Pond Complex Research Articles

Microinvertebrate and plant beta diversity in dry soils of a semiarid agricultural wetland complex

The relationship between environmental features and the β diversity of the propagule bank of dry soils of temporary wetlands has relevance to ecological theories of community structure and to the conservation of wetland biodiversity. The correlation of β diversity of microinvertebrates and macrophytes derived from propagules in dry soils with wetland habitat characteristics, catchment land-use, and the distance between wetlands in a remnant pond complex in central Spain was assessed. Redundancy analyses showed that β diversity of both groups correlated with habitat characteristics, whereas associations with catchment agricultural practices were weaker. Nestedness analyses showed that species-poor communities from degraded sites tended to form nested subsets of less degraded ponds with higher species richness. Distance between the ponds had no significant association with community similarity, suggesting that fragmentation did not shape β diversity at the scale of our study area. To maintain high β diversity in this area, ponds with species-rich propagule banks should receive conservation priority. Given the functional dependence by much wildlife on these propagule banks once these wetlands rewet, conservation of this hidden biodiversity is crucial for providing ecosystem services to humans and wildlife.

How can we make new ponds biodiverse? A case study monitored over 7 years

A new pond complex, designed to enhance aquatic biodiversity, was monitored over a 7-year period. The Pinkhill Meadow site, located in grassland adjacent to the R. Thames, proved unusually rich in terms of its macrophyte, aquatic macroinvertebrate and wetland bird assemblages. In total, the 3.2 ha mosaic of ca. 40 permanent, semi-permanent and seasonal ponds and pools was colonized by approximately 20% of all UK wetland plant and macroinvertebrate species over the 7-year survey period. This included eight invertebrate species that are Nationally Scarce in the UK. The site supported three breeding species of wading bird and was used by an additional 54 species of waders, waterfowl and other wetland birds. The results from four monitoring ponds investigated in more detail showed that these ponds significantly supported more plant and macroinvertebrate species than both minimally impaired UK reference ponds, and other new ponds for which compatible data were available. Comparisons of the physico-chemical, hydrological and land-use characteristics of the Pinkhill pools with those of other new ponds showed that the site was unusual in having a high proportion of wetlands in the near surrounds. It also had significantly lower water conductivity than other ponds and a higher proportion of (non-woodland) semi-natural land in its surroundings. Given that ponds are known to contribute significantly to UK biodiversity at a landscape level, and that several thousand new ponds are created each year in the UK alone, the findings suggest that well designed and located pond complexes could be used to significantly enhance freshwater biodiversity within catchments.

Rediscovery of Pelobates fuscus insubricus in the Asti Province, north-western Italy

The amphibians of the pond complex “Stagni di Belangero” in the Po Plain, Asti Province, have been studied. The species living in the pond are Bufo bufo, Bufo viridis, Hyla intermedia, Pelobates fuscus, Rana dalmatina, Rana synklepton esculenta, Rana cf. kurtmuelleri, Triturus carnifex and Triturus vulgaris. Species composition, migration period of P. fuscus, and biometric data are provided. Relevant importance has been given to P. fuscus, since we reconfirm its presence in one of the ponds 13 years after its first finding in the area. This toad is also one of the most threatened species of amphibians in Europe and needs particular attention in order to be protected adequately.

Dynamics of evapotranspiration from a riparian pond complex in the Western Boreal Forest, Alberta, Canada

AbstractThe relative contributions to total actual evapotranspiration (AET) from pond and riparian areas in a pond‐wetland complex in the Western Boreal Plain (WBP) of northern Alberta are measured using the Bowen ratio energy balance technique. Measurements show that a pond typical of the WBP evaporates at a rate more than twice that of the adjacent riparian peatland. Relating the actual to potential evapotranspiration over both surfaces yields Priestley–Taylor α coefficients of 0·69 and 1·11 for the peatland and pond respectively. Further results demonstrate that the sheltering and turbulent influences of the adjacent forested areas must be considered in the processes governing the permanence of WBP ponds. That is, forestry practices may inadvertently enhance the evaporative losses from the ponds, over and above the controls exerted by the regional climate. Copyright © 2006 John Wiley & Sons, Ltd.

Lower to Middle Ordovician evolution of peri-Laurentian arc and backarc complexes in Iapetus: Constraints from the Annieopsquotch accretionary tract, central Newfoundland

The Annieopsquotch accretionary tract in Newfoundland is composed of a series of west-dipping structural panels, each containing remnants of ophiolitic and arc-backarc complexes of Laurentian affinity formed during the Ordovician closure of Iapetus. Panels were transferred from an upper-plate to a lower-plate setting during their Middle to Late Ordovician accretion to the Laurentian margin and become progressively younger eastward. Geochronological data indicate a complex and rapid history of generation and accretion of peri-Laurentian suprasubduction zone rocks. The rapid changes in tectonic environments and the complexity of the relationships are analogous to the complex arc-backarc relationships observed in the western Pacific today. The recognition of the peri-Laurentian provenance of these units based on stratigraphy, geochronology, isotopes, and geochemistry defines the position of the Red Indian Line, the fundamental suture zone in the northern Appalachians, but more importantly enables the development of a realistic tectonic model for the Annieopsquotch accretionary tract involving both thrust and sinistral transcurrent displacements. The oldest and most inboard unit in the Annieopsquotch accretionary tract is the Annieopsquotch ophiolite belt (ca. 480 Ma), which marks the initiation of subduction outboard of the Laurentian margin. The Lloyds River ophiolite complex (ca. 473 Ma) preserves a fragment of younger, more mid-ocean-ridge–like backarc-oceanic crust than the adjacent, structurally overlying Annieopsquotch ophiolite belt. The Lloyds River ophiolite complex originated as a backarc to the Buchans Group (ca. 473 Ma) ensialic bimodal calc-alkaline arc. The panels containing the Annieopsquotch ophiolite belt and Lloyds River ophiolite complex were stitched and overlain by ensialic arc rocks of the Otter Pond Complex (ca. 468 Ma) immediately after their accretion to composite Laurentia together with the structurally underlying Buchans Group. The youngest, structurally lowest two panels comprise the elements of the Red Indian Lake group (465–460 Ma), which record the opening of a backarc basin and the subsequent establishment of a bimodal ensialic calc-alkaline arc sequence. The observed relationships indicate that the Annieopsquotch accretionary tract was generated above a single west-dipping subduction zone outboard of the Laurentian margin over ∼20 m.y. Accretion mainly took place in two stages at ca. 468 and 450 Ma, which correspond with the collision between Laurentia and the Dashwoods ribbon continent and the collision with the peri-Gondwanan Victoria Arc along the Red Indian Line, respectively. Both collisions form part of the Taconic orogeny. The latter, Late Ordovician collision terminated the relatively rapid closure of the main Iapetan tract. The proposed model is similar to the correlative tracts in the British and Irish Caledonides, and may encourage a new look at the New England Appalachians.

Connectivity in an Agricultural Landscape as Reflected by Interpond Movements of a Freshwater Turtle

Connectivity is a measure of how landscape features facilitate movement and thus is an important factor in species persistence in a fragmented landscape. The scarcity of empirical studies that directly quantify species movement and determine subsequent effects on population density have, however, limited the utility of connectivity measures in conservation planning. We undertook a 4-year study to calculate connectivity based on observed movement rates and movement probabilities for five age-sex classes of painted turtles (Chrysemys picta) inhabiting a pond complex in an agricultural landscape in northern Virginia (U.S.A.). We determined which variables influenced connectivity and the relationship between connectivity and subpopulation density. Interpatch distance and quality of habitat patches influenced connectivity but characteristics of the intervening matrix did not. Adult female turtles were more influenced by the habitat quality of recipient ponds than other age-sex classes. The importance of connectivity on spatial population dynamics was most apparent during a drought. Population density and connectivity were low for one pond in a wet year but dramatically increased as other ponds dried. Connectivity is an important component of species persistence in a heterogeneous landscape and is strongly dependent on the movement behavior of the species. Connectivity may reflect active selection or avoidance of particular habitat patches. The influence of habitat quality on connectivity has often been ignored, but our findings highlight its importance. Conservation planners seeking to incorporate connectivity measures into reserve design should not ignore behavior in favor of purely structural estimates of connectivity.

Vegetation patterns and biodiversity of peatland plant communities surrounding mid-boreal wetland ponds in Alberta, Canada

Peatland plant communities surrounding small (<200 ha) boreal ponds were characterized by indicator species, water and peat chemistry, and diversity. Peatland–pond complexes are common in boreal Alberta and are found in three different landforms (clay-till plain, outwash plain, and moraine). Pond area and perimeter were larger in the clay-till plain than in other landforms, although not significantly different. Across the three landforms, cluster analysis detected five peatland communities: marshes, wet open fens, dry open fens, treed fens, and bogs. The zonation pattern of communities surrounding the ponds varied at all sites, and there was no typical pattern, except that marshes were always found closest to water. Based on the bryophyte species, most communities are considered moderate-rich fens. Nonmetric multidimensional scaling indicated communities fell along a wet-to-dry gradient and a bare-to-vegetated gradient. Water depth and temperature, peat depth, and peat C/N ratios differed between open and treed peatland communities, and pH was similar in all communities. Alpha and gamma diversity was highest in the treed fen and lowest in the marsh community in both total species and bryophyte species. The total number of plant species, some of which are considered rare, found in all communities was 139.Key words: marsh, fen, bog, classification, vegetation ecology, diversity.

Inter-clonal variation in phototactic behaviour and key life-history traits in a metapopulation of the cyclical parthenogen Daphnia ambigua: the effect of fish kairomones

We quantified genetic variation for ecological relevant traits in the presence and the absence of fish chemicals of eleven Daphnia ambigua clones that were isolated from six interconnected ponds that differed in water transparency. In a cohort life table experiment, we tested whether genetic variation for a set of key life history traits was present among these clones. In addition the phototactic behaviour of these clones cultured in the presence and the absence of fish kairomones was quantified using a biotest. We detected a significant effect of fish kairomones on the phototactic behaviour and a highly significant genetic variation among clones for this trait in D. ambigua clones isolated from ponds in De Maten. Differences in size at maturity among D. ambigua clones in De Maten were highly significant, whereas differences in spina length among D. ambigua clones in De Maten were not significant. The presence of fish chemicals did not affect the studied life-history traits. We observed a significant positive relationship between average phototactic behaviour for each population and size at maturity both in the presence as in the absence of fish kairomones. Most of the genetic differences could be attributed to a clone isolated from one clearwater pond that is not directly connected to the remainder of the pond complex.

A chemically mediated trade-off between predation risk and mate search in newts

Previous studies have demonstrated that adult male red-spotted newts, Notophthalmus viridescens, are attracted to female sexual pheromones and avoid conspecific alarm substances that signal predation. In this study, we tested the response of red-spotted newts to different concentrations and combinations of macerated male newt extract (MNE) and gravid female odour in the laboratory and field. In the laboratory, males decreased their activity in response to MNE and showed an intermediate attraction (a trade-off) to female odour when paired with MNE. The intermediate attraction indicates that predators may inhibit mate search, and that male newts apparently take greater risks during the breeding season. Results from tests conducted at two sites within the same pond complex demonstrated plasticity in response to MNE. One site showed the laboratory trade-off between mate search and predator avoidance for males, while at the second site, no significant avoidance of MNE was detected for either sex. To explain the discrepancy in MNE avoidance between the sites we propose a trade-off that incorporates risk and resource sensitivity.

Geographical and genetic distances among zooplankton populations in a set of interconnected ponds: a plea for using GIS modelling of the effective geographical distance.

In systems of interconnected ponds or lakes, the dispersal of zooplankton may be mediated by the active population component, with rivulets and overflows functioning as dispersal pathways. Using a landscape-based approach, we modelled the effective geographical distance among a set of interconnected ponds (De Maten, Genk, Belgium) in a Geographic Information System (GIS) environment. The first model (the Landscape Model; LM) corrects for the presence of direct connections among ponds and was based on the existing landscape structure (i.e. network of connecting elements among ponds, travelling distance and direction of the current). A second model (the Flow Rate Model; FRM) also incorporated field data on flow rates in the connecting elements as the driving force for the passive dispersal of the active zooplankton population component. Finally, the third model (the Dispersal Rate Model; DRM) incorporated field data on zooplankton dispersal rates. An analysis of the pattern of genetic differentiation among Daphnia ambigua populations inhabiting 10 ponds in the pond complex reveals that the effective geographical distance as modelled by the flow rate and the dispersal rate model provide a better approximation of the true rates of genetic exchange among populations than mere Euclidean geographical distances or the landscape model that takes into account solely the presence of physical connections.

Wading Bird Depredations on Channel Catfish Ictalurus punctatus in Northwest Mississippi

Abstract.We interviewed farm managers about their perceptions of wading bird problems and conducted preliminary surveys of wading bird populations at 67 randomly selected channel catfish Ictalurus punctatus pond complexes in northwest Mississippi during December 1995. At a subsample of 24 complexes and 10 other complexes previously surveyed in 1990, we surveyed wading bird populations bimonthly throughout the year in 1996 and observed great blue herons Ardea herodias and great egrets Ardea alba feeding at catfish ponds. Seventy‐five percent of farm managers questioned felt that wading birds were causing losses to their fish stocks, and 74% believed the problem was increasing. Consistent with interview results, 88% of the pond complexes surveyed had one or more wading birds present. Despite reported harassment programs by producers, great blue heron densities at 10 complexes previously surveyed in 1990 had increased by more than eightfold in 1996. Great blue heron densities varied with location, season and time of day, but the average 127‐ha farm supported about 78 herons and 56 great egrets. Despite similar populations, the potential impact of these two species was quite different. Live catfish, averaging 10.3 cm in length (circa 10 g) comprised only 8% of the egret diet by weight, and most of the fish were obtained from fingerling ponds during periods when these fingerlings may be weakened by the bacterial disease, enteric septicemia of catfish. In contrast, live catfish, averaging 16 cm in length (circa 34 g), comprised 44% of the great blue heron diet by weight. Herons foraged from both fingerling and food fish ponds, primarily in the early morning and evening. Based on average population densities and foraging rates, herons at the average 127‐ha farm in northwest Mississippi consumed 114,000 (circa 3,900 kg) catfish, annually. However, further studies are recommended to document production losses.

Ammonia removal in a pilot-scale WSP complex in Northeast Brazil

Ammonia removal was monitored in a waste stabilisation pond complex comprising ponds of different geometries and depths under two different operational regimes. It was found that a high degree of ammonia removal commenced in the secondary maturation ponds, with the highest removals occurring in the shallowest ponds as a consequence of improved aerobic conditions. The tertiary maturation ponds produced effluents with mean ammonia concentrations of < 5 mg N/l, the maximum permitted recommended by Brazilian environmental legislation for the discharge of effluents of wastewater treatment plants into surface waters. Ammonia removal in the secondary facultative and maturation ponds could be modelled using equations based on the volatilization mechanism proposed by Middlebrooks et al. (1982).

The performance of an innovative tropical experimental waste stabilisation pond system operating at high organic loadings

In this study on the experimental pond complex at the Federal University of Paraiba in NE Brazil the organic loadings were were more than doubled to investigate the effect on pond performance. The results emphasise the tolerance of the pond system at high loadings without odour production or significant loss of efficiency in terms of BOD removal and bacterial pathogen removal, although nutrient removal by the maturation ponds was reduced. At high organic loadings baffled maturation ponds were more efficient at faecal coliform removal (FC). A minimum of 3 ponds in series are required to ensure maximum BOD removal. Shallow maturation ponds were also more efficient at FC removal although the depth of the facultative ponds had limited effect on BOD removal efficiency.

Ammonia removal in a pilot-scale wsp complex in northeast Brazil

Ammonia removal was monitored in a waste stabilisation pond complex comprising ponds of different geometries and depths under two different operational regimes. It was found that a high degree of ammonia removal commenced in the secondary maturation ponds, with the highest removals occurring in the shallowest ponds as a consequence of improved aerobic conditions. The tertiary maturation ponds produced effluents with mean ammonia concentrations of < 5 mg N/l, the maximum permitted recommended by Brazilian environmental legislation for the discharge of effluents of wastewater treatment plants into surface waters. Ammonia removal in the secondary facultative and maturation ponds could be modelled using equations based on the volatilization mechanism proposed by Middlebrooks et al. (1982).

The performance of an innovative tropical experimental waste stabilisation pond system operating at high organic loadings

In this study on the experimental pond complex at the Federal University of Paraiba in NE Brazil the organic loadings were were more than doubled to investigate the effect on pond performance. The results emphasise the tolerance of the pond system at high loadings without odour production or significant loss of efficiency in terms of BOD removal and bacterial pathogen removal, although nutrient removal by the maturation ponds was reduced. At high organic loadings baffled maturation ponds were more efficient at faecal coliform removal (FC). A minimum of 3 ponds in series are required to ensure maximum BOD removal. Shallow maturation ponds were also more efficient at FC removal although the depth of the facultative ponds had limited effect on BOD removal efficiency.

The Pipestone Pond Complex, central Newfoundland: complex magmatism in an eastern Dunnage Zone ophiolite

Ophiolitic rocks are preserved in both the Notre Dame and Exploits subzones in the Dunnage Zone of the Newfoundland Appalachians. Ophiolites in the Exploits Subzone are generally less well preserved and exposed than their Notre Dame Subzone counterparts and, consequently, have received less attention in the literature.The Pipestone Pond Complex is an Exploits Subzone ophiolitic sequence, which outcrops on the western side of a structural window through the Exploits Subzone into the underlying Gander Zone. It includes a basal harzburgite, which passes upwards into a cumulate pyroxenite and gabbro sequence, and thence into isotropic gabbro intruded by pegmatitic gabbro, diabase, and plagiogranite. There is no sheeted dyke unit. Pillow lava occurs at the top of the sequence but is not observed to be in stratigraphic contact with the intrusive rocks. The ophiolitic rocks are structurally disrupted and no single cross section traverses the complete ophiolitic stratigraphy.Although the stratigraphic sequence of the Pipestone Pond Complex is relatively straightforward, whole-rock geochemical and Nd/Sm isotopic data provide evidence for a complex magmatic history. The intrusive rocks have εNd(t) ranging from −1.1 to + 4 and geochemical signatures indicating derivation from depleted and refractory mantle sources that were clearly influenced by subduction. Within the intrusive rocks, there are no simple petrogenetic relationships among the gabbros and dykes and trondhjemites. The extrusive rocks, in contrast, have εNd(t) of + 7.3 and geochemical signatures similar to those of normal mid-ocean-ridge basalts. They represent magmatism derived from depleted oceanic mantle, not affected by the subducted slab.The tectonic interpretation of the Pipestone Pond Complex is hampered by a lack of definitive evidence for the relative age of the arc-related plutonic rocks and the non-arc-related extrusive rocks. Two possible interpretations are (i) the initiation of subduction under oceanic crust and (ii) arc rifting. The Pipestone Pond Complex is geologically and geochemically analogous to the Boil Mountain Complex in Maine, and together they may form part of an extensive ophiolitic terrane that was emplaced upon the Gondwanan continental margin prior to its collision with Laurentia.

A new Lower Ordovician (Arenig) faunule from the Coy Pond Complex, central Newfoundland, and a refined understanding of the closure of the Iapetus Ocean

A newly discovered fossiliferous horizon within sediments belonging to the Coy Pond Complex of the Exploits Subzone in central Newfoundland yields the graptolite Undulograptus austrodentatus s.l. and cyclopygid trilobite Cyclopyge grandis brevirhachis. This late Arenig faunule constrains the upper age limit of the ophiolite complex and is the first record of an Early Ordovician cyclopygid trilobite in North America. This is consistent with a paleogeographic affinity for south-central Newfoundland with the northern oceanic margin of Avalonia in a peri-Gondwanan position during the Early Ordovician and contrasts with coeval shelly and graptolitic faunas from the Notre Dame Subzone of central Newfoundland, which show marked Laurentian affinities. The Exploits Subzone is generally considered equivalent to the region of Scotland lying south of the Southern Upland Fault. The Newfoundland discovery, which is supported by faunal data from elsewhere in Newfoundland and in Ireland, suggests that the region around the Southern Upland Fault, rather than the Solway Firth, represents the location of the "Iapetus suture" in Britain in Lower Ordovician rocks.

The effect of beaver ponds on the nonpoint source water quality of a stream in Southwestern Wyoming

Currant Creek, a second order stream in southwestern Wyoming, has three large complexes of beaver ponds midway along its 32 km length. To determine whether these ponds improve the quality of water flowing through them, during spring and summer of 1984 and 1985 water samples were taken upstream from, within, and downstream from the pond complexes. During periods of high flow (i.e. spring runoff), concentrations of suspended solids (SS), total phosphorus (TP), sodium hydroxide-extractable phosphorus (NaOH-P, an index of biologically available P) and total Kjeldahl nitrogen (TKN) were reduced in water flowing through the beaver ponds. During low flow, beaver ponds had less effect on these parameters. Concentrations of nitrate nitrogen (NO 3-N) were reduced during both high and low flows, while concentrations of ortho-phosphate ( ortho-P) did not appear to be affected by beaver ponds. Ammonia nitrogen almost always was at the limit of detection. Regression of NaOH-P versus [SS plus ortho-P] suggested that the primary source of NaOH-P was SS. In general, SS explained a large portion of the variation in TP, TKN, and NaOH-P, and often ortho-P was significantly correlated to TP. The increase in the concentration of most parameters below the area with dam complexes appears to reflect input from bank and channel erosion, and export of SS, TP, TKN and NO 3-N from beaver dam complexes was calculated to be less than that from stream sections above or below the dams. Thus the location of dams should be considered before using them to try and improve water quality. The apparent importance of bank and channel erosion as the primary source of nutrients to Currant Creek contrasts with many watersheds in agricultural areas.

Geochronology of ophiolites of the Newfoundland Appalachians

Precise U/Pb zircon ages (2σ errors) are reported for four ophiolite complexes from the Newfoundland Appalachians.Zircons from trondhjemite from Blow Me Down Mountain, Bay of Islands Complex, give an age of [Formula: see text] (five points). Those from gabbro from Blow Me Down Brook give a minimum 207Pb/206Pb age of 480 Ma (one point), confirming that this is the age of the main plutonic episode. These data refute previously determined latest Cambrian U/Pb zircon and Sm/Nd (mineral–rock isochron) ages of 504 ± 10 and 505 Ma for the complex.Gabbro from the Betts Cove Complex yielded zircon that gives an age of [Formula: see text] (four points). This refutes the interpretation of an earlier U/Pb (zircon) age of 463 ± 6 Ma for a trondhjemite dyke as the age of the ophiolite. It was inconsistent with the presence of Arenigian graptolites in the overlying Snooks Arm Group.Two zircon ages from a pegmatitic and medium-grained trondhjemite of the Annieopsquotch Complex are [Formula: see text] (five points) and [Formula: see text] (two points). Zircon from trondhjemite of the Pipestone Pond Complex of central Newfoundland gives an age of [Formula: see text] (five points). Analysis of a single zircon fraction from the Coy Pond Complex gives a minimum 207pb/206pb age of 489 MaThe ages are comparable to those of the Lushes Bight Terrane, Newfoundland, the M'Clintock West Massif, Arctic Canada, and the Ballantrae Complex, Scotland, and together span 18 Ma of the Tremadocian and Arenigian stages. This short age range may imply that only young "hot" oceanic crust was emplaced and preserved in the Appalachian–Caledonian mountain belt.

A tectonic window in central Newfoundland? Geological evidence that the Appalachian Dunnage Zone may be allochthonous

In the Through Hill area of central Newfoundland, mafic to ultramafic complexes, which preserve varying amounts of ophiolite stratigraphy, mark the trace of a major fault zone that outcrops in a roughly elliptical pattern. The major, northeast-trending axis is about 60 km and the shorter axis is about 30 km in length. The most complete ophiolite stratigraphy is preserved in the Coy Pond and Pipestone Pond complexes, which have steep dips and face east and west, respectively, outwards from the centre of the ellipse.The ophiolitic rocks are bounded on the outside by rocks typical of the Dunnage Zone of central Newfoundland, principally Lower to Middle Ordovician volcanic and volcaniclastic rocks interpreted to be of island-arc affinity (Davidsville, Victoria Lake, and Baie d'Espoir groups, Cold Spring Pond Formation) and Upper Ordovician to Silurian clastic sediments (Botwood Group). The volcano-sedimentary sequences are interpreted to have been deposited on the ophiolite conformably, but the contacts are not exposed. Both ophiolite and volcano-sedimentary sequences have similar structural and metamorphic histories, exhibiting one principal deformation and the formation of folds with subhorizontal axes, local development of second-generation folds and associated cleavage, and an intervening period of metamorphism in the greenschist facies.The elliptical area enclosed by the ophiolite belt is referred to as the Mount Cormack Terrane, and is underlain by variably metamorphosed shale, quartz-rich sandstone, quartzo-feldspathic to amphibolitic gneisses, and granite. A limestone occurrence contains shelly fossils of Early to Middle Ordovician age. An early deformation formed folds with steep axes, and subsequent metamorphism resulted in a progression from greenschist facies to upper amphibolite facies, with the production of migmatite and granodiorite.The preferred interpretation of the geology is that the elliptical Mount Cormack Terrane is exposed as a window through an overlying allochthon composed of ophiolitic and volcano-sedimentary rocks of the Dunnage Zone. The emplacement of the allochthon probably postdated deposition of the Silurian Botwood Group. Paleontologic, lithologic, and structural considerations suggest that the sediments of the Mount Cormack Terrane were deposited at the eastern margin of Iapetus and are perhaps correlatives of rocks exposed in the Gander Zone. This implies that the Dunnage Zone has been thrust, probably in an eastwards direction, on a scale comparable with the allochthons mapped in the Scandinavian Caledonides and proposed for the Appalachians of Quebec and the United States.