340 E. W. Hilgard—Geological Reconnoissance of Louisiana. 
Frem my own observations farther east, as well as from in- ’ 
formation obtained from others, it seems that there is a grad- 
ual increase of the lignitic clay facies in the Vicksburg sirata, 
as we advance westward from the Washita. The Casatche 
Hills below Natchitoches are described as consisting of alter- 
nating limestone and marl strata, capped by Orange Sand 
knolls ; while the ‘Grande Ecore” on Red river, a few miles 
above Natchitoches, exhibits only dark laminated clay and 
sand. In the flat region between Dugdemona and Red rivers, 
where I recrossed the Vicksburg territory, there is but little 
chance for observation ; but about the middle of the belt, on 
the heads of Bear creek, semi-indurate marls with Orbitoides, 
Pecten Poulsoni and Ostrea Vicksburgensis, are abundant ; as 
well as farther east, the nodular Orbitoides limestone, at the 
base of the Grand Gulf rocks. 
_ The Mansfield group.—tn Mississippi the stages of the ma- 
rine Tertiary are separated by lignitic clay strata ; in Alabama, 
on the contrary, they are directly superimposed upon each 
other.* The lignitic bands gradually increase in thickness as 
we advance westward, but the territory underlaid by them in 
Mississippi is generally too limited, and the development of 
the strata too slight, to necessitate their designation by a spe- 
cial name. At Vicksburg, nevertheless, the thickness of the 
lignitiferous stratum intervening between the Vicksburg and 
ackson groups, is not less than 35 to 40 feet, and it underlies a 
district several miles in width, on the Yazoo bluff. 
In western Louisiana, as already stated, none but lignitife- 
rous strata of Tertiary age, occur north of the Vicksburg group, 
as far north as Shreveport, and so far as I have been able. 
ascertain, up to the Arkansas line. In fact, the only locality 
ady mentioned as the source of Zeuglodon bones, described 
by Dr, Harlan, about half way between Columbia and Monroe, 
on the Washi 1 
Tertiary epoch seems to be, in both states, represented by hig 
* This’Journal, Jan., 1867, p. 30. 
+ Prelim. Report on the Texas Geol. Survey, 1866, p. 44. 
