GENERAL OUTCROP SECTION OF THE BLACK HILLS AREA FORMATION SECTION THICKNESS IN FEET DESCRIPTION QUATERNARY SANDS AND GRAVELS [illegible] 0 - 5ft Sand, gravel and boulders TERTIARY PIOCENE OGALLALA GROUP [illegible] 0 - 500 Light colored sands and silts. MIOCENE ARIKAREE GROUP [illegible] 0 - 300 Light brown clays and silts White clay bed at base OLIGOCENE WHITE RIVER GROUP Brule Formation 0 - 600 Light colored clays with sandstone channel Chadron Formation fillings and local limestone lenses [illegible] 0 - 485 Light colored clays and sands, with coal near [illegible] farther north. PALEOCENE TONGUE RIVER MEMBER [illegible] 0 - 225 Green marl shales and yellow sandstone, FORT UNION FORMATION "" latter often as concretions CANNONBALL MEMBER So- gray clays and sandstones with LUDLOW MEMBER thin beds of lignite. CRETACEOUS HELL CREEK FORMATION [illegible] 425 Sando, colored soft brown shale and gray (Lance Formation) (Lance Formation) sandstone, with thin lignite lenses in the upper part. Lower half more sandy. Hay lignite concretions and thin lenses of iron carbonate. FOX HILLS SANDSTONE [illegible] 25 - 200 Greyish-white to yellow sandstone Calc. UPPER PIERRE SHALE [illegible] 1200-2000 Principal horizon of limestone lenses giving tepee buttes Dark gray shale containing scattered concretions. Widely scattered limestone masses, giving small tepee buttes. Black fissile shale with concretions. Sharan Springs Nem NIOBRARA FORMATION [illegible] 100 - 225 Impure chole and calcareous shale. Turner Sand Zone CARLILE FORMATION [illegible] 400-750 Light-gray shale with numerous large Wall Creek Sands concretions and sandy layers. Dark gray shale GREENHORN FORMATION [illegible] (25 - 30) Impure tabby limestone. Weathers buff GRANEROS SHALE (200-350) Dark gray calcareous shale, with thin [illegible] Ormen Lake limestone at base. Belle Fourche Shale [illegible] 300 - 190 Very shale with scattered limestone MOWRY SHALE Clay-sour bentonite at base. NEWCASTLE SANDSTONE Light-gray siliceous shale, fish scales SKULL CREEK SHALE and thin layers of bentonite. Brown to light yellow and white sandstone Dark gray to black shale. LOWER FALL RIVER [DAKOTA (?)] S.S. [illegible] 10 - 200 Massive to sloppy sandstone. FUSON SHALE [illegible] 10 - 188 Gray to purple shale. Thin sandstones. MINNEWASTE LIMESTONE [illegible] 0 - 25 Massive gray limestone Lakota Sandstone Loose, hard, crossbedded sandstone mostly MORRISON FORMATION buff to gray. Conglomerate locally and UNKPAPA SANDSTONE clay at base. SUNDANCE FORMATION Greenish-gray shale, thin limestone lenses GYPSUM SPRING FORMATION Glaucophitic sandstone, red at near middle. NUGGET (?) FORMATION Red siltstone, gypsum, and limestone. JURASSIC SPEARFISH FORMATION [illegible] 0 - 220 Massive fine-grained sandstone. UNKPAPA SANDSTONE 250-450 Greenish-gray shale, thin limestone lenses SUNDANCE FORMATION Glaucophitic sandstone, red at near middle. GYPSUM SPRING FORMATION Red siltstone, gypsum, and limestone. NUGGET (?) FORMATION Massive crossbedded siliman sandstone. TRIASSIC SPEARFISH FORMATION [illegible] 300 - 700 Red sandy shale, soft red sandstone and [illegible] siltstone with gypsum and thin limestone Gypsum locally near the base. Massive gray, laminated limestone. PERMIAN MINNEKAHTA LIMESTONE [illegible] 30 - 50 Red shale and sandstone PENNSYLVANIAN OPECHE FORMATION [illegible] 50 - 135 Yellow to red cross-bedded sandstone, MINNELUSA SANDSTONE limestone, and anhydrite locally of "top [illegible] interbedded sandstone, limestone, dolomite, Red shale with interbedded limestone and siltstone at base. [illegible] MISSISSIPPIAN PAHASAPA (MADISON) LIMESTONE [illegible] 300-630 Massive light-colored limestone ENGLEWOOD LIMESTONE Dolomitic in part. [illegible] Pink to buff limestone. Shale locally at base. [illegible] Shell dolomite and limestone. ORDOVICIAN WHITEWOOD (RED RIVER) FORMATION [illegible] 0 - 60 Green shale with siltstone of top and WINNIPEG FORMATION white sandstone at base. [illegible] Massive to buff sandstone. Greenish DEADWOOD FORMATION glauconitic shale, flaggy dolomite and flat- PRE-CAMBRIAN pebble limestone conglomerate. Sandstone, METAMORPHIC and with conglomerate locally of the base. IGNEOUS ROCKS Schist, slate, quartzite, and arkasic grit intruded by diorite, metamorphosed to amphibolite, and by granite and pegmatite.