112 
GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
men “ Sandstone of the upper Trias.” It is a grey, friable, calcareous sandstone, crumbling 
away under the fingers. It effervesces violently with chlorohydric acid, and in addition to the 
siliceous grains, has a considerable amount of white mica disseminated in planes parallel to the 
stratification. It much resembles recent or Tertiary sandstone. The broad and tabular surface 
of the specimen is marked with parts of hieroglyphic characters cut by the Indians. 
No. 66. Shady river, Camp No. 42.—Variegated marl, red and clay colored. It emits a 
strong argillaceous odor when breathed upon, and effervesces with acids. This is from the 
Trias, according to Mr. Marcou. 
No. 61. Between Delaware mountain and Beavertoiun. —This specimen is labelled by Mr. 
Marcou u Red and white clays of the Trias.” The mass was evidently soft and plastic when 
collected, and in its color resembles No. 66, just described. It is very fine, and consists chiefly 
of clay and carbonate of lime. It effervesces freely with acids. 
No. 68. Antelope Hills, Camp No. 36.—This is a white sandstone, with a dark-grey weathered 
surface. The specimen presents a remarkable resemblance to several of the sandstone specimens 
collected by Captain Pope near the 32d parallel. The grains are siliceous, white and yellow, 
and are cemented by a large quantity of amorphous white carbonate of lime ; in fact the grains 
seem rather to be imbedded in a paste of carbonate of lime. It most resembles No. 29 of 
Captain Pope’s collection, found on the surface of the Llano, forty miles east of the Rio Pecos. 
The evidences presented by the fossils collected by Captain Pope led to the conclusion that the 
sandstone of the Llano was Cretaceous, and I am inclined to refer this specimen to that age. 
Mr. Marcou considers it as from the upper Trias. 
No. 69. Betiveen Camps No. 31 and No. 32.—This specimen consists almost wholly of per¬ 
oxide of iron, or Limonite, and is apparently the result of infiltration of a solution of iron 
among the strata of the formation in which it occurs. Its stratified character is evident on 
inspection, and it appears to have resulted from the decomposition of a layer of small bivalve 
shells, casts of which are visible, hut they are so obscure that the species cannot he recognised. 
No. 10. From the foot of the Llano Estacado, probably at Gypsum creek. —This specimen is 
one of a series of beautiful masses of red and white gypsum. This is a dark-red mass, a part 
of it amorphous or granular, and somewhat porous, and the remainder crystalline, cleaving 
with irregular radial surfaces. Its dark-red color—like that of well-burned bricks—appears to 
he due to the presence of a large quantity of per-oxide of iron, which is so abundant and uncom¬ 
bined on one side of the specimen that it rubs off upon the fingers and label, giving the charac¬ 
teristic color of rouge, or red ochre. Mr. Marcou considers this specimen to he from the middle 
division of the Trias. (Trias moyen.) 
No. II. Gypsum creek. —Red crystalline gypsum. A fine large specimen, with the crystal¬ 
line plates arranged in radial or plumose groups slightly curved, and each plate being only 
about one-eighth or three-sixteenths of an inch broad, and from one to three inches long. 
Their brilliant surfaces inclined in different directions, together with the peculiar deep-red 
color, render the specimen very interesting. Small plates of clear crystalline gypsum (selenite) 
are seen in several places imbedded in and among the red plates. The red portions do not 
cleave as readily as clear, colorless selenite, and are more brittle. A thin plate held to the 
light is translucent, and transparent in places, and the coloring matter, which is per-oxide of 
iron, does not appear to be evenly distributed. It is a mechanical mixture, and has probably 
influenced the crystallization. 
No. 12.-?.—A mass of red and white gypsum in small irregular crystal¬ 
line plates, about one-quarter to one-half of an inch broad, confusedly mingled together. The 
predominant color of the mass is red, and it probably came from the same locality as the 
preceding, or near it, but there is no label attached to the specimen. 
No. 13. Canadian river. —A fragment of colorless crystalline gypsum, selenite, perfectly 
transparent and very beautiful. At one end there is a slight depression, partly filled with very 
perfect and clear rhombohedrons of dolomite, (carbonate of lime and magnesia.) These crys- 
