518 GEOLOGICAL HISTORY OF THE GULF OF MEXICO. 
and its bayous have mostly cut their channels into a clay forma- y 
tion foreign to the alluvium, from which some of the best soils of 
these bottoms are also directly derived; the alluvium being, on 
the whole, of little thickness. 
These clays form the lower division of the Port Hudson beds. 
The upper consists chiefly of yellow and whitish silts which at 
some points form a terrace along the edge of the bottom; while on 
the hilltops of the adjoining uplands lies the calcareous, silty 
loam (Loess), of the Bluff formation, differing from its equivalents 
farther north by the total absence of stratification, and the exclu- 
sive prevalence of terrestrial fossils. How this state of things was 
brought about, it is not easy to imagine, unless perhaps the tidal 
flow was instrumental therein. , 
Above the Loess we find usually a stratum of loam or bric 
clay, which near the larger rivers is sometimes 15-20 feet in thick- 
ness. It is devoid of stratified structure as well as of fossils, and i 
forms the sub-soil of most of the uplands of the Gulf States. 
The Terrace epoch has not left any marks in the way of beach 
lines or terraces distinctly referable, to that era. As regards 
the modern epoch, the Mississippi Delta presents the anomaly of 
progressing, not by simple alluvion, but through the singular 
agency of the Mudlumps, discussed in a paper lately published.* 
a E A 
- Col. CHARLES WHITTLESEY said he was gratified to find so many facts 
conspiring to sustain a theory of his own and a favorite theory of fifteen 
years standing, that the Quaternary of the Lower Mississippi is cotemp0- 
rary with the later epochs of the Northern Drift. 
He-thought it was now demonstrated that the bluff or Loess beds of the 
upper and lower Mississippi are identical. At the north there are in- 
stances of coarse transported materials overlying and underlying the 
Loe e blue, variegated, and red clays of the upper beds are closely 
allied in age with the Loess and are probably cotemporary with it and the 
Champlain clays. 
This Loess or bluff stratum extends from above the Falls of the Missis- 
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as it was gradually drawing to a close. Such a vast accumulation of ice 
and nevè, exceeding two thousand feet in thickness, required a long period 
for its dissolution, and in dissolving produced a vast fresh water sea, 
covering a country nearly flat, but having a drainage to the south. 
* Am. JoursSci,, March, April and May, 1871. 
