GEOLOGY. 215 



as well as other species ; and they are all mineralized into 

 red chalcedony. 



" The upper strata of this Gabouri limestone present a 

 beautiful rock with an oolitic structure, which is now quarried 

 for architectural purposes. It is doubtless an equivalent of 

 that which occurs in the Burlington group, Iowa. It extends 

 itself to the right and to the left of the Missisippi, to near the 

 Ohio river, and even through Kentucky and Tennessee. The 

 fossils contained in the oolitic limestone of the Gabouri are 

 obscure and undeterminable ; but, in other localities, this 

 rock has yielded pentremites pyriformis, pentremites globo- 

 sus, pentremites florealis, that have been described by Say, 

 and a fourth species, which is new. 



" I have deemed the foregoing digression necessary in 

 order to connect the geology of the country just described, 

 with a more recent formation, previously alluded to, with 

 which I am to meet in ascending the Missouri. 



" I landed a mile or so before reaching the mouth of the 

 Sioux River, on the left bank of the Missouri, to examine a 

 rocky bank, seemingly a continuation of those apparent at 

 Wood's Hill. I found it to consist of — 



" 1st. A carboniferous limestone ; 



'' 2d. An argillaceous schistose limestone. 



" The rocks in this locality reach only to an elevation of 

 seven or eight feet above the level of the river ; and I take 

 notice of them here, because I am disposed to think that the}^ 

 are the last representatives of the carboniferous series in the 

 ascent of the Missouri, and that the mouth of the Sioux 

 River is the true limit in this direction of the old fossiliferous 

 rocks. 



" The rocks of which it (Dixon's Bluff ) is composed, are 

 the same that constantly make their appearance on ascending 

 the river, at the base of the hills which bound the valley. I 



