Gun River Research Articles

Evolution and drivers of secondary suspended rivers in typical wandering sections of the lower Yellow River from 1960–2021

The secondary suspended river increases the probability of the occurrence of “Heng river”, “Xie river” and “Gun river” in the lower Yellow River, and is the main factor threatening the safety of human life and property in the Yellow River levee and beach area. Here, the Dongbatou–Gaocun section of the severe secondary suspended river in the lower Yellow River was taken as the research object. The trend and periodicity of the evolution characteristics of the secondary suspended river in the study area from 1960–2021 were systematically analyzed using the Theil-Sen estimator and wavelet analysis, and the factors influencing its development were quantitatively explored. Over the past 62 years, development of secondary suspended rivers can be divided into four stages: initial formation (1960–1973), slow development (1974–1986), rapid development (1987–1999) and stable (2000–2021) periods. The evolution period of the beach transverse gradient differed significantly before and after operation of Xiaolangdi Reservoir commenced, prior to which there was a first main period of 31 years followed by a second main period of 21 years. Development of secondary suspended rivers was primarily related to floodplain flooding and human activity. When the inflow sediment coefficient of a floodplain flood (ζ) was < 0.04 and the floodplain coefficient was < 1.29, the secondary suspended river was relieved; when ζ > 0.04 or ζ < 0.04 and the floodplain coefficient was > 1.29, the secondary suspended river was intensified. The production levees have exacerbated development of secondary suspended rivers to some extent.

Early athyride brachiopod evolution through the Ordovician-Silurian mass extinction and recovery, Anticosti Island, eastern Canada

AbstractThe subfamily Hindellinae is an early group of athyride brachiopods, characterized by a simple jugum that connects the laterally directed spiralia, which are disjunct from the crura. Four genera (Hindella,Cryptothyrella,Koigia, andHyattidina) are reexamined on the basis of their internal structures, such as the crura and their connection to the hinge, the jugum, and spiralia. The internal brachidium and shell of the Aeronian genusCryptothyrelladiffer substantially from those ofHindella.Elkanathyris pallulan. gen. n. sp. is recognized as a posteriorly ribbed hindellide of Aeronian age. These genera are transferred from the Meristellinae to the subfamily Hindellinae (family Hindellidae). On Anticosti Island,Hindellais confined to the Hirnantian (latest Ordovician): it became extinct at the end Ordovician during the last of several mass extinction events that also extinguished the Laframboise reefs at the top of the Ellis Bay Formation. Post-extinction recovery of athyrides was pioneered by small-shelledKoigia, which are abundant in the basal Silurian Becscie Formation.Hyattidina, with a simple brachidium, is abundant in the Aeronian and Telychian of Anticosti, but absent earlier. True meristellines, as envisioned here, first appeared in the Aeronian Gun River Formation. The revised taxonomy and stratigraphic ranges of these earliest athyrides shed light on the nature of the Ordovician–Silurian mass extinction and recovery, and help refine the biostratigraphy of the O-S boundary interval.

A New Noncalcified Thallophytic Alga from the Lower Silurian of Anticosti Island, Eastern Canada

An exceptionally preserved noncalcified thallophytic alga, Menieria minuta gen. nov. et sp. nov. from the uppermost Gun River Formation (middle Aeronian, Lower Silurian) of Anticosti Island, eastern Canada, is characterized by a relatively delicate thallus with a central axis, lateral branches, and helically arranged, regularly and closely spaced, elongate-linguoid appendages. The algae locally constitute an important portion of the biomass in a brachiopod-dominated paleocommunity, forming an algal meadow on a relatively deepwater subtidal setting within the photic zone. This rare fossilization window suggests that such soft algal meadows may have been common during the Early Paleozoic, resembling modern sea grass meadows that are part of the carbon sink.

The Early Silurian Gun River Formation of Anticosti Island, eastern Canada: A key section for the mid-Llandovery of North America

The 85–100 m thick carbonate succession of the Gun River Formation is revised on the basis of nearly continuous cliff sections measured on the northeast coast, and a re-analysis and re-measurement of the stratotype sections on the southwest coast of Anticosti island, Quebec. The Gun River Formation (Llandovery: lower Aeronian) is herein formally divided into four members, from the base up, the Lachute, Innommee, Sandtop and Macgilvray members. The formation characterizes a generally deepening phase on the northwestern shelf of Laurentia, bordering the Iapetus ocean in this region. Since the base of the formation is located ca. 150 m above the O/S boundary, it provides fresh data as to the nature of the Early Silurian transgression, radiation, and re-invasion of shelf communities following the Late Ordovician mass extinctions. The Gun River strata were deposited in a midto distal, tropical, very gently sloping ( 1–3 m per km), carbonate ramp or shelf, some 40–80 km offshore from the stable Laurentian craton, and at water depths of 30 to 60 m. Much of the formation consists of rhythmically deposited, light grey micrites (with fissile muddy partings), and minor calcareous mudstones, punctuated by abundant hardgrounds, intraformational conglomerates, and shell-beds. The fauna of brachiopods and corals is generally of low diversity, marking a turnover from a latest Rhuddanian community (Merrimack–lower Gun River Fm) to a more diverse midAeronian fauna (top Gun River–lower Menier Fms) when large pentamerids become abundant. This indicates gradual changes rather than abrupt invasions, sustained deposition, and lack of major sedimentary gaps between stratigraphic units. The absence of shallow water reefs, skeletal stromatolites, and ooid or oncoid shoals, also suggests deposition near or periodically below the storm wave base on a carbonate platform in southern tropical latitudes at 20°–25° S.

Llandovery (Early Silurian) orthide brachiopod associations from Anticosti Island, eastern CanadaThis article is one of a series of papers published in this Special Issue on the theme The dynamic reef and shelly communities of the Paleozoic. This Special is in honour of our colleague and friend Paul Copper.

Five Llandovery orthide brachiopod associations, through cluster analysis, are delineated on Anticosti Island. The Levenea – Dicoelosia Association (A), occurring in the Goéland and Richardson members of the lower Jupiter Formation, represents a deep-water setting around or below the maximum storm wave base. The Flabellitesia – Dalejina Association (B), appearing in the Cybèle, Ferrum, and Pavillon members of the upper Jupiter Formation, indicates water depth in between the maximum and normal storm wave bases. The Isorthis ( Ovalella ) Association (C1), present in the Fox Point Member of Becscie Formation, corresponds to the shallower water setting around the normal storm wave base. The Mendacella bleikeriensis Association (C2), occurring in the Innommée, Sandtop, and Macgilvray members of Gun River Formation, characterizes the water depth slightly below the normal storm wave base. The Mendacella udauberis Association (D), appearing in the Merrimack Formation, signifies a water depth around the maximum storm wave base. The water depth indication of these associations may bear potential as future reference for other regions, but attention should be paid to the species level as some congeneric species can belong to different associations of different depth. The cluster analysis on orthide collections based on binary data demonstrates that statistical methods, Jaccard coefficient and Ward’s method of clustering, are practical and effective to delineate large brachiopod collections on Anticosti Island.

Late Ordovician - Early Silurian cryptospore occurrences on Anticosti Island (Île d'Anticosti), Quebec, Canada

Residues from Hirnantian (Upper Ordovician) and Aeronian (Lower Silurian) strata of Anticosti Island, Quebec, Canada, have yielded the oldest occurrence of terrestrial-based palynomorphs (cryptospores) from eastern North America. A low-abundance, low-diversity cryptospore assemblage containing specimens of Pseudodyadospora, Velatitetras, and alete monads has been recovered from the Velleda Member of the Ellis Bay Formation (Upper Ordovician, Hirnantian). The Gun River Formation (Lower Silurian, Aeronian) contains a low-abundance, low-diversity assemblage composed of specimens of Velatitetras, Laevolcancis, and alete monads. The occurrence of these assemblages provides evidence for early land plants in this part of North America during the Late Ordovician and Early Silurian, and documents the existence of a terrestrial-based flora during and after the Saharan (Late Ordovician) glaciation.

The paradox of the global standard Late Ordovician–Early Silurian sea level curve: Evidence from conodont community analysis from both Canadian Arctic and Appalachian margins

Relative sea level fluctuations in the Late Ordovician–Early Silurian were largely driven by Gondwana deglaciation, three possible short-lived ice readvances, and the closure of the Iapetus Ocean. This study establishes and compares sea level events on the Canadian Arctic and Appalachian margins of Laurentia based on the pattern of conodont communities, and demonstrates that sea level events were not synchronous on the two margins. Conodont data were compared for a) the Arctic margin from the Cape Phillips Formation (Richmondian, Upper Ordovician through lower Sheinwoodian, Lower Silurian), Cornwallis Island, Canadian Arctic Islands, and b) the Appalachian margin from the upper Ellis Bay, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations (Richmondian, Upper Ordovician, Rhuddanian, Aeronian, and most of Telychian, Lower Silurian), Anticosti Island, Quebec. The pattern of Late Ordovician–Early Silurian conodont communities is established based on three cluster analyses on conodonts from Cornwallis Island (4967 specimens representing 54 species from 77 samples, Cape Phillips Formation) and Anticosti Island (1980 specimens representing 21 species from 25 samples, upper Ellis Bay Formation; 24,839 specimens representing 42 species from 123 samples, Becscie, Merrimack, Gun River, Jupiter and Chicotte formations). Overall, the sea level curves inferred from the distribution of the conodont communities from Cornwallis and Anticosti exhibit gradual and rapid oscillating patterns, respectively. Specifically, during the time interval of the latest Ordovician and the Early Silurian (Rhuddanian), the sea level behaved differently in these two regions: 1) during the latest Ordovician, conodont community changes show the different patterns in the two regions, which reflects a transgression on Cornwallis, but a regression on Anticosti; 2) during the earliest Rhuddanian, similar conodont communities arose in both regions, but they indicate a regression on Cornwallis and a transgression on Anticosti; 3) in the early Rhuddanian, these communities were replaced by a deeper water community on Cornwallis and a shallower water community on Anticosti, which suggest a transgression on Cornwallis and a regression on Anticosti; 4) a highstand drove out almost all conodonts from Anticosti by the end of Rhuddanian, which is not seen on Cornwallis; 5) a deep-water conodont community remained almost unchanged on Cornwallis from the late Rhuddanian to the early Aeronian, whereas a shallow water conodont community returned to Anticosti in the early Aeronian. However, the sea level dropped on both Cornwallis and Anticosti during the late Telychian, and the sea level curves show a similar pattern. The difference in the sea level pattern during the late Richmondian, Rhuddanian and Aeronian on both the northern and southern margins of Laurentia reflected by conodont communities is supported by the studies on Quaternary glaciation/deglaciation events, where the melting of an ice sheet was accompanied by sea level change but with variable regional isostatic effects that do not generate a uniform global eustatic signal.

Relationships between lithofacies belts and conodont faunas, Gun River Formation (Lower Silurian), Anticosti Island, Quebec: a statistical approach

Discriminant analysis of 80 samples from the Western Carbonate Platform Facies and the Eastern Transitional Carbonate–Siliciclastic Platform Facies of the Gun River Formation (Lower Silurian) on Anticosti Island, Quebec, indicates the degree to which different conodont communities were related to particular lithofacies. The statistical analysis reveals that during most of the Gun River Formation deposition, the conodont distributional pattern of the Western Carbonate Platform Facies and the Eastern Transitional Carbonate–Siliciclastic Platform Facies of the formation remained stable, and that the boundary of the two facies oscillated eastward and westward. The analysis indicates quantitatively that Icriodella deflecta had a nearshore environmental preference, whereas Rexroadus kentuckyensis tended to reside in offshore environments. These two species play the most important role in differentiating conodont communities and determining the relationship between conodont communities and lithofacies among all of the 22 species known from the Gun River Formation.

Paleoecology of Llandovery conodonts, Anticosti Island, Québec

Anticosti Island, Québec, has perhaps the most fossiliferous and complete Llandovery (Early Silurian) sequence in the world. The undeformed limestones are well exposed and yield extremely well preserved conodonts whose taxonomy and biostratigraphy has been studied in detail. In addition to documenting the general temporal and spatial distribution of Llandovery conodonts, a set of 107 conodont samples was taken from four cliff sections in the lower and upper Becscie, lower Gun River, and upper Jupiter formations. These samples were used to examine the relationship of conodont elements and communities with microfacies, and explore their change through time. Over 9300 conodonts elements were identified and subjected to cluster analysis. The sections comprise mainly the background sedimentation of lime mudstones, deposited in 30–100 m of water on a gentle ramp. These mudstones are variably affected by interbeds or channel fill deposits interpreted as tempestites. A pattern of evolving conodont communities is documented for the lime mudstone facies through time. Different communities are found in the tempestite deposits that do not suggest a reworking of the mudstones, but rather the importation of deeper offshore faunas during periods of storm surge onto the ramp. The tempestites contain the highest species diversity and show no evidence of reduced diversity through post-mortem selective sorting by the storms.

A NEW LLANDOVERY (EARLY SILURIAN) CONODONT BIOZONATION AND CONODONTS FROM THE BECSCIE, MERRIMACK, AND GUN RIVER FORMATIONS, ANTICOSTI ISLAND, QUÉBEC

Abstract An abundant conodont fauna was recovered from 202 samples taken from the Becscie, Merrimack, and Gun River formations of early Llandovery (Early Silurian) age on Anticosti Island, Quebec. From the collection of 22,409 identifiable specimens, 28 species and four associations representing 12 genera and one group of drepanodontiform elements are documented and their stratigraphic ranges established. One new genus, Rexroadus, is established for two species earlier assigned with question to Oulodus. New species described are Icriodella dicrana, Oulodus sigmoideus, Ozarkodina strena, and Pterospathodus? originalis. The fauna is dominated by species of Ozarkodina and Oulodus; many species have a first appearance that is slightly older than elsewhere suggesting that the Anticosti Basin may have been an important evolutionary radiative center in the early Silurian. There is a slow and progressive diversity increase in conodonts through this interval after the initial appearance of many new taxa in the bas...

Anticostiodus, a new multielement conodont genus from the Lower Silurian, Anticosti Island, Quebec

The multielement conodont genus, Anticostiodus new genus, is described based on discrete elements from the Lower Silurian (early Aeronian) Gun River Formation of Anticosti Island, Quebec. The apparatus includes pectiniform Pa, Pb, Pc and Pd elements and ramiform M, Sa, Sb and Sc elements. Two new species are included under the new genus, Anticostiodus fahraeusi (type species) and Anticostiodus boltoni. Both species occur near the base of Distomodus staurognathoides Zone and in an open subtidal environment.

ANTICOSTIODUS,A NEW MULTIELEMENT CONODONT GENUS FROM THE LOWER SILURIAN, ANTICOSTI ISLAND, QUEBEC

The multielement conodont genus, Anticostiodus new genus, is described based on discrete elements from the Lower Silurian (early Aeronian) Gun River Formation of Anticosti Island, Quebec. The apparatus includes pectiniform Pa, Pb, Pc and Pd elements and ramiform M, Sa, Sb and Sc elements. Two new species are included under the new genus, Anticostiodus fahraeusi (type species) and Anticostiodus boltoni. Both species occur near the base of Distomodus staurognathoides Zone and in an open subtidal environment.

Kulumbella and Microcardinalia (Chiastodoca) new subgenus, Early Silurian divaricate stricklandiid brachiopods from Anticosti Island, eastern Canada

Ribbing became an increasingly common feature of pentamerid shells, especially the family Stricklandiidae, during the later Llandovery (Early Silurian). The thin shells of stricklandiids from the Llandovery (Aeronian-Telychian) equatorial carbonate rampshelf of Anticosti Island reveal at least three ribbing designs in various genera; 1) radially arranged ribs, e.g., Costistricklandia; 2) divergent, chevron-like ribs, e.g., Ehlersella; and 3) diagonally criss-cross, mutually intersecting divaricate ribs, as in Kulumbella and Microcardinalia (Chiastodoca) new subgenus. Weakly divaricate species previously assigned to Kulumbella, Stricklandia or Microcardinalia from Anticosti Island, South China and the Baltic region, are assigned to the new subgenus Chiastodoca (type Stricklandinia salterii Billings, 1868), and they are suggested to have evolved their divaricate ribbing from smooth forms, independently from the earlier genus Kulumbella, in the same sense that radial or divergent ribbing was developed separately in a number of pentamerid and stricklandiid lineages in the late Llandovery and Wenlock. In Anticosti, the divaricate genus Kulumbella, originally described from Siberia, appeared, without a known ancestral form, in the Anticosti Basin (as K. xacta n.sp.), and became extinct equally suddenly in the upper part of the Gun River Formation (mid-Aeronian). This sudden arrival of immigrant taxa, originally appearing earlier in other areas, is matched in other brachiopod groups and corals in the Anticosti section. Weakly divaricate ribbing in Chiastodoca is characteristic of the early Telychian (Ferrum Member, Jupiter Formation), and radial ribbing is typical of the late Telychian genus Costistricklandia (Pavillon Member, Jupiter Formation).

Reproduction and life strategies in the Paleozoic tabulate coral Paleofavosites capax (Billings)

Asexual and sexual modes of colony formation in a tabulate coral Paleofavosites capax are recognized from the early Silurian Gun River Formation of Anticosti Island. Québee. Colonies produced by asexual fragmentation comprise monospecific ‘clumped populations’. They are characterized by circular and concave bases, and lack a protocorallite origin of colony growth. Sexually produced colonies, where in situ, are always dispersed and characterized by conical bases with a definite protocorallite point origin of colony growth. Asexual colony formation by fragmentation in P. capax appears to have been an adaptation to a habitat of muddy substrates. Sexual reproduction in this species probably played a minor role but was necessary for the maintenance of gene diversity and long-distance dispersal. A comparison of corallite size distributions between populations demonstrates that intrapopulation variation in the ‘dispersed population’ and the conical colonies in ‘transported populations’ of P. capax is significantly larger than the variation in the ‘clumped populations’. It is suggested that this difference reflects the two modes of reproduction. The above observations are significant to systematic studies because they show that estimates of species morphologic parameters can he seriously biased even when based on a relatively large sample size from a well-defined population if that population is largely a result of asexual colony formation.

Evolution of the Early Silurian rhynchonellid brachiopodFenestrirostrain the Anticosti Basin of Quebec

Among the abundant, well-preserved rhynchonellid brachiopods in the Upper Ordovician–Lower Silurian rocks of Anticosti Island,FenestrirostraCooper, 1955, one of the earliest camarotoechiid genera to appear in the fossil record, is probably of oligorhynchiid ancestry and seemingly endemic to the Anticosti Basin. The genus differs most obviously from other camarotoechiids in its peculiar costae, which are angular and strong posteriorly and flat and weak anteriorly.Three successive species ofFenestrirostra, found in micritic mudstones and calcareous shales of the middle and upper Merrimack and Lower Gun River Formations, provide an example of gradualistic evolution. The most primitive species,F. primaeva, occurs only in the lower part of the middle Merrimack Formation; the descendant intermediate species,F. glacialis, occurs mainly in the upper part of the middle and in the upper Merrimack and in the lowermost Gun River Formations; and the descendant terminal species,F. pyrrha, occurs only in the lower Gun River Formation. Four major morphoseries distinguish the lineage: 1) change in the proportions and size of the shells; 2) increase in the number and concomitant loss of the costae from the anterior halves of the shells; 3) change in the orientation and reduction in the size of the hinge plates and hinge fossettes; and 4) change in the height of the median septum. The evolutionary modifications, estimated to have been accomplished in no more than 1 m.y., may have been adaptive responses to persistent low-energy marine conditions.Biostratigraphically, theFenestrirostralineage provides the basis for three interval or range zones that straddle the Rhuddanian–Aeronian interstage boundary in the Anticosti Basin.

Paleomagnetic study of the Late Ordovician–Early Silurian platform sequence of Anticosti Island, Quebec

Eighteen sites (152 samples, 441 specimens) from the Late Ordovician — Early Silurian sequence of Anticosti Island were studied paleomagnetically. Six sites were collected in the Vauréal Formation, seven in the Ellis Bay Formation, three in the Becscie Formation, and one each in the Gun River and Jupiter formations. The lithologies sampled consisted of limestones, sandy limestones, marls, and sandy calcareous shales drawn from a sedimentary platform sequence of predominantly inter-bedded limestones and shales. The specimens were demagnetized in alternating fields (AF) and thermally and were found to be quite stable. Two components of magnetization were isolated. The memory carrier is fine- to medium-grained magnetite; AF and thermal cleanings are about equally efficient. The average directions of residual magnetization are D = 167°, I = 37°, α95 = 18°; D = 315°, I = −24°, α95 = 17 °for components B and C, respectively. The corresponding paleopoles for the B and C components are 129°E, 19°N (dp = 12°, dm = 21°) and 341°E, 16°S (dp = 10°, dm = 18°).Component A is most probably composed of component C and the present Earth's field (PEF); it was chiefly observed in the more altered Vauréal Formation and in the altered top part of the cored samples. The most common component in the Ellis Bay, Becscie, Gun River, and Jupiter formations is component C. Component B is mainly found in the Becscie and Ellis Bay formations. Both components B and C are isolated in the 300–500 °C and 10–40 mT ranges. Component C is either older than component B or synchronous and of reverse polarity to component B. If this last alternative is correct, then the Ordovician and Silurian formations are overprinted by a pre-Kiaman magnetization. The more plausible scenario is the following: component B is secondary, of pre-Middle Carboniferous age, and overprinted on an older secondary magnetization (component C), the acquisition age of which is confined to the Silurian–Carboniferous time interval.

The heliolitid coralAcidolitesin Ordovician–Silurian rocks of eastern Canada

AcidolitesLang, Smith and Thomas occurs in upper Middle and Upper Ordovician, Lower and lower Middle Silurian rocks of Ontario and Quebec. On Anticosti Island, Quebec, the genus is represented byA. tenuis(Billings) in the Upper Ordovician (Gamachian) Ellis Bay Formation; the new speciesA. arctatus, A. compactusandA. helianthusin the Ordovician–Silurian boundary beds at the top of the Ellis Bay Formation; the new speciesA. arctatus, A. compactusandA. lindströmiin the lower Llandoverian Becscie Formation;A. arctatusin the mid-Llandoverian Gun River Formation; and an unnamed species in the upper Llandoverian Jupiter Formation. The lower Llandoverian Clemville Formation of the Gaspé Peninsula, Quebec, containsProtaraea clemvillensisParks, now considered to beAcidolites. The upper Middle to lower Upper Ordovician Cobourg Formation near Ottawa, Ontario, containsA. cf.arctatus, formerly included inProtaraea vetusta(Hall). The lower Wenlockian Amabel Formation in southern Ontario contains a species ofAcidolitesas yet unnamed.

Late Ordovician‐Early Silurian fluctuations in sea level from eastern Anticosti Island, Quebec

Over 1,000 m of Upper Ordovician to Lower Silurian mixed carbonate and clastic strata on Anticosti Island are nearly tectonically undisturbed, despite their proximity to the Northern Appalachians fronting Quebec's Gulf of St. Lawrence. Natural cliffs exposed along the coast and rivers in the eastern part of the island make a relatively conformable sequence belonging to the Ashgill and Llandovery Series. Fossil communities interpreted as depth-associated in life are especially repetitious in the Becscie, Gun River, Jupiter, and Chicotte Formations (Llandovery Series), and to a lesser degree in the Upper Vaureal and Ellis Bay Formations (Ashgill Series). Preliminary study of the pattern of changeovers in Eocoelia, Pentamerus and Stricklandia communities suggests that Anticosti seas deepened and shallowed three and a half times during the Early Silurian. High water peaks were reached during B1-B2, C1-C2 and C4-C5 times, with a final deepening trend beginning in late C5 time. Age determinations of these events are based on the occurrence of graptolites (with some new records from Anticosti) keyed to the standard graptolite zones, and species of the Eocoelia lineage are also useful for correlation. The profile of the Anticosti sea-level curve compares well with other curves reconstructed from the Lower Silurian of New York, Michigan, and Iowa. Widespread synchronism in sea-level changes on the North American platform is thus corroborated.

The Ordovician-Silurian Boundary in Britain and North America

The difficulties experienced in correlating strata near the Ordovician-Silurian boundary in Britain and North America arise partly from imperfect descriptions of the British Llandovery fauna. Many characteristic Llandovery fossils are attributed in lists to the Bala or Wenlock. In Britain, Ordovician and Silurian rocks occur in three fades: (1) pelitic, (2) psammitic, and (3) calcitic facies. The better-known American Ordovician and Silurian rocks belong mainly to the calcitic facies. A comparison is made between the genera of brachiopods and trilobites recorded from the British and American rocks near the Ordovician-Silurian boundary. In Anti-costi, the English Head, Charleton, and Ellis Bay must be referred to the Bala; the Becsie River is probably Lower Llandovery, while the Gun River, Jupiter River, and Chicotte are Upper Llandovery. The Richmond of the interior states is unmistakably Bala; the Clinton (and probably the Medina) is Upper Llandovery. Evidence that Lower Llandovery rocks occur on the American continent is wanting.