396 FE. W. Hilgard—Geological History of the Gulf of Mexico. 
water beds of the interior. And with these as fixed horizons 
to start from, aided also by the flora of the subordinate lignite 
beds of the later (Jackson and Vicksburg) stages, we may hope 
' to establish a comparative chronological scale through which 
the parallelisms with more distant regions, and later times, may 
be aw even for the much-discussed Tertiary beds of the 
est. 
My present purpose scarcely requires that I should more 
than allude to the detail of the later stages of the older Tertiary, 
which I have not distinguished on the general map, in order 
not to obscure too much the general features. Buta detailed 
map shows both the successive decrease in the width of their 
outcrops, and the regularly diminishing convexity of the Gulf- 
outline. I may also add that as we recede from the vertex of 
and more subordinate ; yet, by its persistent recurrence seem 
ing to intimate the occurrence, if not of oscillations, at least of 
local variations of depth; dependent, perhaps, upon corres: 
i outh A 
(much diminished) Vicksburg sea, here represented, appeats 
have intri ad al 
A 
the same time, let it be remembered that both east and west of 
the Mississippi, from the Chattahoochee to the Sabine, the older 
Te eriod closes with a decided prevalence, in the Vick# 
geological Feiss of the ulf does not exhibit any phenomen 
lie sesillel wi : cn the coast 
pproximation to, and admixture of, modern m# 
icksburg epoch closes abruptly, so far as the Gu : 
concerned, the marine Tertiary series. The geolo- 8 
