E.W. Hilgard on the Tertiary formations, etc. 29 
Art. V.—On the Tertiary Formations of Mississippi and Alabam 
by Eue. W. Hinearp, Ph.D., State Geologist of sete 
tive age and characteristic fossils of three of the most important ° 
divisions ete been determined by the labors of Morton, Conrad, 
Lea, i], Tuomey and others. Most of these observations, how: 
ever, meee been confined tg a few localities, or to such as 
situated at short distances from each other in the direction of 
the strike, though sometimes affording complete sections in that 
It is my object in the present paper, to review the general re- 
sults of my own observations, as combined and collated with 
those of eich scientific observers to whose writings I have been 
able to refer. Ifin so doing Iam het to controvert the opinions: 
of some, it is in the interest t of scienc e, my opportunities for ob- 
— having afforded fuller data for reaching correct conclu- 
sions. No onecan appreciate more than I do, how much Amer- 
ican onalibe owes to the indefatigable research of Cones espe- 
cially. Had he been less active in promoting our systematic 
apis of the Tertiary, I iets have had fewer objections 
to offer to his opinions, and certainly fewer results to scie 
Among the sections best feteran to the study of the abuts 
Tertiary, ; are those afforded along the course of the Alabama and 
Tombigby rivers, by the we!l-known exposures of Claiborne and 
St. Stephens, where Sir Charles Lyell first definitively settled - 
the question of the age of the so-called Nummulite, more prop- 
erly Orbitoides, limestone; and observed the fact, ignored again 
y some su sequent writers on the subject, that the matrix of 
oui bones always lies below the true Orbitoides limestone. 
e Viekshurg and Jackson groups.—In most respects, the Clai- 
ine and the St. Stephens sections agree so closely, that their 
character was naturally considered as the type of the South west- 
ern Tertiary, until Conrad’s examination of the Vicksburg bluff 
showed the Orbitoides to be there associated with a fauna distinct 
from, yet equalling in variety and peculiarity, that of the Clai- 
borne sand. In view of the coincidence of leading fossils, never- 
theless, Conrad at once considered the part of ‘the Vicksburg 
gory first examined by him (No. 5 of Sec. 81, p. 141 of my 
iss. Report) as the near congener of the Orbincides limestone 
of St. Stephens. Yet he seems to have retained doubts as to the 
precise equivalence of the two divisions, which have lately found — 
expression in the separation attempted by him, of the bral eS 
marl and blue limestone from _ Orbitoides limestone 
