PYRAMID MOUNTAIN—CRETACEOUS FOSSILS. 25 
this resemblance, and we are indebted to him for the first observations upon the extent and ele- 
vation of the hill. Its circumference at the base was found to be nearly six miles, its height about 
700 feet, and the area of the summit about 230 by 370 yards.! I do not find any description of 
` the strata of this mound in the notes of Mr. Marcou, but I do not doubt, from the statements of 
Lieutenant Whipple, that they agree exactly with in ofthe Llano. This is also indicated by 
the fact that the slopes of the mound are covered with cedars, exactly as on the northern slopes 
of the Llano. We have also the section of Pyramid mountain, by Mr. Marcou, which is not 
far distant, and may be regarded as an exhibition of the mineral character of the Tucumcari and 
of the Llano. 
Pyramid Mountain.—The finest and most complete section of the horizontal strata of the 
bluffs along the route was obtained at this mountain by Mr. Marcou. The point was pecu- 
liarly favorable, being one of the isolated mounds, a remnant of the Llano, and exposing the 
strata on all sides. It is only one of the many mounds dotted over the wide space eroded by 
the river from the Llano, and called Plaza Larga by the Mexicans. This mound was ascended 
by Mr. Marcou, and others of the party, and we find the following record of the succession of 
the strata in the notes under date of September 22: 
SECTION AT PYRAMID MOUNTAIN, 
White limestone 
Yellow Missione with bluish- “grey bed at the bottom. 
Bed containing Ostrea 
White sandstone. 
Yellow sandstone. 
White sandstone. 
Grey and green bed in contact with the superior Trias. 
Red and green sandstone. 
White marls with concretions. de e 
Red and green marls. |. umo 
White. 
| Red. 
Mr. Marcou considers that the base of this mound is formed of the beds of the superior Trias, 
the upper portion being Jurassic. It does not appear to me that the evidences are sufficient to 
warrant this decision, but the discussion of this subject will be left for a subsequent portion of 
the report. 
A sketch of this mound was carefully taken in colors by Mr. Mélthausen, the tints agreeing 
as nearly as possible with those presented by the strata. The sketch has been lithographed and 
is appended. It will serve to convey an idea of the relations of the strata, especially the white 
and red series, and may be received as an exhibit of the general aspect of the bluffs of the Llano, 
where the beds are exposed. The section and locality derives great interest from the occurrence 
of fossils. The bed containing the Ostrea is said to be of greyish-blue clay and sub-schistose, 
and two inches thick. The Ostrea is subsequently called Ostrea dilatata, and is again mentioned 
in the Resumé, This i is the fossil called Gryphea Tucumcari in the collection (No. 133) from 
Pyramid mountain, and referred to in the Resumé under the same name, it being said to have 
the greatest analogy with the Gryphea dilatata of the Oxford clay.* It probably is a new species 
or a variety of | ryphea Pitcheri, and a description of it will be found in Chapter IX, under the 
name G, Tucumearii, originally proposed by Mr. Marcou. See also Plate I. 
From these various observations we may conclude that the great plateau, the Llano Estacado, 
consists of horizontal strata of light-colored white, or greyish-white, and yellowish sandstones, 
and bluish clays and marls, resting conformably upon beds of red clay, red sandstone, and 
gypsum, and these, accor ing to Mr. Marcou, are intercalated with greyish or light-colored 
« Report ofthe ronte from Fort Smith to Santa Fé 1849, p. 14. 
c na i: | in the original. Tt Tacks ho OMM: w. P. B 
t: Jurassic. 
500 feet 4 
5 
