V ALLEY 01< THE MISSISSIPPI. 45 



monly a thin bed of lignite ; dark, greyish clays still 

 follow, containing pyrites, and argillaceous iron ore, 

 often lying at the base of the cliffs in corroded, flat- 

 tcned, and rounded masses; and at the very lowest 

 level of the river, in low water, a second and much 

 thicker bed of lignite succeeds, exhibiting every gra- 

 dation from the state of wood, and also containing, 

 amidst more friable materials, indurated sand-stone 

 nodules, resembling those of argillaceous iron-ore, 

 containing impressions of the leaves of existing oaks* 

 as well as those of plants resembling species of Equi- 



selwn. 



We have to ascend the Arkansa 60 miles from its 



outlet, through the recent alluvium, before we arrive 

 at the commencement of the primitive soil. All the 

 inferior space intervening betwixt the Mississippi, 

 and White River, is so subject to inundation as to be 

 rendered totally uninhabitable. How far the sup- 

 posed ancient marine deposit extends into the Great 

 Prairie, which is about 90 miles in length, I have not 

 been able satisfactorily to ascertain, though from the 

 extent of adventitious gravel over the neighbouring 

 uplands, and the reappearance of its bed in the Pine- 

 bluffs, ISO miles above Arkansas, we have no reason 

 to suppose its termination short of the whole extent of 

 the prairie. Amongst the least equivocal marks of ma- 

 rine origin visible in this deposition, is the discovery 



# Such as those of Quercus phellos the Willow Oak and Q* 

 rubra or Q. coccinea the Red Oak. 



