214 T. A. Conrad on the Hocene Formation, §c. 
have their roots in the summit line of the fossiliferous loam; 
eight feet beneath the surface of the hills. These are the kinds 
of trees which first take possession of the soil made by deposition 
from the Mississippi near its mouths, and which refuse to grow 
on the hills above the loam or in the earth which overlies it. 
These trees grow only on the summit line of the loam, follow- 
ing all its undulations, and many are of such a size that they are 
evidently nearly as old as the excavations which have given them 
a chance to spring. up. ©The railroad has been made about ten 
years, and Dr. Bryan assures me that the trees made their appear-_ 
ance soon after the hills were cut through. The seeds or roots 
must therefore have been in the newest deposits of loam, and it 
is evident that no vegetation, except canes or reeds, occupied the 
soil before its latest deposition, at which latter period it is probable 
that the willow, cottonwood, and other trees, first made their 
appearance on the earth, and perhaps the mastodon, elephant, hip- 
popotamus, é&c., came into existence at the same time, since the 
remains of the mastodon and elephant have been abundantly 
found in the vicinity: of Natchez and Vicksburg, though I have 
not ascertained in what part of the stratum they occur. The 
foregoing facts and observations have led to the inference that all 
this thick and elevated deposit, with land universally distributed 
through it, was the result of ancient floods in the Mississippi and 
its tributaries.. The cause, whatever it may have been, which 
elevated the Eocene strata of the Mississippi bluffs, raised at the 
same time this ancient alluvium, and thus the uprise of the ter- 
tiary may be referred. to a very modern period, and one which 
seems to have been connected with the causes which destroyed the 
mastodon, elephant, hippopotamus, &c. which once existed in North 
Amenca. It is difficult to account for the origin of the peculiat 
earth above the fossiliferous loam, or to assign a cause for the un- 
dulations of the surface of the latter, which conforms to the slopes 
of the innumerable hills in this country, where there is no level 
ground except that subject to floods from the rivers. — It is certain, 
however, that the lakes are numerous, their shores steep and high, 
and that a future elevation of the country would present a large 
proportion of steep declivities, having their origin in the present 
sloping shores of the cut-off lakes which are common near all 
the rivers, where they approach the Mississippi. 
There Seems to be no other theory than the one I have sug- 
stec ‘which can account for the origin of the fossiliferous loam. 
