118 GEOLOGY. 
Specimens in the beautiful collections of Dr. Hayden, which I have been kindly permitted to 
examine, exhibit these different phases of growth more distinctly than do mine, and show the 
species to have attained a large size. 
Locality and formation.—The specimens of A. percarinatus, which are in my collection, are 
possessed of no ordinary interest, as they afford the best of evidence as to the age of a series of 
strata which have been subjects of considerable difference of opinion. I obtained them from 
bands of limestone traversing the green shales, underlying and interstratified with the yellow 
sandstones which overlie the variegated marls, red and white calcareous sandstones, and 
gypsum, called by D’Shumard the ‘‘Gypsum formation.’? By Mr. Marcou the series of varie- 
gated marls is regarded as Triassic, and the overlying yellow sandstones as Jurassic. 
Most of my specimens were obtained from the base of the yellow sandstone series, a few feet 
above a bed of coal containing plants having a general resemblance to those of the Jurassic of 
Europe. The fossils associated with dA. percarinatus are Gryphea Pitcheri, both forms, and 
Inoceramus Crispi (? 
In the same group of rocks which contain these molluscous fossils, both above and below 
them, I found impressions of leaves of several species of dicotyledonous trees, the whole 
affording conclusive evidence of the Cretaceous age of the formation. The lithological char- 
acter of the strata, as well as their superposition and observed continuity, contribute to the 
same conclusion, and assist to establish an identity of geological age between the yellow sand- 
stones and shales of western New Mexico, the reddish yellow sandstones of eastern New Mexico 
and western Kansas, the Lower Cretaceous strata of the Upper Missouri, (Nos. I and II of 
Messrs. Meek and Hayden’s Cretaceous section,) and the red sandstone with impressions of 
leaves of New Jersey. 
NAUTILUS.  Breynius. 
NavTILus, Sp. 
A fragment of a large Nautilus was obtained from the limestone which underlies the red sand- 
stones and variegated marls at Agua Azul, near the base of Mount Taylor. It is too imperfect 
for satisfactory description, exhibiting a portion only of the external whorl. 
It evidently comes near N. planovolvis, Shumard, having similar flattened sides, rounded 
angles, and slightly arched dorsum, but the septa are nearly straight on the dorsum, while in 
the species to which I have compared it they are much curved. 
This fossil is associated with Productus, Allorisma and Bellerophon, but unfortunately all are 
badly preserved, and scarcely susceptible of specific determination. 
The rock containing them is a cherty limestone, much like that wich contains Productus 
semireticulatus, Spirigera subtilita, &c., at the top of the section on Cataract creek, (p. —.) It 
holds the same position in relation to the overlying sandstones and marls as the limestone at 
the crossing of the Littlé Colorado, that at Ojo Vernal, and Pecos, &c. 
It is probably Upper Carboniferous; its surface limiting that series, and perhaps containing a 
mingling of Permian and Carboniferous forms. 
BELLEROPHON. Montfort. 
I obtained a cast of a species of this genus from the limestone at Agua Azul. The specimen 
was too imperfect for specific determination, but it has the aspect of B. Urii, and is, probably, 
a erst nia species. . 
