44 
PROCEEDINGS OF THE ACADEMY OF 
f D. — Brick-red, incoherent, argillo-calcareous, very fine slightly gritty 
I material, containing great quantities of gypsum in the form of 
I seams, layers, and irregular beds, — 100 to 150 ft. 
• I E. — Bluish and reddish gray, very hard gritty limestone, in which were 
a> I found a smooth spirifer-like S. lineatus, two or three species small 
J Pleurofomaria, two species Macrocheilus and one or two species 
M I of Bellerophon. This bed is variable in thickness, — 10 to 50 feei. 
3 I F. — Brick-red material, very similar to the bed D, excepting that it con- 
2 -{ tains much less gypsum ; passing down into a very hard compact 
concretionary sandstone, — 250 to 300 ft. 
G. — Hard, more or less gritty, yellowish and whitish limestone, contain- 
ing Productus, Spirifer, Uuomphalus, &c. &c., passing down into a 
light- yellow calcareous grit; altogether 50 ft, 
H. — Very hard reddish-gray limestone, containing Syringopora^ Producius. 
Terebratula, Ac. In the middle of this bed there is an 8 foot layer 
of very bard compact bluish limestone containing many crinoid re- 
mains, whole 50 ft. 
I. — Potsdam sandstone, containing Lingula^ Obolus ? and fragments of 
Trilobites, — 30 to 50 ft. 
J. — Highly metamorphosed strata, standing vertical. 
K. — Coarse feldspathic granite, forming mountain masses. 
The upper beds of the foregoing section, as seen along the Missouri, and in 
other portions of Nebraska, having been described on former occasions, and 
presenting few important new features, in the region of the Black Hills, we pass, 
for the present, at once to the consideration of those below, beginning with No. 
2. This formation, it will be observed, augments greatly in volume towards the 
west, its thickness along the Missouri, above the mouth of Big Sioux River, 
having been generally estimated at about ninety feet, while here, near the Black 
Hills, it attains a thickness of two hundred feet. As it appears to be en- 
tirely wanting on the Missouri, near Judith River above Fort Union, and is 
found to diminish rapidly as we ascend the Big Sioux from the Missouri ; while 
there are many facts pointing to the conclusion that it is one of the main fossil 
bearing beds of the Cretaceous series in Texas and New Mexico, we may rea- 
sonably infer that the sediment of which it is composed came originally from 
gome source fi\r to the southwest. 
Lithologically this formation presents much the same characters near the 
Black Hills as along the Missouri, being composed of dark gray laminated clays. 
Several of its characteristic fossils were also found near the S. E. base of tJie 
Black Hills amongst which we recognise Ammonites percarinatus (^UaW and Meek), of 
much larger size than those usually obtained along the Missouri, and numerous 
specimens of a Cijiherea, perhaps identical with C. tenuis (RnW and Meek). Some 
interesting new forms were likewise found associated with the foregoing, amongst 
which there is a large Ammonite, having septa somewhat like those of A. placenta, 
but rounded on the dorsum ; and a large strongly costated Ammonite, with very 
prominent nodes along the dorso-lateral margins, apparently very similar to a 
species described by Drs. Evans and Shumard under the name of J.. Galpinanus ; 
also a new species of Scaphites, closely related in the structure of its septa to 
^. hippocrepis of Dr. Kay. 
It will be remembered, we have in all our published papers, when speaking 
of that portion of the Nebraska section composing No. 1, expressed doubts re- 
specting its age. We placed it provisionally as the basis formation of the Cre- 
taceous series, but at the same time stated it was " not positively known to be- 
long to the Cretaceous system." In our last paper on the Nebraska formations, 
and their parallelism with those of the States, and the far southwest, communi- 
cated to the Academy in May, 1857, after having given all the facts in our pos- 
session bearing on this point, we stated that " although the weight of evidence 
