Page 28 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

GENERAL FEATURES 27
with thin layers of bluish limestone, and at the top a light-colored highly fossiliferous subcrystalline limestone 60 feet thick. In the Sierra Caballos the formation consists of light-colored mas- sive to slabby, mostly coarse-grained limestone from 100 to 200 feet thick. In the canyon north of Kingston and near Her- mosa are many exposures of the Lake Valley limestone. The crinoids and other fossils yielded by the Lake Valley limestone indicate that it is of early Mississippian age. The formation rests on the Percha shale without discordant attitude, and is overlain by limestone of Pennsylvanian age without difference in attitude but separated by a break representing a long interval of late Mississippian time.
PENNSYLVANIAN SYSTEM
Magdalena Limestone.—The thick limestone succession of the Magdalena limestone is a prominent feature of the Fra Cris- tobal, Cuchillo and Black ranges, and in the Sierra Caballos this limestone is the predominant rock, but interbedded sandstone and shale occur in all sections. In Sierra County the Magdalena limestone consists for the most part of massively bedded blue and gray limestone, interstratified with which are thin-bedded limestones and dark blue shales. Here and there a thin bed of sandstone occurs. At Kingston the basal strata consist of about 300 feet of dark blue and gray limestone in thick beds with thin shale partings. The upper portion is also about 300 feet thick and consists chiefly of blue and drab shales interstratified with several limestone strata 15 to 20 feet thick. Two miles east of Hermosa, Palomas Creek has cut a gorge 1,000 feet deep, the walls of which are nearly vertical and consist almost wholly of blue and gray limestone of the Magdalena formation. The lOwer half of the escarpment consists of limestone and shale in about equal amounts ; the upper portion is made up of hard, massively bedded gray limestone. About half way up the cliff a few thin beds of quartzite are interbedded with the limestone. In the Sierra Caballos the formation is represented chiefly by limestone, with some shale beds in the basal part, as at Hermosa. In other parts of the State the Magdalena limestone has been divided into a lower and an upper formation known respectively as the San- dia formation and the Madera limestone, but at no place in Sierra County was it possible to make this division with certainty.
PERMIAN SYSTEM
Abo Sandstone.—The red strata of the Abo sandstone, the basal formation of the Permian, outcrop at several places in Sierra County, the most extensive areas being on the east slopes of the Fra Cristobal, Caballos, and Cuchillo ranges, and in the Black Range from just west of ChlOride to as far south as Kingston. The Abo sandstone lies unconformably upon the Magdalena lime- stone and consists in the main of slabby sandstone of deep red- dish-brown color intercalated with arkosic beds and red sandy