344 Miscellaneous Notices in Opelousas, Attakapas, 6fc. 



Art. XV. — Miscellaneous Notices in Ojpelousas, Attakapas, ^c. ; 

 by Prof. W. M. Carpenter. 



Jackson, Lou., Nov. 8th, 1838. 



TO PROF. SILLIMAN. 



Dear Sir — I promised, some time since, to give you some- 

 thing on the prairie formation of the Opelousas and Attakapas 

 comitry ; but after an examination during two summers, I have 

 not been able to find much that is worth reporting. The 

 formation on which the prairies rest, is nearly the same as 

 that extending east of the Mississippi River, and across the 

 southern states to the Carolinas and Georgia. The age is evi- 

 dently the same, and the only apparent difference is in the color 

 of some of the layers, those on the east of the Mississippi being 

 derived from the Alleghany Mountains, and all those west of the 

 the river, having the deep ferruginous tinge peculiar to the sedi- 

 ment brought down from the Rocky Mountains, I observed lay- 

 ers of this kind as far west as the borders of Texas, wherever 

 wells were sunk to any depth. The superior layer, or that upon 

 which the prairies immediately rest, is a whitish clay containing 

 ferruginous gravel and rough calcareous concretions ; it is per- 

 fectly impermeable to water, and this may, in some degree, ac- 

 count for the absence of permanent vegetation ; the soil lying 

 upon this, being very thin and holding all the water during wet 

 spells, and on account of its small depth, drying very rapidly and 

 thoroughly under the influence of the sun, at other times, be- 

 comes subject to great extremes of saturation and drought. This 

 may be one reason why the vegetation of these prairies is almost 

 entirely of a transient nature ; thus, in wet seasons, those plants 

 are seen in abundance, which prefer wet localities, but these al- 

 ways disappear at the approach of drought. No plants are per- 

 manent except some hardy species of thorn trees, which bear 

 these extremes, and even these are stinted. The drought is 

 most injurious, for when a spot is shaded, trees grow to a large 

 size. On all these prairies there are ponds, which, on account of 

 the impervious natm'6 of the clay, contain water at all seasons. 

 They are often situated on the highest part of the prairie. They 

 are surrounded by the Zizania, Thalia dealbata, Cyperus articu- 

 latus, and many other marsh plants. These ponds seem to be 



