38388 EF. W. Milgard—Geological Reconnoissance of Louisiana. 
consists of the gnarled and knotted concretions characterizing 
the Bluff formation (“Loess-puppets”), which contain the He- 
lices usual in that group. Faint and usually irrecognizable im- 
pressions of leaves sometimes occur, as is the case in Missis- 
sippi; but in the present condition of phyto-paleontology, 
little can be hoped for from that slender source. In its strati- 
graphical, lithological and structural characters, it differs widely 
from all the other tertiary deposits of the Southwest ; its 
slight dip alone proving it to be of comparatively modern ori- 
gin. hatever may be the precise epoch of its formation, that 
event could not have been a local one, due only to a littoral 
shallowing of the Gulf. The regularity, as well as the uni- 
formity of composition of the strata, from the Escambia river 
to the Colorado of Texas, alone seems to forbid its being con- 
sidered, like the Port Hudson deposits, as the representative of 
a period of swamp and estuarian formations on the border of a 
marine basin. I have heretofore suggested,* that nothing short 
of a temporary cutting off of the Mexican gulf from the At- 
lantic seems capable of accounting for the existence of the 
Grand Gulf strata ; and this impression has been nowise weak- 
ened by a more extended acquaintance with this remarkable 
formation. 
While the territory of the Grand Gulf group is on the whole 
perhaps the least fertile portion of Louisiana, (as is likewise 
the case in Mississippi), there are some notable exceptions to 
this rule, in regions where a calcareous clay stratumt comes s0 
near the surface as to contribute to the formation of the soil on 
the hillsides and in the bottoms. Such is the case on the up- 
per bayou Anacoco (in the “ Anacoco prairie” region) as well 
as in the southern portion of Sicily Island, near Harrisonburg 
on the Washita. Whether the Avoyelles prairie belongs to 
the same cajegory, I have been unable to ascertain ; but from 
its pouton it seems likely tha‘ such is the case. : 
his white clay marl, the building stones occurring in the 
northern portion of the formation, the potter’s clays above Te- 
ferred to, and a pure white and exceedingly refractory, semi-In- 
durate white pipe-clay, occurring near the edge of the Vi 
burg rocks in Catahoula parish, constitute the practically use- 
ful materials of this group in Louisiana ; where on the whole, 
it yields much fewer waters impregnated with noxious salts, 
an is the case in Mississippi.t : 
The Vicksburg group.—The territory underlaid by the rocks 
This J 
Probabl ya gat Ss oe te weten Oo MS 
at Samos hte Diu) and has boc kced aoa Trae (Anisp BPO 
. Toi, p. hoe et al. 
