DESCRIPTION OF THE COLLECTION. 111 
the hardness of feldspar, but without distinct cleavage. They do not exceed one-eighth of an 
inch in length, and are sparsely distributed. 
No. 56. Mojave river.—A compact brownish-red rock, filled with small and thin crystals 
of glassy feldspar, forming a porphyry. This character is not, however, evident, without close 
inspection and the aid of a glass. Small grains of quartz are also distributed, and several minute 
crystals of brown mica were observed. The feldspar crystals appear to be distributed in parallel 
planes throughout the rock. 
No. 57. Mesa, near Gila river. —A. fragment of volcanic scoria or cinder, full of large cavi- 
ties, and very porous. It is black, and one of the surfaces has a green glaze, and is quite 
smooth. The curves and folds which it presents show its former plastic condition. This speci- 
men was probably taken from a transported mass, and was obtained by Lieutenant A. W. 
Whipple when on the boundary survey, and giveu to Mr. Marcou. 
No. 58. Hough and Ready.—This is a compact, hard trap or greenstone, apparently magne- 
sian, and breaking with a brilliant crystalline surface, sbowing cleavages of imperfect feldspar 
crystals. This is from the auriferous region of Grass valley—Rough and Ready being a mining 
locality near that town. 
STRATIFIED ROCKS AND GYPSUM. 
[No. 59 to No. 88.] 
No. 59. Delaware mountain.—This is a light-drab or yellowish limestone, charged with 
small cylindrical stems of encrinites, which are seen most distinctly on the weathered surfaces. 
These fossils are crystalline, while the surrounding rock is amorphous. Mr. Marcou considers 
this rock as belonging to the mountain or lower carboniferous limestone. 
No. 60. From the foot of the Llano Estacado.—This limestone specimen has a curious appear- 
ance, being full of small cavities, and resembling a mass of slag from a furnace. The interior 
surface of the cavities is very irregular, and is as smooth as if glazed by heat. It is, however, 
completely infusible, and its peculiar vesicular condition must be due to aqueous action. Its 
color is a peculiar drab or ash-grey, not easily described. "There are no traces of fossils or of 
stratification. 
No. 61. San Antonio.—This is the largest and heaviest specimen of limestone in the collection. 
It has a dark bluish-grey color; is hard and compact, with a fine, even grain. Itis very tough, 
and if it can be obtained in large blocks, will be valuable for building purposes. "There are no 
traces of fossils in the specimen, which appears to have been part of a stratum an inch and a half 
thick. This rock when heated emits a slight bituminous odor, but it is not perceptible when 
the mass is struck by the hammer. If a solution of this rock be freed from lime, and then 
treated with phosphate of soda, a very abundant precipitate of magnesia is at once obtained. It 
may be regarded as highly magnesian. 
No. 62. Colorado Chiquito.—This specimen greatly resembles that last described, and has a 
similar grain and color. It has apparently been more exposed to the weather, and has a lighter 
color. The mass breaks with curved surfaces. 
No. 63. Shady creek, Camp No, 42.—This specimen is a light-drab colored limestone, saccha- 
roidal, fine-grained, and compact. It is a hard, firm rock, and is suitable for building. One 
of the weathered surfaces shows indications of fossils, but they are not sufficiently distinct to be 
recognised. 
No. 64. Camp No. 30, near the mounds.—This is a red, porous limestone. Its red color is 
distinct, and like that given by per-oxide of iron. The mass is so porous and full of small cavi- 
ties, that it resembles a sponge, and on one of the surfaces, which is weather-worn, the little 
cavities are well exposed, and are so regular and even in their size, and so closely arranged, 
that it gives the specimen an organized appearance, and suggests a coralline origin. 
— No. 65. Camp No. 46, at the foot of the Llano Estacado.— Mr. Marcou has labelled this speci- 
