Page 202 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

198 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
Farther north in Palomas Gap and vicinity, faulting has con- cealed the Fusselman and all other formations below the Magda- lena limestone.
Percha Shale.—Above the Silurian beds in the central and southern parts of the range is the Percha shale of Upper Devon- ian age. This formation outcrops in a slope of moderate inclina- tion, in marked contrast to the cliffs below and above it, and consists of black to gray and greenish-buff shale and thin-bedded sandstone and limestone measuring 200 feet and upward in total thickness. The lower portion of this shale is generally darker in color than the upper portion, which is usually gray to buff. The upper part contains many thin layers of gray limestone.
Lake Valley Limestone.—Above the Percha shale and below the Pennsylvanian rocks is limestone 105 feet thick that corre- sponds stratigraphically and in general appearance with the Lake Valley limestone of other nearby sections.
Magdalena Limestone—This formation, which is approxi- mately 600 feet in thickness, forms the top of the Sierra Caballos for the entire length of the range. It consists largely of light- colored limestone and a few interbedded shale members. Near the top is a bed of black shale, similar to the shale found in nearly every other exposure of the Magdalena in Sierra County. This shale varies in position from the middle of the section to, near its present top, depending on the amount of erosion that the forma- tion has undergone. It is quite probable that the top of this shale marks the division between what is called the Sandia or lower formation of the Magdalena limestone and the Madera on upper formation in other districts.
Abo Sandstone.—The Magdalena beds are unconformably overlain by the Abo sandstone wherever the contact is visible. The Abo formation is about 800 feet thick, and is composed essentially of red sandstone and red sandy shale, with a few hard layers of pink to buff sandstone. Near the middle of the section is a thin bed of gray sandy to shaly limestone. The Abo beds outcrop for almost the entire length of the range.
Chupadera Formation.—The Abo beds give place abruptly to the overlying gypsum and limestone strata of the Chupadera formation. The basal part of the Chupadera, consisting of the red sandy shales and gypsum beds of -the Yeso formation, is of unknown thickness, as these strata form the floor of a flat valley between the Abo and San Andres rocks in this area. The lower part of the San Andres formation, which is the upper member of the Chupadera, consists of alternating beds of limestone and gypsum having a thickness of 250 to 400 feet. Next is 50 to 200 feet of limestone with subordinate beds of gypsum, then 50 feet of sandy shale, and at the top, 25 feet of blue limestone.
Mancos Shale.—The San Andres limestone is cut off by a fault to the east, along which sandstone and shale of upper Cre-