46 
GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI., 
low depth, but often extend over large areas. The ferruginous sandstone is always formed 
immediately above a bed of clay or some material which checks the downward flow of 
water. The water passing through the Lafayette takes up iron oxide in solution, and being 
checked by the underlying impervious bed deposits the iron oxide, thus cementing the 
sands into a compact mass. This mass is constantly increased by the addition of more 
iron from the iron-charged waters. Gradually the overlying material is carried away until 
the ferruginous sandstone is reached; this resists the action of erosion and forms a scarp on 
the tops and sides of many hills. 
Where the Lafayette is thick it is the source of a very desirable and easily accessible 
supply of potable water. The great amount of sand in the formation forms a natural filter 
for the water. Many of the springs and the shallow wells of the State derive their water 
from the Lafayette. 
PORT HUDSON FORMATION. 
In the American Journal of Science, volume 47, 1869, page 79, Doctor Hilgard first 
described the Port Hudson formation at the type locality, Port Hudson, Miss. The fol- 
lowing sections were made by him along the river near the town : 
Sections of Port Hudson formation near Port Hudson. 
Near sawmill, Port Hudson. 
Midway between Port Hudson and Fontania. 
No. 
Material. 
Thick- 
ness. 
Material. 
Thick- 
ness. 
6 
Feet. 
4-6 
25 
Feet. 
8-10 
White and yellow hard pan 
18 
Orange and yellow sand, sometimes fer- 
ruginous sandstone, irregularly strati- 
fied . 
8-15 
4 
7 
3 
2 
1 
Gravel, sand, and clay in irregular 
bands, like river alluvium; with 
pebbles, driftwood, leaves, and 
mastodon bones. 
Heavy greenish or bluish massy clay, 
similar to No. 4. 
6 
25 
White indurated silt or hardpan 
Heavy green clay, with porous calcareous 
concretions above, ferruginous ones be- 
low; some sticks and impressions of 
leaves. 
Brown muck and white or blue clay, with 
cypress stumps. 
18 
30 
3-4 
At the stage of extreme low water [says Hilgard] prevailing at the time, the stump stratum (No. 1) 
was visible to the thickness of 10 feet at its highest point, showing several generations of stumps above 
one another, also the remnants of many successive falls of leaves and overflows. The wood is in a good 
state of preservation; no prostrate trunks are to be seen at present. 
The main clay deposit (No. 2) varies but little in general character; although very solid, its tendency 
to cleave into prismatic forms renders it very liable to "cave "into the river. The upper portion of the 
stratum, especially near its southern end, contains strings of calcareous nodules, on stratification lines 
8 to 12 inches apart. No fossils save rare impressions of leaves. 
No. 3 is exceedingly variable. At the northern end of the outcrop it is a narrow band of swamp 
deposit; at the first of the profiles given it bears the character of a sandbar; lower down it returns to 
that of a swamp deposit; still below it is represented by a fine white silt, without a trace of vegetable 
remains. Lower down again a lignitic layer appears at its base, with leaves and fruit of living species 
of lowland trees; while near Fontania it is again a sandbar, with an abundance of prostrate trunks of 
driftwood, coarse sand, and pebbles. 
The green clay stratum (No. 4) varies little, either in thickness or composition, and, like the stump 
stratum (No. 1), forms a convenient level of reference. 
The hardpan (No. 5) 1 conceive to be the more immediate representative of the loess proper, with 
which it is connected by gradual transition, though at times greatly resembling some of the materials 
of the Lafayette. It is void of fossils. 
