E. W. Hilgard—Geological Reconnoissance of Louisiana. 389 
general section (p. 140 of the Mississippi Report of 1860). 
According to the observations of my companion, Dr. Walker 
(who determined the line between this and the Grand Gulf 
group, on the Washita), lumps of Orbitoides limestone at the 
foot of the Grand Gulf sandstone ridges, are the first evidence 
of the change of formation. Thence northward, lignito-gyp- 
seous clays are reported for some distance, while about six 
miles below Columbia, according to information from residents, 
— are limestone hills with small shell prairies and marl 
eds 
Northward of Columbia, calcareous strata corresponding to 
the Jackson group do not seem to occur on the Washita until 
we reach “about fifty miles (by water) south of Monroe,” 
the locality from which Dr. Harlan obtained the vertebre of 
Zeuglodon described by him in 1832.* Thus far, the section 
of the marine Tertiary on the Washita corresponds very we 
to that on Yazoo and Pearl rivers, in Mississippi; oniy the in- 
tervening lignitic stratum, which forms the base of the Vicks- 
bu bluff, is more extensively developed on the first mentioned 
eam. 
On the Sabine river, too, the vpper portion of the profile is 
pretty correctly reproduced. At the base of the Grand Gulf 
rocks we find, on the bayou Taureau, a seam of shell limestone 
with Vicksburg fossils. We then pass over lignito-gypseous 
Strata to Sabine Town, Texas, where we see about seventy feet 
of these, overlying ledges of blue fossiliferous limestone alter- 
nating every two or three feet with what would be greensand 
marl like that of Vicksburg, had not the lime of the numerous 
shells of which it contains casts, been removed by subsequent 
dissolution. So far as I have seen, the usual leading fossils of 
Vicksburg are wanting here ; while the greater sandiness of the 
Materials, as well as the prevalence of shallow-sea bivalves, in- 
dicates their deposition in shallower water. As we proceed 
northward from Sabine Town, lignitic clays and lignite alone 
Separate, and sometimes altogether replace, the limestone 
ges, which themselves become poorer in fossils, as we ap- 
proach the northern edge of the formation. 
yond, we again enter upon lignitic territory, which thence- 
forth continues with unbroken uniformity, so far as the Ter- 
is concerned, to the Arkansas line. 
* Trans. Am. Phil. Soc., vol. iv, N. 8. 
