48 
PROCEEDINGS OF THE ACADEMY OF 
Next in the descending order, we have formation F, which is two hundred 
and fifty to three hundred feet in thickness, and very similar, towards the up- 
per part, to the red bed D in its composition, excepting that it contains less 
gypsum; below, it passes into a very hard compact gray sandstone, the whole 
apparently destitute of fossils. 
It will, perhaps, be remembered we mentioned in one of our former papers the 
existence of some facts which we thought point to the conclusion that the great 
gypsum deposits of the south-west, might be on a parallel with No. 1, or the 
lower part of No. 2 of our Nebraska section. From the great similarity of these 
red formations near the Black Hills, to the red gypsum bearing deposits de- 
scribed by Mr. Marcou and others, in Texas, Arkansas, and New Mexico, we are 
now inclined to the opinion that they all hold the same position, and are of 
course much older than our No. 1. 
The entire absence, so far as we yet know, of organic remains in these red 
formations in the region of the Black Hills, as well as in the south-west, 
shows that during their deposition the physical conditions in the waters where 
they were deposited, must have been unfavorable to the existence of animal 
life. 
That the lower bed F, of the foregoing section, is of Carboniferous age, is 
very probable, coming in as it does immediately above a well-marked Carbonifer- 
ous formation, and below a limestone containing fossils closely similar to well- 
known coal measure forms, two of which belong to genera (^Bellerophon and 
Macrocheilm)^ not known, we believe, to range above the Carboniferous sys- 
tem. 
It is not, however, so easy to determine the age of the upper red bed D. From 
its stratigraphical position, as well as lithological characters, it might with 
almost as much propriety be referred to the Permian or Triassic systems, as to 
the Carboniferous. Yet as it appears to have been deposited during a repetition 
of the same physical conditions that prevailed during the deposition of the bed 
F, we think it is perhaps safer to refer it provisionally, in the absence of palaeon- 
tological evidence, to the Carboniferous system, though it is possible both these 
red beds and the intervening limestone may prove to be Permian. 
Immediately below the foregoing formations there is a rather fine grained 
somewhat gritty whitish subcrystalline limestone (G of the section), containing 
in great numbers a species of Spirifer, perhaps new, and resembling more nearly 
forms common in the lower Carboniferous series of the west than those of the coal 
measures ; along with this a fragment of another Spirifer was found, having fas- 
ciculate bifurcating costte, like S. Meiisehachanus (Rcemer), a common coal mea- 
sure fossil ; also two species of Produchts^ one of which is probably identical 
with P. semireticiilatuSj and an other similar, but smaller species, with apparently 
a less deeply marked sinus in the larger valve, and a shorter hinge. This bed 
passes gradually down into a yellowish gritty somewhat friable limestone, in 
which was found a Spirifer having a high area like S. cuspidaius ; and a large 
PJuomphalus, apparently identical with a species common in the Encrinital or 
Burlington limestone of the lower Carboniferous series in the west, — the two 
rocks are fifty feet in thickness. 
The succeeding formation is a hard yellowish gritty limestone often tinged 
with red (H of section), in which were found specimens of a small smooth Tere- 
bratula, a small deeply sinuate Productus, and a Syringopora ? having small, 
straight, very regularly disposed tubes, about -06 inch in diameter, and separated 
by spaces about -09 inch across. In the middle of this formation, which is 
usually forty feet in thickness, there is often seen an 8 foot layer of bluish rather 
compact argillaceous limestone, containing a smooth Terebralula resembling T. 
mbtileta (Hall), but perhaps distinct, and a Productus like P. cora^ in the fine- 
ness of its strisB. 
The fossils in the collection from these lower limestones (G- and H) are un- 
fortunately almost all in a very bad state of preservation ; so that it is nearly 
impossible to determine with any degree of certainty their specific characters. 
As near as can be ascertained, however, the majority of them appear to resemble 
[March, 
