150 
the tertiary geology of the 
and Gmnd G«lf rocks consist olmost throughout of hgnr. o-gyp^ous lam, nated clays, 
Ising upwards into more sandy materials ; they are not sensibly unconformable 
lee but while the Vicksburg rocks show at all long expos, .res a distinct southward 
L of some three to five degrees, the position of the Grand Gulf strata can ramly he 
shown to be otherwise than nearly or quite horizontal on the average; although in 
many cases faults or subsidences have caused them to dip, sometimes quite steeply, in 
almost any direction.”* , 
Towards the sea-coast, the lithological transition into the post-Pliocene is about 
equally well marked as the transition into the older deposits in the north. The most 
remarkable circumstance connected with the Grand Gulf deposits is the almost total 
absence of zoogene fossUs, whether land, marine or fresh-water. Up to 1881 it 
appears that only one solitary fragment of such fossil, determined to belong to 
a turtle, had been discovered ;t and even the plant remains are in most cases 
unrecognizable, although the general regularity of the strata, as well as their litho- 
logical character, would seem to indicate that they were laid down under most stable 
conditions, or such as would be most conducive toward animal or plant preservation. 
Whether the temporary seclusion or cutting off of the Gulf from the Atlantic, as has 
been premised by Ililgard, was a, or the primary cause in bringing about this 
anomalous condition, still remains to be proved, and it further remains to be proved 
that any such seclusion actually took place. 
Lonifiiana. 
The general features of the Tertiary formations of this State are very much like 
those of Mississippi, and call for no special consideration. Only three divisions of the 
scries, the Jackson, Vicksburg, and Grand Gulf, are officially recognized,! but it is 
not improbable that the Claiborne enters the northwest corner. 
The expo.sures of the Vicksburg beds occupy a belt 10-15 mUes or more § in 
width extending in a west— southwest direction from the Washita to the Siibine River. 
The distinctive fossUs of the group are sufficiently abundant, and we find, as in Missis- 
sippi, a frequent association of Orhitoides MantelU, Osfrea Vlckburgtnms, and Pteten 
I ouhom. Isorth of the ^ icksburg line to the Arkansas boundary the strata are largely 
of a lignitic character, anu indicate distinct alternations of marine and brack ish-water 
conditions. They are coUectively grouped under the Jackson period (“ Mansfield 
Group, in part, of Ililgard), a position seemingly indicated by the character of the 
fossd remains. The remains of Zeuglodo,, have been found at Montgomerv, in Grant 
parish, and at Grandview, on the Washita, a few mdes below Columbia. Of about 150 
apavioa of inveitebnikifo^aa collecte d fiom these deposits, it i, claimed that at leas, nine 
T A. J. Science, new ser., vol. ixii, p. 59. 
§ to mUet’S 
} augaro, A. J. Science, new. ser., vol. xlviii, p. 839, 1869. 
