 

 Mississippi. The sandstone is most frequent, and oc- 

 curs usually below the limestone ; towards the east it 

 passes into the inclined sandstone and wacke of the 

 Alleghany mountains. 



Near the Mississippi in longitude 13° W. from 

 Washington, is a remarkable stratum of yellowish 

 white or light gray sparry limestone, rather indistinct- 

 ly stratified, but disposed horizontally and containing 

 numerous organic relics. It is connected with the 

 carhoniferous sandstones, and sometimes passes into 

 the common compact blue lime stone. Associated 

 with it is an extensive stratum of an homogeneous si- 

 liceous rock resembling the petrosilex of some mi- 

 neralogists, and these two in the parallel of our north- 



