OF NORTH AMERICA. 
17 
I have mentioned two points between Topofki creek and Anton Ghico where the Triassie Hocks 
are covered by more modern formations. The first of these points is upon one of the tributaries 
of the False Washita river — Comet creek (latitude 85°, 32', 21"; longitude 99°, 14', 40".) — near 
our camp N°31, where upon the heights, are found the remains of beds of a limestone filled with 
shells , which 1 connect with the Neocomian of Europe ; or , in other words , with the Lower Divi- 
sion of the Cretaceous Hocks. This limestone is only five feet thick; it is of a whitish-gray color, 
containing an immense quantity of Ostracea, which 1 consider as identical with the Exogyra (Gry- 
ph®a) Pitcheri Mori. (PI. IV., fig- 5., 5 a, 5 b, and 6.); having the closest analogy with the Exogyra 
Couloni of the Neocomian of the environs of Neuchatel (Switzerland). As it is the first time the 
Neocomian has been recognized in North America, where, until now, only the Grcen-Sanct and Chalk- 
Marl or Lcmer Chalk, have been found, 1 will add that these strata are much more developed at 
Fort Washita, where Dr. G. G. Shumard has made a large collection of fossils, such as; Pecten 
guadricostatus , Gryphaia Pilcheri , Cardium multislriatum , Ammonites acuto-carinatus , Holaster simplex ; all 
fossils or genera characteristic of the Neocomian of Europe. Further, at Fort Washita, the Neoco- 
mian is covered by the Green-Sand, containing very fine Hemiaster , large Ammonites flaccidicosta , Gry- 
phcea sinuata var. Americana, Exogyra TexanaC^, etc. 
This Neocomian has been almost wholly destroyed and carried away by denudations ; for it is 
only found on the summits of the hills, where it appears like ruins of ancient buildings; it occupies 
actually only a width of three or four miles. Probably at the time of the deposit it covered more 
space; but, as at Fort Washita, where it has been very little denuded, it is only twenty-five or 
thirty miles wide. This shows it to have been but a narrow band in the immense basin of the 
Prairies. 
The second point where the expedition has quitted the strata of the Trias for a more recent 
formation , is at the place where we crossed the Llano Estacado (latitude 35°, 17', 18"; longitude 
102°, 53', 24".). The base of the Llano is formed wholly of the upper strata of the Keuper, which 
reaches half way up the height of the plateau. These strata, which are of a red color, are sud- 
denly replaced by white sandstone, containing numerous calcareous concretions, then by a com- 
pact white limestone, sometimes oolitic, that forms the summit of the Llano. These beds are su- 
perposed in concordant stratification upon those of the Keuper. 
The Llano Estacado consists of two table-lands of different elevations. We crossed the lower 
one; but forty miles further west, near Fossil Creek and Tucumcari Mount (latitude 35% 01', Ifi"; 
longitude 103°, 52', 29".), there is a secojid steppe, one hundred and fifty feet higher than the 
first, also forming a vaste mesa, which extends to the Pecos. This second mesa^) is entirely formed 
1) See: Fossils of the Cretaceous period, jiages 204 and following, by Dr. B. F. Shumard; in the 
Exploration of the Hed river of Louisiana in the year 1852, by Capt. R. B. Marcy. AVashington , 1853. 
2) Our camp N° 49 on the Tucumcari creek, in a beautiful valley called by the Mexicans Plaza 
Larga, w'as environed by high hills called Big Tucumcari, Little Tucumcari, Monte Revuelto and the cliffs of the 
northern side of the Llano Estacado. A bettor locality for geological explorations is seldom met with; but un- 
happily the situation is very inaccessible, in the middle of the country over which the Comanche In- 
dians range; exploration without a strong escort is very dangerous; and at that time the expedition was 
progressing rapidly towards the AA'est. Hurried by the fatigue of men and animals, we were looking 
