Gray Sandstone Research Articles

New Stratigraphic Nomenclature for Upper Devonian of South-Central New York: GEOLOGICAL NOTES

Correlation of post-Tully, Upper Devonian strata is based on the combination of lithology, faunal assemblages, and thicknesses. Black shales are laterally persistent key beds amid interfingering gray shales, siltstones, mudstones, and sandstones. The rate of maximum thickening was found to increase exponentially S. 60 degrees E., using the top of the Tully Limestone as a key horizon. Five formations are recognized in the W.-central area (Watkins Glen-Elmira) and were traced into the eastern part (Ithaca-Owego). At the base is the Geneseo Formation, chiefly black shale, overlain by the Ithaca Formation. The Ithaca is divided into, in ascending order, the Penn Yan, Genundewa, and West River members in the W., and the Sherburne, Renwick, and Treman members in the E. The overlying Middlesex Formation, composed essentially of black shale, consists of the basal Montour Member, the Johns Creek Member, and the upper Sawmill Creek Member. Next above is the Sonyea Formation, represented by the redefined Cashaqua Member in western New York, by the Pulteney, Rock Stream, and Rye Point members (in ascending order) in W.-central New York, and the West Danby Member near Ithaca. The upper formation, the Rhinestreet, consists of, in ascending order, the Moreland, Millport, Dunn Hill, Beers Hill, and Roricks Glen members in the W. To the E., only the Moreland Member is distinguishable, and the upper members are considered part of the Chemung Formation.

Sandsten och kvartsit med flusspatcementerade kvartssfäroider

Summary Sandstone and quartzite with fluorspar cement A gray sandstone and a dark blue quartzite of Lower Cambrian age from around Kyrkberget in southern Swedish Lapland contain large quantities of small white spheroids. This is specially apparent in the dark quartzite (Fig. 1). The spheroids consist of quartz, cemented with fluorspar. The quartz occurs partly in larger, rounded grains, partly in smaller, edged grains. The fluorspar is seen to fill all open spaces between the quartz grains (Figs. 2 and 3). In some cases a reiterated cementation of fluorspar occurs in an outer ring of the spheroids outside a zone of unaltered quartzite (Fig. 4). An analysis of fluorine in the rock, as seen in Fig. 1, gave 5,98% F corresponding to 12.21% fluorspar. The spheroids are assumed to represent parts of the rocks, which originally have had an aggregation of less compact portions which have been more receptive to mineralization. The angular grains of quartz in the spheroids may be ascribed to corrosion by fluorine.

Mesaverde Group in Adjoining Areas of Utah, Colorado, and Wyoming: ABSTRACT

The mixed marine and nonmarine Mesaverde group (Late Cretaceous) overlies and intertongues with the marine Mancos shale or its equivalents and underlies and intertongues with the marine Lewis shale or underlies continental rocks of latest Cretaceous or Paleocene age. The area studied is approximately 200 miles square on both sides of the Wyoming and Utah-Colorado state Formations and members in 7 smaller geographic subdivisions are described and related in terms of Lee's (1915) genetic units to a standard four-fold section in the Rock Springs uplift consisting from oldest to youngest of the Blair, Rock Springs, Ericson, and Almond formations. Data from 14 measured surface sections and more than 120 wells were used to make isopach maps of individual formations, members and tongues. These maps show that basins and relative arches of Late Cretaceous time correspond fairly well with those of Tertiary time and that the maximum thickness of a genetic unit is at the zone of transition from continental to marine sedimentation. Numerous minor transgressions and regressions of the sea are imposed on a general eastward regression during Mesaverde time followed by a major transgression during Lewis time and a complete withdrawal of the sea after Lewis time. There are numerous cyclothems consisting of gray marine shale, tan marine siltstone and sandstone, gray and white beach sandstone, coal, brown carbonaceous shale, and gray to brown carbonaceous siltstone. Both transgressive and regressive deposits are present. Two probable controls of intertonguing are recognized: (1) intermittent delivery of sand and mud by streams along a subsiding delta front and reworking by marine currents; (2) several rather rapid changes of sealevel or landlevel, either tectonic or eustatic. Most of the sediments were derived from areas west of the Wasatch line. Toward the close of Mesaverde deposition, local uplifts in the site of the present Uinta Mountains and possibly the Wind River Mountain provided a source for sediments. Short-ranging fossils are scarce in the Mesaverde group in this area. The marine shale tongues generally contain long-ranging arenaceous foraminifera and the marine sandstones contain Ostrea sp., Inoceramus sp., Halymenites major and worm tubes; the faunas are useful as indicators of paleoenvironments, but are not useful for stratigraphic correlations. No new formation names are proposed. Several unnamed sequences should be mapped and traced laterally before they are named. The Lazeart sandstone is raised from member to formational rank. The Rimrock sandstone and the Asphalt Ridge sandstone of Walton (1944) are considered members of the Iles formation. End_of_Article - Last_Page 954------------

Probable Triassic Rocks Along Eastern Front of Sangre de Cristo Mountains, South-Central Colorado

Sedimentary rocks of Triassic age generally have been thought to be missing from outcrops in the Sangre de Cristo Mountains of Colorado where at most places the Entrada sandstone of Jurassic age rests unconformably on rocks that have been assigned to the Sangre de Cristo formation of Pennsylvanian and Permian age. Two units of probable Triassic age have been separated from the top of the Sangre de Cristo formation; one is here described and named the Johnson Gap formation. The other is correlated with the Lykins formation of central Colorado and in this report is referred to as the Lykins(?) formation. The Johnson Gap formation crops out for 8 mi. or more N. of the Colorado-New Mexico boundary, and is correlated with a part of the Dockum group of Triassic age of northern New Mexico. The Lykins(?) formation crops out in the area of Huerfano Park and locally along the eastern front of the Sangre de Cristo Mountains as far S. as the North Fork of the Purgatoire River. Fossil wood found near the top of the unit has been determined as Triassic(?) in age. The Johnson Gap formation and the Lykins(?) formation differ lithologically and probably are not correlative. The Johnson Gap consists mainly of gray silty conglomeratic limestone interbedded with gray and light red silty and siliceous limestone, red siliceous siltstone, greenish gray and brown plastic shale, and gray fine-grained quartzose sandstone. The Lykins(?) is made up of brownish red, purplish red, and buff sandstone, siltstone, and shale, and a few thin light gray limestone beds. It is probably older than the Johnson Gap formation in that the Lykins(?) formation seems to grade into the underlying Sangre de Cristo formation, whereas the Johnson Gap formation overlies the Sangre de Cristo unconformably. The striking lithologic similarity of the rocks of the Lykins(?) formation along the eastern front of the Sangre de Cristo Mountains to those of the most southerly exposures of the Lykins formation 20 mi. ENE. of Canon City, Colorado, suggests that the rocks once were probably continuous throughout S.-central Colorado, but were locally removed by erosion following a post-Triassic uplift in the general area of the Wet Mountains.

Revision of Colorado Group on Sweetgrass Arch, Montana

The writers propose that the rocks formerly assigned to the Colorado shale on the Sweetgrass arch of northwestern Montana be divided into a lower unit, the Blackleaf formation with four named members, and an upper unit, the Marias River shale with four named members. The Blackleaf formation, of Early Cretaceous age, consists of marine and non-marine rocks that include much sandstone and sandy shale. It is divided into the Flood, Taft Hill, Vaughn, and Floweree members. The oldest member, the Flood, consists of brown-weathering ledge-forming sandstone beds and dark gray fissile shale probably marine in origin. It is 138 feet thick at its type section. The Taft Hill member, a marine sequence that is 240 feet thick as its type locality, consists of greenish gray glauconitic sandstone and gray soft bentonitic siltstone and shale. The Vaughn bentonitic member is characterized by light-colored bentonitic and tuffaceous siltstone that contains small crystals of orange-red heulandite. This non-marine unit is 97 feet thick at its type locality. The Bootleg er member, 330 feet thick at its type locality, is a marine sequence of interbedded sandstone, siltstone, and shale, but includes some layers of bentonite and chert-pebble conglomerate. The Marias River shale, of Late Cretaceous age, consists of 900-1,200 feet of dark gray marine shale. It is divided into the Floweree, Cone, Ferdig, and Kevin members. The Floweree (basal member) is mostly non-calcareous shale and siltstone; it is 63 feet thick at its type locality. The Cone calcareous member, 54 feet thick, consists of calcareous shale, thin beds and concretions of limestone, and some layers of bentonite. Sandy non-calcareous shale characterizes the Ferdig shale member which is 225 feet thick at its type locality. The Kevin shale member, 620 feet thick, contains numerous gray, yellow, and brown limestone concretions and dusky red dolostone concretions as well as many thin layers of bentonite. The middle of the member is marked by the MacGowan concretionary bed, a thi unit of dolostone and limestone that contains pebbles of chert and phosphatic siltstone.

Relations of Certain Upper Jurassic and Lower Cretaceous Formations in Southwestern Oregon

The Myrtle formation in southwestern Oregon is herein considered to be a group, as originally proposed by Louderback, and is subdivided into the Riddle and Days Creek formations. Some of the Myrtle formation as mapped by Diller is excluded from the Myrtle group and is reassigned to the Dothan formation. The Riddle formation consists dominantly of gray siltstone, is about 1,000 feet thick, and contains fossils of latest Jurassic (Portlandian--middle to late Tithonian) age. The Days Creek formation consists mostly of alternating units of greenish gray massive sandstone and siltstone, is at least 2,000 feet thick, and contains fossils of Early Cretaceous (Valanginian to Barremian) age. The Riddle formation rests with angular unconformity on the older Jurassic Galice, Rogue, nd Dothan formations. The Days Creek formation rests concordantly on the Riddle formation, and locally overlaps onto older Jurassic rocks. The contact between the Riddle and Days Creek formations is considered to be a disconformity involving the Berriasian and part of the Valanginian stages.

Stratigraphy of Pennsylvanian, Permian, and Lower Triassic Rocks of Confusion Range, West-Central Utah

Work by the United States Geological Survey in the Confusion Range of west-central Utah during the past few years has resulted in the accumulation of considerable data regarding the stratigraphy of rocks ranging in age from Late Mississippian through Early Triassic. These rocks are here discussed as six formations, whose physical limits more or less coincide with the boundaries selected by earlier workers in the area, although considerable changes in stratigraphic nomenclature have been made. The Ely limestone of Late Mississippian, Early and Middle Pennsylvanian, and Permian age consists of 1,850-2,000 feet of alternating resistant thick-bedded limestone and slabby slope-forming limestone. The upper 100-350 feet of the formation contains an early Permian fauna and is generally more massive and less cherty than the remainder of the formation, which contains a fauna characteristic of the lower half of the Pennsylvanian and locally Late Mississippian. A hiatus representing Late Pennsylvanian time separates Middle Pennsylvanian and Permian faunas. The Arcturus formation, which conformably overlies the Ely limestone, consists of poorly indurated yellowish gray calcareous sandstone with thin, ledge-forming interbeds of dark gray to tan limestone and dolomite. The few fossils found in the Arcturus formation, and its stratigraphic position, suggest that the formation is early to middle Permian in age. The total thickness of the formation is uncertain, but a minimum thickness of 2,700 feet has been measured. The succeeding three formational units, the Kaibab limestone, the Plympton formation (new name), and the Gerster limestone, all of Permian age, have been included in the Park City group. The Kaibab limestone overlies the Arcturus formation and consists of 480 feet of somewhat cherty bioclastic limestone. The lithologic character of the Kaibab is in sharp contrast to the succeeding unit which is here named the Plympton formation and is predominantly dolomite and chert. The Plympton formation is 690 feet thick and contains phosphatic beds believed to be lithologic correlatives with parts of the Park City formation of northwestern Utah. The overlying Gerster limestone consists of 1,100 feet of very fossiliferous cherty bioclastic limestone and argillaceous limestone. The Gerster limestone is the youngest Permian unit in the Confusion Range. Like the Kaibab, it is differentiated from the Plympton formation by its high limestone content and lack of dolomite. The contact be ween the Plympton and the Gerster limestone is conformable throughout the area. The Kaibab limestone, the Plympton formation, and the Gerster limestone are believed to be correlative with units within the Park City and related formations of nearby areas in northern and northwestern Utah and northeastern Nevada. In areas south of the Confusion Range, the younger Permian units, the Plympton formation, and the Gerster limestone, are absent and only the Kaibab limestone is present in the Grand Canyon area. The Thaynes formation of late Early Triassic age consists of thick beds of predominantly greenish gray calcareous clay shale interbedded with thin beds of gray to chocolate brown limestone, and is more than 1,900 feet thick in the Confusion Range. It is unconformably overlain by Tertiary and Quaternary strata, and no younger Mesozoic rocks crop out in the area. The contact of the Thaynes formation with the underlying Gerster limestone appears conformable; however, faunal evidence indicates a considerable hiatus between the two formations.

Pigeon Point Formation of Late Cretaceous Age, San Mateo County, California: GEOLOGICAL NOTES

Upper Cretaceous beds near the town of Pescadero in San Mateo County are named the Pigeon Point formation. The Pigeon Point crops out in a belt less than 2 mi. wide which extends from Pescadero Point S. to midway between Franklin Point and Ano Nuevo Point, a distance of approximately 10 mi. The rocks exposed in the coastal cliffs in the above area constitute the type section. The thickness of the formation probably exceeds 8,500 ft. The beds consist mainly of brown and greenish gray sandstone with some siltstone, mudstone, and conglomerate. On the basis of mollusks, including ammonites, and Foraminifera, the Pigeon Point formation is in part Campanian in age and probably younger. In no way - fauna, lithology, thickness or age - does the Pigeon Point resemble the type Chico formation.

Petalodus (Bradyodont) from the Permian of Kansas and Oklahoma

Artinskian of Russia. This specimen was first reported by Karpinsky (1899; 387), the area of Dewitshja-Berges, westward there from, two versts from Krasnoufimsk, there is exposed in a quarry, a bright grey and yellowish-grey sandstone. Its present thickness is five meters, and it is platy. In the beautiful paleontological collection that A. Bessonoff collected in that quarry and presented to the Natural Science Society of the Urals, Th. Tschernyschev, A. Gregoryeff and I have determined the following forms-Petalodus-. (senior author's translation).

New Geologic Formation Names in Jackson Hole, Teton County, Northwestern Wyoming

Four new formation names are used herein for hitherto undescribed or inadequately described rocks in the Jackson Hole region, Teton County, Wyoming: The name Harebell formation is used for a 5,000-foot succession of quartzite pebble conglomerate, olive-drab to gray sandstone, drab-colored siltstone, claystone, and shale of Late Cretaceous age unconformably overlying older Cretaceous rocks and unconformably overlain by Paleocene and younger Tertiary rocks. The name Colter formation is used for a 7,000-foot sequence of white, gray, green, and brown, water-laid basic pyroclastic conglomerate, tuff, sandstone, and claystone of middle Miocene age, unconformably overlying all older rocks and unconformably overlain by rocks of middle Pliocene age. The name Teewinot formation is used for 5,000 feet or more of white limestone, pumicite, tuff, claystone, diatomite, and conglomerate of middle Pliocene age, unconformably overlying all older rocks and unconformably overlain by strata of late Pliocene or Pleistocene age. The name Bivouac formation is used for 1,000 feet of poorly lithified conglomerate interbedded with less amounts of sandstone, siltstone, claystone, pumicite, and welded rhyolite tuff of late Pliocene or Pleistocene age, unconformably overlying rocks of middle Pliocene age, and unconformably overlain by glacial and integlacial deposits of Pleistocene age.

Clay Minerals in Three Podzol Profiles

AbstractClays from well‐developed podzols from gray acid sandstone glacial tills of Kansan, Illinoian, and Wisconsin ages were identified. After removal of the free oxides, the predominant minerals in the clay were interstratified 2:1 layer silicates, quartz, illite, and small quantities of kaolinite. Vermiculite or chlorite was present in the lower horizons of the older tills. The A2 horizons tended to be higher in quartz than the B and C horizons. Wisconsin clays were slightly higher in quartz than Illinoian or Kansan. The clays, while showing slight shifts with age and depth, were basically similar.

The Sespe Formation of the Santa Barbara Embayment.: ABSTRACT

The Sespe formation, composed of red, buff, and gray sandstone and conglomerate, and red and green siltstone, has a landward extent of about 1,250 square miles, and a volume of about 950 cubic miles. Its seaward extent may be greater or much less than that on land, since its presence in the Channel Islands chain is confined to Santa Rosa Island. Its maximum thickness of about 7,000 feet is found in the Simi Valley, near the formation's present east margin. In general the formation thins westward, due in part to gradation into beds of definite marine character. The Sespe has an age range possibly as great as from upper middle Eocene to middle Miocene. The formation's vivid colors and scarcity of organic matter, especially in its eastern portion, combined with its lateral gradation into beds of undisputed marine character, are suggestive of a non-marine origin for the bulk of the formation. The Sespe does not appear to be a unique unit from the standpoint of time-lithology association. Many other sedimentary basins in Southern California possess similarly appearing rocks occupying about the same place in the geologic column. It would seem that widespread climatic and orogenic factors contrived to produce these formational cousins at about the same time. Sespe oil production has been established over an east-west belt 90 miles long. Current production from the Sespe is about 17,000 barrels daily, 95% of which comes from fields on the 17-mile-long Oak Ridge uplift. Different zones in the Sespe formation produce from field to field, even along Oak Ridge, in a manner suggestive of varying or multiple sources for the Sespe's oil. End_of_Article - Last_Page 2776------------

Permo-Triassic geology of south Cumberland and Furness

The Permo-Triassic rocks flanking the Duddon Estuary dip south-westward in three fault blocks defined by major N.N.W. faults downthrowing west. The Zechstein deposits include Brockrams (breccias) accumulated near the old Lake District landmass, passing south-westward into St. Bees Shale and Magnesian Limestone. Still farther from the old shore-line, the limestone gives place to massive anhydrite. Among the Zechstein sediments are grey, plantbearing dolomitic siltstones, possible equivalent to the Hilton Plant Beds and Marl Slate farther east. The Bunter is represented by sandstone (St. Bees) 2,500 feet thick. Evidence is presented to show that in Furness the Bunter overstepped the Zechstein to rest directly on the Carboniferous limestones, and it is suggested that the haematite “sops” of that region originated in swallow holes formed beneath the sandstone. After mineralisation by solutions whose origin is still in doubt, further solution without mineralisation caused collapse and brecciation of the ore-bodies. The Keuper includes grey (Kirklinton) sandstone, overlain by marl with halite deposits. The simplest interpretation of the subsurface geology beneath Walney Island suggests that the halite deposits are lenticular in form, and at different stratigraphical levels. Petrographical descriptions of the sediments and evaporites are included.

Oldman and Foremost Formations of Southern Alberta

The Oldman and Foremost formations comprise an easily recognizable stratigraphic unit in Southern Alberta because of their lithologic character and position between marine strata. The Oldman is a continental type of deposit consisting essentially of light gray sandstones and gray shales. The Foremost formation underlies the Oldman conformably, and is brackish-water in origin. It is composed of sandstones, silts, shales of darker hues than those of the Oldman, and coal seams. These formations were laid down at or near the margins of the Bearpaw and Pakowki seas; hence, marine phases occur in the Foremost, and brackish-water phases in the Oldman. Thickness of the combined formations varies from 1,600 feet near the southwestern foothills to 600 feet in the eastern part of Al erta.

Fossil Polypores from Idaho

In June, 1946, we spent a day searching for fossil plant remains in the late Tertiary deposits in southwestern Idaho. Our primary quest in this region was for petrified evergreen cones that have occasionally turned up, although only in such quantity as to whet the appetite of collectors. The focal point of that day's collecting was approximately 10.5 miles south of Bruneau and .5 mile east of state highway No. 51 which runs-south Mountain Home, Idaho, through Owyhee County into Nevada. In the course of the day one member of our party, Mr. J. M. Dodds, a County Commissioner, of Boise, discovered a fine specimen of a petrified polypore. More recently, Mr. S. H. Osgood, of Rupert, Idaho, has sent us a fragment of another specimen. Although both of our specimens seem to be clearly referable to -the fossil Fomes idahoensis Brown (Brown, '40), in view of the great rarity of fossil polypores a brief record of the specimens seems worth while. This part of Idaho is well known to local mineral collectors for its abundance of fossil wood, as well as the occasional cones. Most of these fossils are weathering out of a loosely consolidated, fine white sandstone which is overlain by a brownishbuff sandstone of a harder texture likewise yielding petrified plan't remains. Overlying the productive plant beds is a horizon which yields an abundance of wellpreserved, fish jaws (Mylocybrinus robustus Leidy). The only stratigraphical study of the beds in this region is that of Piper's ('24), and the horizon which our fossils were obtained was apparently in his group No. 8 which is described as Lake sediments, semi-consolidated, white, gray, and buff sandstones and sandy shales, volcanic ash; .... These beds have been considered to be of Pliocene age although it is possible that they may be of later origin. In a recent letter (February 20, 1947) Dr. Bobb Schaeffer has informed us of a collection of Mylocyprinus robustus fossil fish pharyngeals in the American Museum that were collected from an area in southwest Idaho between 'Catherine and Sinker Creeks.' This particular locality is considered to be Pleistocene and as this genus has not previously been reported older formations I am wondering if your horizon might not also be referable to that period.

A Deep Boring at North Creake, Norfolk

Summary1. The North Creake boring shows the Chalk up to the Coranguinum zone to be appreciably thicker than at the nearest outcrops. The Chalk rests upon fine-grained Upper Greensand (possibly Albian) which is developed in addition to the normal Red Chalk.2. The “Lower Greensand” is developed much as at outcrop, but the Sandringham Sands are thickened by one-third. There is a strong indication of a stratigraphical break in the middle of the Carstone, which may mark the boundary between the Aptian and Albian stages.3. The Kimeridge, Corallian (Ampthill), and Oxford Clays are developed as in the King's Lynn district, and (in contrast to Southerey) normal Kellaways Beds rest on Cornbrash.4. The upper part of the Great Oolite Series is in Blisworth Clay facies. The “Limestone” is raggy and non-oolitic.5. The Great Oolite rests directly on bituminous shales which are believed to be of early Upper Lias date. The Middle and Lower Lias are well developed, but the latter is attenuated as a whole. There is a possible representative of the Lower Rhaetic.6. The Trias is represented by varicoloured marls (Keuper) upon pale grey sandstone (probably Bunter). The latter rests directly on pre-Cambrian rocks comparable with tuffs and agglomerates of Chamwood.

CONTINENTAL-MARINE MISSISSIPPIAN RELATIONS IN NORTHERN PENNSYLVANIA

The marine Mississippian of northwestern Pennsylvania meets and merges in north-central Pennsylvania with the continental Mississippian spread from the northeast. At their junction, the two facies are confined between the overlying Olean or Pottsville spheroidal-pebble conglomerates of the basal Pennsylvanian and the underlying Devonian. The latter is represented by the Mount Pleasant red shale of the continental Catskill facies to the east and the youngest marine Devonian, the Oswayo formation, to the west. The marine Mississippian consists of the Knapp formation including the Kushequa shale and Marvin Creek “limestone”. The Knapp is largely composed of sandstones and conglomerates, the latter distinguished by their discoidal, milky quartz pebbles and occasionally a jasper phenoclast. The marine Mississippian yields Kinderhook fossils. The continental Mississippian, carrying the Triphyllopteris flora, consists of the gray Pocono sandstones and pebble beds which to the east are overlain by the Mauch Chunk red shale, not recognized in north-central Pennsylvania. In the region of marine-continental transition, the Mississippian system is represented by approximately 150 feet of beds. The marine fossils gradually disappear eastward as the discoidal-pebble conglomerates and sandstones of the Knapp merge with the Pocono sandstone and conglomerate.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.

Marine Jurassic Formations of Sweetgrass Arch, Montana

The marine Jurassic rocks of the Sweetgrass arch in western north-central Montana have been assigned to the Ellis formation. As a result of measuring and sampling eleven Jurassic sections around the Sweetgrass arch and from examining numerous well cuttings, the writer concludes that the Ellis consists of three major lithologic divisions that should be recognized as formations, and that the Ellis should be raised to group rank. The formations of the Ellis group from oldest to youngest are herein named Sawtooth, Rierdon, and Swift. The Sawtooth formation consists of three members, a basal fine-grained sandstone, a medial dark gray shale containing a few dark limestone beds, and an upper member of light gray calcareous siltstone, fine-grained sandstone, or sandy, oolitic limestone. The Sawtooth is as little as 8 feet in thickness on the Kevin-Sunburst dome. It thickens eastward to 200 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The lower two members pass into redbeds east of the Sweetgrass Hills and on the southeast flank of the South arch. The Rierdon formation consists mainly of gray limy shale and nodular limestone. It seems to overlie the Sawtooth formation conformably. It is as little as 72 feet in thickness on the Kevin-Sunburst dome, but thickens eastward to 180 feet in the Sweetgrass Hills and westward to about 200 feet along the Rocky Mountain Front. The formation is absent over most of the South arch. The Swift formation is composed of two members along the Rocky Mountain Front and eastward across the Kevin-Sunburst dome at least as far as the Sweetgrass Hills. The lower member is dark non-calcareous shale, highly glauconitic at the base. The upper member is gray fine-grained flaggy glauconitic sandstone containing abundant black-gray micaceous shale partings. On the South arch the formation consists of fine-grained flaggy sandstone which is locally pebbly at the base. In the vicinity of the Little Belt Mountains the formation is massive fine-grained sandstone containing a prominent basal conglomerate. The Swift attains its maximum thickness of 166 feet in the Pondera field. The formation has been removed by pre-Kootenai erosion from most of the Cut Bank area, and from a small area west of the Whitlash field. All the formations are fossiliferous. According to Imlay, the Sawtooth is upper Bathonian, the Rierdon is upper Bathonian and Callovian, and the Swift is Divesian and Argovian. The South arch was an island through most of the Bathonian and Callovian stages. At the close of the Callovian the marine waters retreated from the area. During the early Divesian the Sawtooth and Rierdon formations were locally thinned by erosion and possibly removed from some areas. Later in the Divesian marine waters transgressed the entire area and remained until the close of the Argovian.

Reconsideration of the Morrison formation in the type area, Jefferson County, Colorado

The section of the Morrison formation recommended as the “type” has been selected because the entire Morrison is exposed along the West Alameda Parkway road cut, 2 miles north from Morrison, Colorado, and because the locality is readily accessible. The Morrison formation at the recommended type section is a distinct cartographic unit which can be subdivided into six parts primarily on the basis of lithologic characteristics of the sedimentary rocks. Fossils in this section of the Morrison formation are confined to three horizons. Dinosaur remains occur in limited number in basal sandstones of the gray shale and sandstone unit. Probable fresh-water sponge spicules are plentiful throughout an interval of 25 feet in the central part of the gray clay and limestone unit. A few spicules, however, are also present from 2 to 6 feet above the dinosaur-bearing sandstone. Aclistochara , the occurrence of which has not been mentioned previously in literature on the Morrison formation in Colorado, is relatively abundant in the upper 30 feet of the gray and red shale unit. This would place the highest occurrence of Aclistochara 63 feet above the base of the Morrison formation. The results of copper nitrate staining of samples from the calcareous rocks of the Morrison formation indicate that the greatest amount of calcite is present in the gray clay and limestone unit. In all probability the distribution and intensity of copper nitrate stains could be used effectively in connection with petrographic studies to identify several strata within the formation.