272 REPORT OF THE AMERICAN COMMITTEE. 
sands, with much glauconite, and characterized by the prevalence 
of shells of Ostrea Sellceformis. This is by far the most charac- 
teristic and persistent of the beds of the Claiborne formation. It 
extends certainly from Caldwell county in Texas, through Lou- 
isiana, Mississippi, Alabama, Georgia, and thence on to Mary- 
land. In places this part of the Claiborne division becomes 
highly ferruginous from preponderance of glauconite, giving rise 
to " red land " spots, and even to beds of iron ore, as near Duck 
Hill in Mississippi. According to Dr. Hilgard tiiis ferruginous 
feature increases to the westM'ard, until in Louisiana it makes a 
prominent one of the country and becomes geologically as well 
as practically an important mark. 
Above the Claiborne and forming our Upper Eocene, is the 
division which we have called the White Limestone, in places 
350 feet in thickness, though generally only about 200 feet. 
The White Limestone is subdivided into a lower part, 60 feet 
thick, consisting of impure argillaceous limestones, holding in 
many places, especially westward near the State line of Alabama 
and over the line in Mississippi, beds of gypsum and gypseous 
clays; a middle part, 200 feet thick, of rather pure white lime- 
stone containing, as a characteristic fossil, Orhitoides 3Iantelli; 
and an upper part, 150 feet thick, of white limestone containing 
large masses of silicified corals and a great number of plates and 
spines of echinoderras. In Mississippi, the uppermost beds of 
Marine Tertiary consist of alternating beds of Orbitoidal lime- 
stone and clays, some 100 feet or more thick, with about 60 feet 
of a lignitic clay at top. 
The lower sixty feet of the White Limestone are included in 
what Hilgard has called his Jackson formation. In this, and 
characteristic of the formation, are the remains of Zeuglodon 
Cetoides* 
The main mass of the White Limestone, its middle member, 
is the orbitoidal rock which, there is no reason to doubt, belongs 
to the Vicksburg division as defined in the Mississippi Surveys. 
The uppermost 150 feet of the White Limestone we have seen 
in one locality only; but there resting apparently conformably 
upon the orbitoidal rock. 
While the average Gulf-ward slope of the Tertiary formation 
* We have already given some reasons for placinjif this division along with 
the Claiborne. 
