46 GEOLOGICAL STRUCTURE OF THE 



of shells, which accidentally came to my notice a few 

 miles below the Pine-Muffs, picked up by the chil- 

 dren of some of the French hunters resident in this 

 country, and consisting of a species of ostrea, like 

 that of the Santee, penetrated by seams of calcareous 

 crystals, exhibiting marks of a former attachment to 

 a softish ferruginous sand-stone, and containing frag- 

 ments of lignite. On the same sand-bar was also 

 found a small conch-shell,* which did not appear to 

 have been imbedded. 



This massive deposit, in all probability, makes an 

 appearance at Alexandria on Red River, to which 

 place the recent alluvium also extends ; aud the fer- 

 ruginous conglomerate resembling that of New Jer- 

 sey we have found to continue more than 1000 miles 

 up this river. From a consideration of these circum- 

 stances, and the direction of the t transition chain of 

 mountains, which traverse this territory nearly from 

 north-east to south-west, we are led to suppose the ex- 

 istence of the more recent calcareous platform nearly 

 to the sources of Red River, where it is probably suc- 

 ceeded by the gypseous red clay and salt formation. 



The extraordinary breadth of that part of the al- 

 luvial valley of the Mississippi, subject to inundation, 

 from the mouth of the Ohio to the ocean, said to be 

 of the extent of from 30 to 40 miles, is easily account- 

 ed for, in the friable nature, and the magnitude of the 

 marigenous deposit through which it flows. Its bed 



* Strombus pugilis. 



