E. W. Hilgard on the Quaternary of Mississippi. 319 
tiver, the maximum thickness observed being about seventy-five 
feet. It is usually underlaid by some member of the Orange Sand, 
and this in its turn by the sandstones or clays of the Grand Gulf 
group (§ 236 et al.). The chief difference between the Loess of 
Mississippi and that of Indiana, is the greater fineness of the 
material, and the total absence, as far as observed, of any but 
terrestrial fossils. 
part from a few scattered sandgrains and calcareous con- 
cretions, it is a mouse-colored or buff, almost impalpable siliceous 
silt, but very lightly cemented by from 6 to 10 per cent of car- 
Onate of lime. Like the Loess of Kentucky, it contains, also, 
a large amount (5 to 7 per cent) of carbonate of magnesia. 
Helix, Helicina, Pupa and Achatina are the genera thus far 
found in it. As to the mammalian bones, they are here, as in 
Kentucky, found chiefly not in the usual material of the forma- 
tion, but in a “blue clay,” which, however, I have not thus far 
had an opportunity of examining in place. I should here state 
that the Mastodon bones mentioned by Tuomey as having been 
found in the “ Drift” of the lower Tombigby and Alabama, were 
y himself, upon reéxamination, referred to the Bluff, and not to 
the Drift or Orange Sand age. 
Above Vicksburg, the Loess deposits appear along the edge of 
the bluff, skirting the bottom, in irregular patches or narrow 
Strips, such as would be exhibited below Vicksburg, were the 
main body of the formation, riverward, to be cut away. Such 
undoubtedly has been the case here, for in Tennessee, according 
to Safford, it is again found regularly skirting the bottom, man 
miles in width. It seems also that, as we advance northward, 
the color and fineness of the material changes, so as to resemble 
more and more that comprising the Loess of Indiana and Ohio. 
No other river exhibits, within the state, any traces of the 
Loess along its course, so far as the latter is independent of the 
Mississippi river. The Big Black simply crosses the Loess re- 
gion; the Tallahatchie and Yazvo simply touch it by accident, 
as it were. Neither Pearl river nor the Pascagoula, show an 
Signs of it; while according to Tuomey, both the Tombigby an 
the Alabama river exhibit it characteristically, in the lower por- 
tion of their course. It would be interesting to study the cir- 
cumstances which determine this apparently capricious selection. 
From the predominant horizontality of the lines of contact be- 
tween the Orange Sand and Loess, it would seem that the depo- 
Sition of the latter was not preceded by any very extensive de- 
nudations into the surface of the former; the Loess thus indicat- 
ing, apparently, those channels which during the Drift period, 
formed the main outlets of its waters. 
The Yellow Loam.—Next in the upward order, and as distinct- 
ly superimposed upon the Loess where it exists, as it is else- 
