Lawrence Formation Research Articles

Morphology, variation, and systematics of the late Cambrian Laurentian dikelocephalid trilobiteWalcottaspis vanhornei(Walcott, 1914)

AbstractWalcottaspis vanhornei(Walcott, 1914) is a large, late Cambrian trilobite with a unique pygidial morphology known only from a narrow outcrop belt of the St. Lawrence Formation in the Upper Mississippi Valley. Found in carbonate-rich layers within heterolithic facies that represent the toesets of a prograding shoreface, it is restricted to a single or small number of parasequences. Only four specimens of any of its sclerites have been illustrated previously. Here holaspid examples of all its biomineralized sclerites are described and illustrated, along with a morphometric analysis of cranidial landmarks and landmarks plus semilandmarks for the pygidium. Ontogenetic allometry accounts for 29% of the variance among holaspid cranidia and includes a relative shortening and narrowing of the palpebral lobe and a reduction in the relative length and width of the frontal area. Notable pygidial phenotypic variation occurs in the extent of the postaxial region and in the proportion of the structure occupied by the axis. Phylogenetic analysis suggests thatW. vanhorneiis sister taxon toDikelocephalus minnesotensisOwen, 1852, which also occurs in the St. Lawrence Formation and has a broadly similar cephalon but distinctive trunk. The holaspid pygidium ofW. vanhorneiis uniquely characterized by the interpleural furrows of the first two segments becoming abruptly obsolete on approaching the axial furrow. Some pygidia show narrow, shallow, flat-bottomed grooves etched into the internal sides of the dorsal surface or doublure that apparently represent infestation of the live trilobite.

Carboniferous horseshoe crab musculature suggests anatomical conservatism within Xiphosurida

AbstractAn exceptionally preserved specimen of the horseshoe crab Euproops danae (Xiphosurida, Belinurina) in a siderite concretion from the Carboniferous (Upper Pennsylvanian, Virgilian) Lawrence Formation, Kansas, shows anatomical details of the prosomal musculature. The extrinsic appendicular muscles are comparable to those of Limulus polyphemus (the modern American horseshoe crab), demonstrating anatomical conservatism within Xiphosurida that spans two morphologically disparate subgroups, Belinurina and Limulina. The three‐dimensional preservation of muscles highlights how siderite concretion fossils (including those of the Mazon Creek Konservat‐Lagerstätte) have better preservational fidelity than previously realized and the potential to reveal new anatomical information, especially with regard to the labile tissues of euarthropods.

A multidisciplinary-based conceptual model of a fractured sedimentary bedrock aquitard: improved prediction of aquitard integrity

A hydrogeologic conceptual model that improves understanding of variability in aquitard integrity is presented for a fractured sedimentary bedrock unit in the Cambrian-Ordovician aquifer system of midcontinent North America. The model is derived from multiple studies on the siliciclastic St. Lawrence Formation and adjacent strata across a range of scales and geologic conditions. These studies employed multidisciplinary techniques including borehole flowmeter logging, high-resolution depth-discrete multilevel well monitoring, fracture stratigraphy, fluorescent dye tracing, and three-dimensional (3D) distribution of anthropogenic tracers regionally. The paper documents a bulk aquitard that is highly anisotropic because of poor connectivity of vertical fractures across matrix with low permeability, but with ubiquitous bed parallel partings. The partings provide high bulk horizontal hydraulic conductivity, analogous to aquifers in the system, while multiple preferential termination horizons of vertical fractures serve as discrete low vertical hydraulic conductivity intervals inhibiting vertical flow. The aquitard has substantial variability in its ability to protect underlying groundwater from contamination. Across widespread areas where the aquitard is deeply buried by younger bedrock, preferential termination horizons provide for high aquitard integrity (i.e. protection). Protection is diminished close to incised valleys where stress release and weathering has enhanced secondary pore development, including better connection of fractures across these horizons. These conditions, along with higher hydraulic head gradients in the same areas and more complex 3D flow where the aquitard is variably incised, allow for more substantial transport to deeper aquifers. The conceptual model likely applies to other fractured sedimentary bedrock aquitards within and outside of this region.

Karst conduit flow in the Cambrian St. Lawrence Confining Unit, southeast Minnesota, USA

Southeastern Minnesota’s karst lands support numerous trout streams created by Paleozoic bedrock springs. Several of the Paleozoic bedrock units are recognized as karst aquifers. Recent field investigations have discovered sinking, and one losing, streams in the Cambrian St. Lawrence Formation. The siliciclastic-dominated St. Lawrence Formation has historically been viewed as a confining unit and is designated as such in the Minnesota Water Well Code. Stream sinks in the St. Lawrence Formation have been identified in five different streams, and there are numerous other streams crossing the St. Lawrence that have yet to be investigated. Dye traces have been conducted on the five streams. At all of the sites, dye was recovered at springs emanating from the base of the St. Lawrence Formation. The initial dye breakthrough occurs quickly, but the breakthrough curves have tails that continue for months to over a year. Breakthrough travel velocities from the sinks to the springs are 35–750 m/day. The five dye tracing sites are geographically separated by 65 km. The subcrop of the St. Lawrence Formation is found throughout southeastern Minnesota and southwestern Wisconsin. The St. Lawrence Formation has well-developed macroporosity; most of the formation is moderately to well cemented with dolomite and contains abundant horizontal and vertical fractures in outcrop and subcrop conditions. Volumetrically minor dolomite beds with centimeter-scale solution cavities are common in the lowermost part of the formation. These attributes, combined with rapid groundwater flow as determined by dye tracing, supports the conclusion that this purported confining unit has karst conduit flow properties in subcrop conditions.

Three-dimensionally preserved arthropods from Cambrian Lagerstätten of Quebec and Wisconsin

Three new types of arthropod are described from Cambrian intertidal lithofacies of the Elk Mound Group and St. Lawrence Formation of Wisconsin and the Potsdam Group of Quebec. These arthropods are preserved ventrally in sandstone in life position and in three dimensions, allowing detailed characterization of limb morphologies, labrums, and other organs such as eyes. A taphonomic model is presented, illustrating this unusual, uncompressed, three-dimensional style of preservation.Arenosicaris inflatan. sp., from the Terreneuvian-Furongian Elk Mound Group and the Furongian St. Lawrence Formation, is the earliest unambiguous occurrence of a malacostracan phyllocarid. This 3 cm long arthropod had ovate valves, five pairs of biramous pleopods, and at least 3 pairs of thoracopods.Mosinieia macnaughtonin. sp., a large (>10 cm long) euthycarcinoid of uncertain affinity with flattened or paddle-like appendages also occurs in Elk Mound strata.Mictomerus melochevillensisn. sp. represents a new euthycarcinoid family and is the first known non-trilobite arthropod from the middle Cambrian-Furongian Potsdam Group of Quebec.M. melochevillensisn. sp. is large (8–10+ cm long), with as many as eleven pairs of well-preserved homopodous, uniramous, non-paddle-like limbs. BothM. macnaughtoniandM. melochevillensisdiffer substantially from previously known euthycarcinoids in limb morphology and represent the oldest known representatives of the group. Additionally, bothM. melochevillensisn. sp. andM. macnaughtonin. sp. possess morphologies that are consistent with abundant subaerial and subaqueousDiplichnitesandProtichnitestrackways known from these units, suggesting that these may be the earliest land-going animals.

Three-dimensionally preserved arthropods from Cambrian Lagerstätten of Quebec and Wisconsin

Three new types of arthropod are described from Cambrian intertidal lithofacies of the Elk Mound Group and St. Lawrence Formation of Wisconsin and the Potsdam Group of Quebec. These arthropods are preserved ventrally in sandstone in life position and in three dimensions, allowing detailed characterization of limb morphologies, labrums, and other organs such as eyes. A taphonomic model is presented, illustrating this unusual, uncompressed, three-dimensional style of preservation. Arenosicaris inflata n. sp., from the Terreneuvian-Furongian Elk Mound Group and the Furongian St. Lawrence Formation, is the earliest unambiguous occurrence of a malacostracan phyllocarid. This 3 cm long arthropod had ovate valves, five pairs of biramous pleopods, and at least 3 pairs of thoracopods. Mosinieia macnaughtoni n. sp., a large (>10 cm long) euthycarcinoid of uncertain affinity with flattened or paddle-like appendages also occurs in Elk Mound strata. Mictomerus melochevillensis n. sp. represents a new euthycarcinoid family and is the first known non-trilobite arthropod from the middle Cambrian-Furongian Potsdam Group of Quebec. M. melochevillensis n. sp. is large (8–10+ cm long), with as many as eleven pairs of well-preserved homopodous, uniramous, non-paddle-like limbs. Both M. macnaughtoni and M. melochevillensis differ substantially from previously known euthycarcinoids in limb morphology and represent the oldest known representatives of the group. Additionally, both M. melochevillensis n. sp. and M. macnaughtoni n. sp. possess morphologies that are consistent with abundant subaerial and subaqueous Diplichnites and Protichnites trackways known from these units, suggesting that these may be the earliest land-going animals.

Channels Ran Through It—The Lawrence Formation at Lone Star Lake, Douglas County, Kansas

The upper part of the Ireland Sandstone Member of the Lawrence Formation exposed in the spillway of Lone Star Lake, southwest of Lawrence, Kansas, consists of abundant pinstripe-bedded shales and siltstones; thin, lenticular sandstone and siltstone beds; and meter-scale, channel-form sandstone and mudstone lenses. Soft-sediment-deformation structures, including load casts, ball-and-pillow, and pseudonodules are abundant. The lenticular and pinstripe bedding with bipolar paleocurrents suggests tide-influenced deposition. The crosscutting, channel-form deposits are interpreted as tidal channels in an environment with low energy but rapid sedimentation. The depositional environment was a tide-dominated, muddy upper estuary cut by tidal channels. Gravitational instabilities resulting from rapid deposition of sand over saturated mud produced inverse-density gradients that resulted in soft-sediment deformation.

ABSTRACT: The Early Cenozoic Tectonostratigraphic Evolution and Sedimentology of the Judge Daly Basin, northeastern Ellesmere Island, Canadian High Arctic

The early Cenozoic evolution of the Canadian High Arctic was governed by a compressional stress regime related to the opening of Baffin Bay-Labrador Sea. On northeastern Ellesmere Island, the Eureka Sound Group sediments (late Paleocene in age) record the paleogeographic reorganisation of this event. This group is divisible into three formations and are preserved within six outliers in this area. The oldest of these units, the Mokka Fiord Formation is characterised by a brown weathering medium - to coarse grained lithic sandstone occuring as decimeter scale trough cross bedded units. These sediments are to 740 metres thick and are interpreted to be a predominantly fluvial deposit. The overlying and younger Cape Back Formation is interpreted to be fluviolacustrine in origin consisting of interbedded fine grained litho- to calcarenite, siltstone, and mudrock. Current ripples, climbing ripples, ripple and parallel laminations are common throughout this formation which reaches a total thickness of 1100 metres. Polymictic boulder orthoconglomerates of the Cape Lawrence Formation varies in thickness from 700 to 1000 metres. Clast composition consists of a variety of siliciclastics and carbonates. These conglomerate units are interpreted to be proximal gravely rivers which were alluvial fans. These data provide us with a valuable contribution towards advancing our understanding of the dynamics of this syntectonic siliciclastic depositional system.

The Relationship Between Geology and Landslide Hazards of Atchison, Kansas, and Vicinity

Landslides along the Missouri and Kansas rivers will affect existing structures and potential development in the Kansas City metropolitan area. A pilot landslide-mapping project was conducted in the vicinity of Atchison, Kansas, to inventory existing landslides and determine the factors that caused them. Landslides are generally controlled by the slope morphology, geology, soils, and moisture conditions. For this study, landslides were divided into recent and older landslides (including earth slides and earth flows) and rock-fall hazards (including rock falls and rock topples). Recent landslides are associated with shale members of the Pennsylvanian Lawrence Formation, Oread Limestone, Kanwaka Shale, and Tecumseh Shale. Limestone layers that occur between these shale members were incorporated into recent and older landslides. Recent landslides occurred on slopes with an average angle of 22 degrees. Recent landslides were also observed in glacial drift, loess, and alluvium. Rock-fall hazards occurred in areas of nearly vertical slopes along streams, river bluffs, highways, and quarries, where limestone members of the Pennsylvanian Oread, Lecompton, and Deer Creek Limestones are exposed. Troublesome rock-fall hazards occurred where weak shale layers are eroding underneath resistant limestone layers.

LATE CAMBRIAN CONULARIIDS FROM WISCONSIN AND MINNESOTA

Several localities within the heterolithic facies of the St. Lawrence Formation (Upper Cambrian) of Wisconsin and Minnesota yield specimens with phosphatic exoskeletons, quadrate cross sections composed of four equidimensional faces each bearing a midline, and possible holdfast attachment during life. These specimens are here referred to the order Conulariida, class Scyphozoa. Their fine, tuberculate surface ornament and serially invaginated midline structure serve to define a new genus, Baccaconularia, to which two new species, B. robinsoni and B. meyeri, are assigned. Conularia cambria Walcott 1890, also from the Cambrian of the northern Mississippi Valley and long dismissed as a misidentified trilobite fragment, is illustrated photographically for the first time. This species occurs in rocks stratigraphically beneath the St. Lawrence Formation. Specimens assigned to this species by Walcott are conulariids, but lack features now considered diagnostic of either Conularia or Baccaconularia. Walcott's material is insufficient to permit detailed taxonomic evaluation, and we isolate this name to this material, pending the collection of additional, better preserved specimens. Together, Baccaconularia and Conularia cambria contain the oldest large conulariids, and these narrow a stratigraphic gap between other large conulariids known from the Lower Ordovician onwards, and smaller fossils with conulariid affinities known only from Lower Cambrian rocks.

Late Cambrian conulariids from Wisconsin and Minnesota

Several localities within the heterolithic facies of the St. Lawrence Formation (Upper Cambrian) of Wisconsin and Minnesota yield specimens with phosphatic exoskeletons, quadrate cross sections composed of four equidimensional faces each bearing a midline, and possible holdfast attachment during life. These specimens are here referred to the order Conulariida, class Scyphozoa. Their fine, tuberculate surface ornament and serially invaginated midline structure serve to define a new genus, Baccaconularia, to which two new species, B. robinsoni and B. meyeri, are assigned. Conularia cambria Walcott 1890, also from the Cambrian of the northern Mississippi Valley and long dismissed as a misidentified trilobite fragment, is illustrated photographically for the first time. This species occurs in rocks stratigraphically beneath the St. Lawrence Formation. Specimens assigned to this species by Walcott are conulariids, but lack features now considered diagnostic of either Conularia or Baccaconularia. Walcott's material is insufficient to permit detailed taxonomic evaluation, and we isolate this name to this material, pending the collection of additional, better preserved specimens. Together, Baccaconularia and Conularia cambria contain the oldest large conulariids, and these narrow a stratigraphic gap between other large conulariids known from the Lower Ordovician onwards, and smaller fossils with conulariid affinities known only from Lower Cambrian rocks.

Horseshoe Crabs (Arthropoda: Xiphosurida) from the Pennsylvanian of Kansas and Elsewhere

Pennsylvanian strata of Kansas have yielded two species of xiphosurids (horseshoe crabs). The exceptionally preserved fossils are from inferred coastal (estuarine or tidal flat) paleoenvironments. One species, the euproopid Euproops danae (Meek and Worthen), occurs in the Lawrence Formation (Upper Pennsylvanian: Virgilian) in Douglas County, Kansas. Siderite concretions in the Lawrence Formation preserve organisms similar to those from Braidwood-type assemblages of the Mazon Creek biota of Illinois. This occurrence of E. danae in the Virgilian Stage (North American usage) is one of the few stratigraphically above the Desmoinesian Stage of North America or the Westphalian D Series of Europe. Another xiphosurid, the limuline Paleolimulus signatus (Beecher), occurs in the Pony Creek Shale Member of the Wood Siding Formation (Upper Pennsylvanian: Virgilian) in Wabaunsee County, Kansas. This occurrence extends the known stratigraphic range of P. signatus downward from the Permian into the Pennsylvanian. Another specimen that is here referred to P. signatus, and which was collected from the Mazon Creek biota of Illinois, shows that the species ranges downward to the Desmoinesian Stage (of North American usage).

Paleosol in Galesburg Formation (Kansas City Group, Upper Pennsylvanian), northern Midcontinent, U.S.A.; evidence for climate change and mechanisms of marine transgression

ABSTRACT A widespread paleosol in the Galesburg Formation (Kansas City Group, Missourian) in the northern Midcontinent Upper Pennsylvanian cyclothem (MUPC) outcrop belt exhibits prominent features, including repeating sets of synformal slickensides and mukkara or chimney structures, which characterize it as a paleo-Vertisol. The Galesburg paleosol has pervasive low-chroma grayish to greenish coloration, an organic-matter profile, and geochemical characteristics with regard to S, Fe2O3, MnO, SiO2, and Al2O3 that indicate wetter soil conditions than those indicated by equally widespread high-chroma paleosols higher in the local stratigraphic succession (particularly a high-chroma paleo-Vertisol in the upper Lawrence Formation). The predominance of low-chroma (i.e., wetter) paleosols throughout the Kansas City Group in the northern Forest City Basin (southeastern Nebraska and southwestern Iowa), as exemplified by the Galesburg paleosol, compared to the greater frequency of high-chroma (i.e., drier) paleosols in overlying Pennsylvanian (especially Virgilian) strata, implicates decreasing rainfall in the interior of North America during the late Missourian. The variability in rainfall through this Missourian-Virgilian shift need not have exceeded the range of rainfall (400-1400 mm/a) associated with modern soil analogs in subtropical to warm-temperate North America. Thus, there is an indication of climate change on a longer-term time scale ( 105-106 a) than the intra- or inter-eustatic-cycle climate change proposed by other authors for late Paleozoic cyclothems in the North American interior. Regional differences in the nature of transgressive marine strata directly above the Galesburg further suggest: (1) that important information relevant to reconstruction of the sea-level curve is probably missing from the interval between regressive paleosols and subsequent regressive limestones in MUPCs, and (2) that there were probably appreciable differences in the overall mechanism of deposition of MUPC transgressive shales and black core shales within any particular interval of MUPC transgressive deposition.

Virgilian (Upper Pennsylvanian) Paleosols in the upper Lawrence Formation (Douglas Group) and in the Snyderville Shale Member (Oread Formation, Shawnee Group) of the northern Midcontinent, USA; pedologic contrasts in a cyclothem sequence; discussion and reply

Virgilian (Upper Pennsylvanian) Paleosols in the upper Lawrence Formation (Douglas Group) and in the Snyderville Shale Member (Oread Formation, Shawnee Group) of the northern Midcontinent, USA; pedologic contrasts in a cyclothem sequence; discussion and reply

Virgilian (Upper Pennsylvanian) Paleosols in the Upper Lawrence Formation (Douglas Group) and in the Snyderville Shale Member (Oread Formation, Shawnee Group) of the Northern Midcontinent, USA: Pedologic Contrasts in a Cyclothem Sequence: REPLY

Virgilian (Upper Pennsylvanian) Paleosols in the Upper Lawrence Formation (Douglas Group) and in the Snyderville Shale Member (Oread Formation, Shawnee Group) of the Northern Midcontinent, USA: Pedologic Contrasts in a Cyclothem Sequence: REPLY

Virgilian (Upper Pennsylvanian) Paleosols in the upper Lawrence Formation (Douglas Group) and its Snyderville Shale Member (Oread Formation, Shawnee Group) of the northern Midcontinent, USA; pedologic contrasts in a cyclothem sequence

ABSTRACT Paleosols in the upper Lawrence Formation and in the Snyderville Shale Member (Virgilian) extend over an estimated area of over 14,000 km2 in Nebraska, Iowa, Missouri, and Kansas. These paleosols, both within cyclothems, are: (1) critical indicators of nearly basin wide emergence (peak regression of the Midcontinent seaway) and geomorphic stability, and (2) useful stratigraphic markers. Both paleosols appear to be analogous to modern Vertisols: they have nested, synformal-antiformal sets ( 4-10 m wide) of very large, intersecting slickensides. Also, some profiles of the upper Lawrence paleosol also have filled cracks extending to depths of 100+ cm. There are, however, significant differences between the paleosols: high-chrom coloration, strong preserved soil structure, and small iron oxide nodules (upper Lawrence) versus dominantly low-chroma coloration, weak to very weak preserved soil structure, and pyrite segregations (Snyderville). After a period of widespread subaerial exposure, each paleosol was drowned and slightly eroded by a marine transgression. The upper Lawrence shows a single paleosol across the study area. The paleosol is thickest and best-developed shelfward (northward) and shows topohydrosequence variation at two basinward localities in northeastern Kansas. Stratigraphic trends suggest an appreciable time differential in the south-to-north migration of the Toronto transgression. The Snyderville shows two welded paleosols in southeastern Nebraska and a single one elsewhere in the study area. Elsewhere in the Snyderville, there is local evidence for lowstand incision of streams and small lows that underwent little or no subaerial exposure. Snyderville paleogeography and pedogenesis, however, were markedly different from upper Lawrence paleogeography and pedogenesis. Contrasts between the two paleosols are likely to be rel ted to intercycle changes in geomorphic conditions (driven by patterns of sedimentation, eustasy, and tectonics) and climate.

Aglaspidida (Arthropoda) from the Upper Cambrian of Wisconsin

New specimens of aglaspidid arthropods, mainly from the Upper Cambrian St. Lawrence Formation of Wisconsin (UpperDikelocephalusZone), show that appendages previously assigned to the genotypeAglaspis barrandeiactually belong to a new genus and speciesFlobertia kochi. Chraspedops fragilisis transferred to a new genusTuboculops. The generic attribution ofAglaspis dorsetensisandAglaspis franconensisis queried. The distinction at species level is queried forSetaspis spinulosusandS. regularisand also forAglaspoides sculptilisandA. semicircularis, although no formal changes are recommended.Aglaspis simplexis transferred toGlypharthrus simplexandGlypharthrus deadwoodensisis synonymized withGlypharthrus vulpes. Restorations are presented ofAglaspis barrandei, Aglaspis spinifer, andGlypharthrus thomasi. Aglaspis spiniferprobably had a total of four head appendages. Well-preserved aglaspidid specimens often evince tergal processes that are apparently unique to this taxon and these may have acted as apodemes.

Vertebrate Fossils from the Lawrence Formation (Douglas Group, Virgilian, Upper Pennsylvanian) in Northeastern Kansas

Vertebrate Fossils from the Lawrence Formation (Douglas Group, Virgilian, Upper Pennsylvanian) in Northeastern Kansas

Trace fossils of Cambrian aglaspidid arthropods

A new trace fossil, Raaschichnus gundersoni, from the Upper Cambrian St. Lawrence Formation of Wisconsin, was produced by an aglaspidid arthropod. The rusophyciform trace, which occurs singly and in series, is distinctive in showing marks left by the tail-spine. Other trace fossils previously considered to have been made by aglaspidids were probably excavated by animals lacking a tail-spine and with appendage morphologies very different from the aglaspidids of Wisconsin.

Cambrian Lithostratigraphy of Michigan Basin

The composite Cambrian sequence of the Lower Peninsula of Michigan consists, in ascending order, of the Mt. Simon Sandstone; Munising Group, composed of the Eau Claire Formation, Galesville Sandstone, and Franconia Formation; St. Lawrence Formation; Lodi Formation (a minor unit); and the Jordan Sandstone. They compose an estimated 3,000 ft (915 m) of section at the approximate depocenter, near or possibly in Ogemaw County. These rocks long have been an enigma to Michigan geologists because of a lack of both drilling information and outcrops. When viewed against the broad, regional stratigraphic framework and defined rigorously in terms of lithology, they are clearly identifiable as representing sedimentary facies deposited in or near the margins of a transgressive-regressive sea. The Mt. Simon Sandstone represents the high-energy shoreline facies of the northerly transgressing Cambrian sea. The glauconitic Eau Claire and Franconia Formations of the Munising Group are composed of sandstone, siltstone, and minor dolomite and shale interbeds which reflect a lower energy, near-shore marine environment. These two units can be distinguished from one another only where separated by the Galesville Sandstone, a regressive unit restricted to southern and western Michigan. Outside the depositional limits of the Galesville, there is present within the Munising Formation interbedded sandstone, dolomite, shale, and nodular anhydrite which, taken together, strongly suggest a shallow to supratidal environment of deposition. Known only in central Michigan, the areal extent of his facies is undetermined. Essentially a dolomite unit, the St. Lawrence Formation contains many chert and cherty sandstone interbeds in southwestern and western Michigan. The term St. Lawrence includes those stratigraphic elements called Trempealeau and Prairie du Chien in previous investigations. The St. Lawrence grades upward into the Jordan Sandstone, a regressive sandstone unit that documents the gradual infilling of the Michigan basin area. The Jordan Sandstone has been identified erroneously in prior reports as the St. Peter Sandstone of the Mid-Continent region, but the St. Peter was not recognized anywhere within the area of study. The top of the section is bounded by an erosional unconformity of regional extent on which rocks of the Glenwood Formation (Middle Ordovician) were deposited. The Mt. Simon through Jordan rocks form an essentially continuous sequence of deposition beginning with marine transgression probably in the Late Cambrian and ending with regression and regional uplift in the Early Ordovician. The sedimentary record clearly places the formation of the Michigan basin back at least to Late Cambrian time. In the light of the growing energy crisis in the United States, the clarification of the stratigraphic relations of these rocks should lead to increased interest in their petroleum potential.