VALLEY OF THE MISSISSIPPI. 4?3 



Remarkable aggregation, appears, by a dip, to basset 

 out from beneath this calcareous platform, on the 

 northern banks of the river, near the entrance of the 

 Kiamesha. From its massive appearance, and ob- 

 scure greenish-grey color, it strongly resembled a 

 trap, or grauwacke; it proved, however to be a calca-t 

 reous sand -stone, with a crystaline cement) and like 

 the grauwacke, as well as sand, occasionally includes 

 adventitious pebbles, and angular debris, among 

 which we observed the existence of chalcedony. 



How far this calcareous formation extends into the 

 neighbouring province of Texas, and under what cir- 

 cumstances, I have not been able to ascertain ; but I 

 may further add, concerning its north-western limits, 

 that it appears to be essentially separated from the 

 older secondary calcareous formation, by the interpo- 

 sition of a transition range of mountains, stretching 

 towards the south-west, which separate the tributary 

 streams of the Arkansa from those which flow into 

 Red River ; and that from hence to the gulf of Mex- 

 ico in a south-east direction, traversing the plains of 

 Opelousas and Attakapa and the maritime part of 

 the province of Texas, no other chain of mountains 

 are known to exist. It is not necessary for us to trace 

 the maritime alluviumof the Atlantic states so well de- 

 fined in the essay of Mr. Maclure, and we shall now 

 merely add some remarks on its character as it ap- 

 pears in the valley of the Mississippi. Along the 

 immediate banks of this river, it is no where inter- 

 sected on its western border ; all the cliffs of reenter- 



