* 
344 Miscellaneous Notices in Opelousas, Attakapas, §c. 
Arr. XY. ae Notices in Opelousas, Attakapas, ee; 
of. W. M. Carpenter. 
: Jackson, Lou., Nov. 8th, 1838. 
To PROF. SILLIMAN. 
aah Sir—I dna some time since, to give you some- 
thing on the prairie formation of the Opelousas and Attakapas 
‘country ; 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. 1 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 walcayeous 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 refer 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 nature 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 artict- 
latus, and many other marsh plants. These ponds seem to be 
