3 5 OR Ok mae 113 
The Oriskany Sandstone of Missouri is a light-gray dimestone, 
which contains the Spirifer arenosa, Leptaena depressa, and several 
new species of Spirifer, Chonetes, Illenus and Lichos. 
The Devonian rocks occupy a small area in Marion, Ralls, Pike, 
Callaway, Saline and Ste. Genevieve Counties. 
SYSTEM VI—SILURIAN. 
Of the Upper Silurian series, we have the following formations: 
LowER HELDERBERG, 350 feet; Nracara Group, 175 feet ; 
Cape GIRARDEAU LIMESTONE, 60 feet. 
The Lower Helderberg Group is made up of buff, gray and 
reddish, cherty, and argillaceous limestones, blue shales, and dark 
graptolite slates, Dalmania tridentifera, Chierurus Missouriensis, 
Calymene rugosa, Orthis hybrida, O. elegantula, and several spe- 
cies of Platyostoma, are the prevailing fossils. 
Niagara Group.* The upper part of this formation consists of 
red, yellow, and ash colored shales, with compact limestones, varie- 
gated with bands and nodules of chert. 
Halysites catenularia, Columnaria inequalis, Calymene Blumen- 
bachit, and Caryocrinus ornatus, are the most characteristic fos- 
sils. 
Cape Girardeau Limestone. 1 am also indebted to Dr. SHuMARD 
for a description of this formation. 
According to him, ‘It is a compact, bluish-gray, brittle lime- 
stone, with a smooth fracture, in layers from two to six inches in 
thickness, with thin argillaceous partings. 
‘¢ These strata contain a great many fossils, principally Trilobites 
and Crinoides. In a small slab, not more than three by three 
inches, I have counted four genera of Trilobites, namely: Cyphas- 
pis, Girardeauensis, Acidaspis Halli, Proteus depressus, Asaphus, 
Nov. Sp. None of the Trilobites have been before mentioned in 
this country, and, so far as I can ascertain, the species are distinct 
from European forms. According to BARANDE, the first three 
genera occur in the greatest number in the Upper Silurian period, 
and are very sparingly represented in the Lower Silurian groups, 
The Crinoids belong mostly to the genera Glyptocrinus, Homocri- 
nus, Tentaculites, and Palzaster ; and the shells to Leptaena, Or- 
this and Turbo—all being of undescribed species. 
‘‘ These strata occur on the Mississippi River, about one mile 
and a half above Cape Girardeau, Thickness, forty to fifty feet. 
LOWER SILURIAN, 
We have thus far observed ten formations belonging to this 
series : 
Hupson RIver Group, 220 feet ; TRENTON LIMESTONE, 360 feet; 
BLack RIVER AND BIRDS-EYE LIMESTONE, 75 feet; 18ST MAGNESIAN 
LIMESTONE, 200 feet ; SACCHAROIDAL SANDSTONE, 125 feet; 2ND 
MAGNESIAN LIMESTONE, 230 feet; 2ND SANDSTONE, 115 feet; 3RD 
_MaGNESIAN LIMESTONE, 350 feet; 3RD SANDSTONE, 60 feet; 4TH 
. MAGNESIAN LIMESTONE, 300 feet. 
2 
* I am indebted to Dr. SHUMARD for the information possessed respecting the 
Niagara and Lower Helderberg Groups, and the Oriskany Sandstone, as I have 
not examined those formations very carefull. 
HUDSON RIVER GROUP. 
There are three formations, which we have referred to this group. 
ist. Immediately below the Oolite of the Onondaga limestone, 
in the bluffs both above and below Louisiana, we find some forty 
feet of blue, gray and brown, argillaceous, magnesian limestone. 
The upper part of these shales is in thick beds, presenting a dull, 
conchoidal fracture, and containing Asaphus megistos, and Caly- 
mene senaria. 
The lower part of this division becomes more argillaceous, and 
has several thin beds of bluish-gray, crystalline limestone, intercal- 
ated, which contain many fossils of the following species: Zep- 
taena sericea, L. alternata, L. planumbona, Orthis jugosa, O, sub- 
guadrata, and Rhynconnella capax. 
There are, also, strata of calcareo-arenaceous slate, in the same 
position, filled with remains, which I am unable to distinguish 
from Prof. HaL.’s Paleophycus virgatus, and another contorted spe- 
cies. There are, also, beds of slate, similar to those above men- 
tioned, at the base of these shales, whose surfaces are covered with 
great numbers of the Linguda ancyloidea. 
2d. On the Grassy, three and a-half miles northwest of Lou- 
isiana, about sixty feet of blue and purple shales are exposed 
below the beds above described. They contain three species 
of Lingula: Lingula quadrata, L. fragilis, and still another, not 
named. ;' 
3d. Under the 2d division are some twenty feet of argillo-mag- 
nesian limestone, similar to that in the 1st division, interstratified 
with blue shales. Orthis subguadrata, O. jugosa, Leptena alter- 
nata, Rhynconnella capax, and Asaphus megistos are abundant. 
These rocks crop out in Ralls, Pike, Cape Girardeau and Ste. 
Genevieve Counties. On the Grassy, a thickness of one hundred 
and twenty feet is exposed; and they extend below the surface to 
an unknown depth. 
TRENTON LIMESTONE. 
The upper part of this formation is made up of thick beds of 
hard, compact, bluish-gray and drab limestone, variegated with 
_ irregular cavities, filled with greenish materials; while the beds 
below are filled with irregular cylindrical portions, which readily 
decompose on exposure, and leave the rocks perforated with 
numerous irregular passages that somewhat resemble those made in 
timber by the Zoredo navaiis. The appearance of the rock, when 
thus decomposed, is very singular, and is a well marked character 
of this part of the formation. The decomposed, honey-combed 
portions are most admirably adapted to ornamental rock work. 
These beds are exposed on the plank road, from Hannibal to New 
London, north of Salt River, and near Glencoe, St. Louis County, 
and are seventy-five feet thick. Below them are thick strata of 
impure, coarse, gray and buff, crystalline, magnesian limestone, 
with many brown, earthy portions, which rapidly disintegrate on 
exposure to atmospheric influences. This part may be seen in the 
bluff of Salt River, near the plank road, 150 feet thick. The lower 
part is made up of hard, blue and bluish gray, semi-compact, 
silico-magnesian limestone, interstratified with light buff and drab, 
soft and earthy magnesian beds. Fifty feet of these strata crop out 
at the quarries south of the plank road bridge over Salt River, and 
on Spencer’s Creek in Rall’s County. The middle beds sometimes 
