Isle Of Mull Research Articles

The production of a glass toggle

A glass toggle was found among the ashes of a domestic hearth during the excavation of an unenclosed Iron Age settlement at Kilninian, Isle of Mull, Argyll, Scotland. The hearth was radiocarbon dated to 168 cal bc–cal ad 3 (SUERC-46765). The toggle was covered with a black residue that was stuck to its surface and it looked hastily made, using low-quality aqua cullet. Chemical analyses, using LA-ICP-MS, indicate the glass used was a natron-based glass. The trace element composition suggested the glass was produced in the east Mediterranean area using coastal sands and had subsequently been recycled. The morphological examination using extended depth of field microscopy and micro-computed tomography revealed the toggle was shaped at low temperatures using contaminated glass. The black sooty residue found on the surface of the toggle was found to extend within the toggle and was fused with the object. This could only have happened during manufacture, when the glass was still hot enough to be malleable and stick to the contamination. The uncleaned residues on the surface and the presence of the unpolished pontil scar suggest the toggle may have fallen in the hearth during manufacture and was lost to its maker. Analyses of other glass toggles found in Scotland and Ireland confirmed that natron-based glass had also been used and the toggles were made in the same way as that from Kilninian.
 Canmore ID 148437

Chapter 7 Scottish mineral Geological Conservation Review sites – Metamorphic minerals

Much of Scotland north of the Highland Boundary Fault has been affected by regional and, to a lesser extent, thermal metamorphism and minor metasomatism which, through variable temperatures and pressures, has produced a range of metamorphic minerals. This paper, the seventh of eight on Scottish Mineral Geological Conservation Review Sites, describes ten sites of the highest conservation value within the Lewisian, Moine and Dalradian terranes of the Scottish Highlands, together with thermally altered inclusions in Paleogene volcanic rocks. The minerals featured include the constituents of pelitic and semipelitic schist, such as kyanite and staurolite, unusually large garnet with orthopyroxene and clinopyroxene in ultramafic rocks, and calc silicate minerals, such as tremolite, actinolite, diopside and epidote, together with phlogopitic mica. One site is noted as having stratabound pyrite, chalcopyrite and sphalerite along with large concentrations of chromium mica. The presence of kyanite and tourmaline on the Ross of Mull is one of the few significant mineral sites within rocks of the Neoproterozoic-age Moine Supergroup.Six of the sites encompass extremely rare minerals, generated by the metamorphism of precursors with unusual rock compositions. Foremost amongst these are the barium minerals celsian, cymrite and hyalophane, and the first recorded occurrence in Great Britain of armenite. Although a range of amphibole species occur in both meta-igneous and metasedimentary rocks of the Scottish Highlands, the iron-magnesium clinoamphiboles of the grunerite-cummingtonite series are extremely rare. Indeed the site described in this paper is one of only two occurrences of cummingtonite within the Precambrian-age Dalradian Supergroup. In some cases, the regional mineral assemblages, including the cummingtonite-bearing rocks, have been overprinted by subsequent high temperature/low pressure thermal events associated with the emplacement of igneous intrusions. Pre-eminent amongst the thermal sites must be the occurrence of mullite and sapphire in aluminous shale xenoliths entrained within Paleogene-age basaltic lava flows on the Isle of Mull.

Petrogenesis of the Loch B\xe0 ring-dyke and Centre 3 granites, Isle of Mull, Scotland

The Loch Bà ring-dyke and the associated Centre 3 granites represent the main events of the final phase of activity at the Palaeogene Mull igneous complex. The Loch Bà ring-dyke is one of the best exposed ring-intrusions in the world and records intense interaction between rhyolitic and basaltic magma. To reconstruct the evolutionary history of the Centre 3 magmas, we present new major- and trace-element, and new Sr isotope data as well as the first Nd and Pb isotope data for the felsic and mafic components of the Loch Bà intrusion and associated Centre 3 granites. We also report new Sr, Nd and Pb isotope data for the various crustal compositions from the region, including Moine and Dalradian metasedimentary rocks, Lewisian gneiss, and Iona Group metasediments. Isotope data for the Loch Bà rhyolite (87Sr/86Sri = 0.716) imply a considerable contribution of local Moine-type metasedimentary crust (87Sr/86Sr = 0.717–0.736), whereas Loch Bà mafic inclusions (87Sr/86Sri = 0.704–0.707) are closer to established mantle values, implying that felsic melts of dominantly crustal origin mixed with newly arriving basalt. The Centre 3 microgranites (87Sr/86Sri = 0.709–0.716), are less intensely affected by crustal assimilation relative to the Loch Bá rhyolite. Pb-isotope data confirm incorporation of Moine metasediments within the Centre 3 granites. Remarkably, the combined Sr–Nd–Pb data indicate that Centre 3 magmas record no detectable interaction with underlying deep Lewisian gneiss basement, in contrast to Centre 1 and 2 lithologies. This implies that Centre 3 magmas ascended through previously depleted or insulated feeding channels into upper-crustal reservoirs where they resided within and interacted with fertile Moine-type upper crust prior to eruption or final emplacement.

The Interpretation of Mesolithic Structures in Britain: New Evidence from Criet Dubh, Isle of Mull, & Alternative Approaches to Chronological Analysis for Inferring Occupation Tempos & Settlement Patterns

The number of Mesolithic structures known in Britain has significantly increased since 2000, providing new opportunities for economic and social interpretations of this period. We describe a further structure, represented by features from the Mesolithic site of Criet Dubh, Isle of Mull. We compare the inferred Criet Dubh structure to other Mesolithic structures from Britain, notably those described as ‘pit-houses’. We then consider the implications of the radiocarbon dates from such structures for the tempo of occupation and past settlement patterns. While the use of Bayesian analysis of radiocarbon dates has encouraged interpretations of prolonged occupation and sedentism, we propose alternative interpretations with patterns of intermittent occupation for Criet Dubh and the pit-houses, involving their re-use after extended periods of abandonment within a sparsely populated landscape. The ability to debate such interpretations reflects the transformation in Mesolithic research made possible by the discovery of such structures, the use of multiple radiocarbon determinations, the application of Bayesian analysis, and the exploration of associations between cultural and environmental change. These developments have made the Mesolithic a particularly innovative period of study.

Hen harrier Circus cyaneus nest sites on the Isle of Mull are associated with habitat mosaics and constrained by topography

ABSTRACTCapsule: Hen Harriers Circus cyaneus on the Isle of Mull, UK, are associated with habitat mosaics consisting of moorland, scrub and forestry but avoid grazed land, suggesting that forested habitats could be managed sympathetically for the Hen Harrier in the future should the current UK population increase.Aims: To use distribution modelling to investigate nesting habitat associations using a long-term data set for the Hen Harrier on Mull.Methods: We develop area-interaction models using a least absolute shrinkage and selection operator penalty to explore the distribution of 102 Hen Harrier nest sites in relation to habitat and topography. Our model is then successfully validated in tests using data for 70 nest sites from subsequent years.Results: Our model is effective in predicting suitable areas for Hen Harrier nest sites and indicates that Hen Harriers on Mull are found in habitat mosaics below 200 m above sea level. Hen Harrier nest intensity is positively associated with increasing proportions of moorland and scrub, open canopy forestry and closed canopy forestry. Nest intensity is negatively associated with increasing proportions of grazed land.Conclusion: Hen Harriers avoid grazed areas but are relatively tolerant of other habitat combinations. These findings are supported by previous observations of Hen Harrier habitat use and have implications for the recovery of some Hen Harrier populations in Special Protection Areas and future forest management. Open canopy forest and forest mosaics could potentially be incorporated into landscape-scale conservation plans for Hen Harriers using the population on Mull as an example.

The marine soundscape off the Isle of Mull in Scotland's Inner Hebrides

The waters around the Isle of Mull, Scotland are home to minke whales, basking sharks, common and bottlenose dolphins, harbor porpoises, and many fish and marine invertebrates. This talk describes the soundscape of this region, measured as part of a study on minke whale (Balaenoptera acutorostrata) acoustic habitat use, conducted June–September 2016. The study area consists of shallow (<100 m depth) shelf waters between and around the Islands of Mull, Coll, and Muck. Measurements were made with a Soundtrap 300 from multiple points over the study area (~560 km2) at a sampling rate of 288k Hz. Recordings were taken at a depth of ~30 m from a whale watching vessel when it was stopped (usually observing marine wildlife). The study includes 131 recordings with durations of 5–40 min. Spectral density varies with location and time over the study. Temporal and regional variation and the identity of various sounds are analyzed. Most of the acoustic energy in the region is concentrated below 50 kHz. The soundscape is dominated by wave noise, snapping shrimp, and distant dredging. Local areas or times may be dominated by transient biological sounds, e.g., the calls of common dolphins. Regular but infrequent ferry passage temporarily alters the base soundscape.

Reflective Drawing as a Tool for Reflection in Design Research

AbstractThis article explores the role of drawing as a tool for reflection. It reports on a PhD research project that aims to identify and analyse the value that co‐design processes can bring to participants and their communities. The research is associated with Leapfrog, a three‐year project funded by the UK Arts and Humanities Research Council (AHRC). It aims to transform public engagement through activating participation using co‐design practices. The article reports on the analysis of initial research findings arising from a series of workshops with members of non‐profit organisations on the Isle of Mull, in the Highlands and Islands of Scotland, in which co‐design practices were used. The article reflects on the use of drawing used as a tool to capture the author's reflections and her own personal development as a researcher. In this study the term ‘reflective drawing’ refers to the use of drawing as a tool to support the research reflection process within an ethnographic approach to the fieldwork. Reflective drawing is used in two different stages of the reflection process: (1) to record data during fieldwork enabling reflection‐in‐action, complementing field notes and disclosing visual and kinaesthetic learning; and (2) to recall lived experience during the reflection sessions conducted after the observed activity, which helps to establish a bridge between theory and practice. Reflection is defined as an intuitive process that enables the understanding of oneself within a context of practice. Hence, understanding reflective drawing requires exploration of the reflection process.

Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland

Sill emplacement is typically associated with horizontally mechanically layered host rocks in a near-hydrostatic far-field stress state, where contrasting mechanical properties across the layers promote transitions from dykes, or inclined sheets, to sills. We used detailed field observations from the Loch Scridain Sill Complex (Isle of Mull, UK), and mechanical models to show that layering is not always the dominant control on sill emplacement. The studied sills have consistently shallow dips (1°–25°) and cut vertically bedded and foliated metamorphic basement rocks, and horizontally bedded cover sedimentary rocks and lavas. Horizontal and shallowly-dipping fractures in the host rock were intruded with vertical opening in all cases, whilst steeply-dipping discontinuities within the sequence (i.e. vertical fractures and foliation in the basement, and vertical polygonal joints in the lavas) were not intruded during sill emplacement. Mechanical models of slip tendency, dilation tendency, and fracture susceptibility for local and overall sill geometry data, support a radial horizontal compression during sill emplacement. Our models show that dykes and sills across Mull were emplaced during NW–SE horizontal shortening, related to a far-field tectonic stress state. The dykes generally accommodated phases of NE–SW horizontal tectonic extension, whereas the sills record the superposition of the far-field stress with a near-field stress state, imposed by emplacement of the Mull Central Volcano. We show that through detailed geometric characterisation coupled with mechanical modelling, sills may be used as an indication of fluctuations in the paleostress state.

Testing and validation of the ACCESS system

With the increasing penetration of distributed renewable generation, a number of solutions have been developed to avoid network overloads. Several of the schemes already implemented are based on generation curtailment during times of high generation and low demand. The assisting communities to connect to electric sustainable sources (ACCESS) system implements a more sophisticated predictive solution: the generation resource and electrical demand are predicted and the storage heating load is managed accordingly, providing a demand side management instead of a generation curtailment solution. The ACCESS system was installed, tested and demonstrated in the power networks demonstration centre (PNDC), a research facility that enables realistic testing of novel hardware and network operation schemes in a controlled environment, in 2015. Following the testing at the PNDC, the ACCESS system was deployed on the Isle of Mull in 2016. This study reports on the findings from testing of the demand response features of the ACCESS system at the PNDC prior to its deployment on the Isle of Mull. This study reports on the different components of the system; the test regime undertaken at the PNDC; the results of the testing; and the updates to the ACCESS system based on the test results.

Monks, priests and farmers

A community research excavation centred on Baliscate on the Isle of Mull (NGR: NM 49677 54068) took place in autumn 2012. The excavation has revealed the existence of a thriving 6th-century agricultural settlement which was either adopted or replaced by a 7th-century Christian community which appears to have been a monastic establishment. The continued ecclesiastical nature of the settlement into the 9th and 10th centuries is attested by the presence of a later enclosure/vallum and a rectangular structure interpreted as a leacht. In the late 11th or early 12th century, a stone and turf bow-ended structure was built which probably functioned as a longhouse or hall. This structure was later used in the 12th century to house a large corn-drying kiln. Although no 11th- or 12th-century structures were identified adjacent to the leacht, occupation deposits were identified. Then, in the late 13th or early 14th century, a wattle and turf structure was built over these deposits and the remains of a seventh- to eighth-century cemetery. This structure burnt down and was rapidly replaced by a new stone and turf structure enclosed by a rectangular stone and turf enclosure. This is tentatively interpreted as an enclosed chapel, but the evidence is contradictory and it may have simply been an enclosed farmstead. Occupation around the site continued in one form or another until the 16th century and thereafter the site was used intermittently. The excavation has highlighted how little we know about the so-called enclosed chapel sites of Argyll and the absence of evidence for the early Christian church.

Fossil trees, tree moulds and tree casts in the Palaeocene Mull Lava Field, NW Scotland: context, formation and implications for lava emplacement

ABSTRACTMegafossils and macrofossils of terrestrial plants (trees, leaves, fruiting bodies, etc.) are found in sedimentary and pyroclastic units interbedded with lavas in many ancient lava fields worldwide, attesting to subaerial environments of eruption and the establishment of viable plant communities during periods of volcanic quiescence. Preservation within lava is relatively rare and generally confined to the more robust woody tissues of trees, which are then revealed in the form of charcoal, mineralised tissue or as trace fossil moulds (tree moulds) and casts of igneous rock (tree casts, s.s.).In this contribution, we document several such fossil trees (s.l.), and the lavas with which they are associated, from the Palaeocene Mull Lava Field (MLF) on the Isle of Mull, NW Scotland. We present the first detailed geological account of a unique site within the Mull Plateau Lava Formation (MPLF) at Quinish in the north of the island and provide an appraisal of the famous upright fossil tree – MacCulloch's Tree – remotely located on the Ardmeanach Peninsula on the west coast of the island, and another large upright tree (the Carsaig Tree) near Malcolm's Point in the district of Brolass, SW Mull; both occurring within the earlier Staffa Lava Formation (SLF). The taphonomy of these megafossils, along with palynological and lithofacies assessments of associated strata, allows speculation of likely taxonomic affinity and the duration of hiatuses supporting the establishment of forest/woodland communities. The Ardmeanach and Carsaig specimens, because of their size and preservation as upright (?in situ) casts enveloped by spectacularly columnar-jointed basaltic lava, appear to be unique. The aspect of these trees, the thickness of the enveloping lavas and the arrangement of cooling joints adjacent to the trees, implies rapid emplacement, ponding and slow, static cooling of voluminous and highly fluid basaltic magma. The specimens from Quinish include two prostrate casts and several prostrate moulds that collectively have a preferred orientation, aligning approximately perpendicular to that of the regional Mull Dyke Swarm, the putative fissure source of the lavas, suggesting local palaeo-flow was directed towards the WSW. The Quinish Lava is an excellent example of a classic pāhoehoe (compound-braided) type, preserving some of the best examples of surface and internal features so far noted from the Hebridean Igneous Province (HIP) lava fields.These Mull megafossils are some of the oldest recorded examples, remarkably well preserved, and form a significant feature of the island's geotourism industry.

Gene × environment tests discriminate the new EU2 evolutionary lineage of Phytophthora ramorum and indicate that it is adaptively different

SummaryA new evolutionary lineage of the destructive introduced tree pathogen Phytophthora ramorum, EU2 lineage, was recently discovered attacking larch and other hosts in Northern Ireland and south west Scotland, UK. Sixteen ‘medium × agar concentration × incubation temperature’ stress environments were tested to find a rapid and repeatable method to discriminate the known EU2 lineage from the EU1, NA1 and NA2 lineages in culture, in particular from the EU1 already prevalent across the UK; and to investigate whether EU2 might be adaptively different. At 25°C on both Carrot agar and V8 juice agar, the mean radial growth rates of all four lineages were significantly different, with NA2 &gt; EU2 &gt; EU1 &gt; NA1. At this temperature, EU2 colonies were not only phenotypically distinct from EU1 and all other lineages but on average grew three times as fast as EU1. This indicates that EU2 is adaptively different from EU1. Twelve days growth in the environment ‘V8A/2% agar/25°C gave excellent discrimination of all four lineages in three repeat experiments, including clear discrimination of EU2 from EU1. Each lineage exhibited a distinctive colony pattern. The utility of this test environment was examined further by screening fresh UK isolates of unknown lineage from new larch outbreak sites alongside standard isolates. The lineage assignments predicted were corroborated by gene sequencing and RFLP profiling. These results also revealed that the EU2 lineage was present at several new larch sites in south west Scotland, whereas isolates from geographically adjacent areas such as the Isle of Mull, north west Scotland, the Isle of Man and north west England were all of EU1 lineage.

The Lochbuie Marine Institute, Isle of Mull, Scotland

The Lochbuie Marine Institute on the Isle of Mull (Inner Hebrides), established in 1886, had links with the short-lived National Fish Culture Association of Great Britain and Ireland (inaugurated 1882). Its amalgamation with the Scottish Marine Station at Granton (Edinburgh) was informally suggested in 1887, but it ceased to exist about this time.

Native Sn–Pb droplets in a zeolitic amygdale (Isle of Mull, Inner Hebrides)

Despite the particular scientific interest in the elements with high affinity to S and O 2, but found in zero-valence state in nature, the origin of these native minerals has been little explored and remains obscure. Here we describe unique Sn–Pb droplets found in a closed analcime–calcite amygdale collected from a basaltic unit cropping out at Carsaig Bay (Isle of Mull, Inner Hebrides). The droplets consist of intimate intergrowths of nearly pure Sn 0 and Pb 0 domains in proportion 88:12 and are enveloped in a thin, brownish film of organic composition. The occurrence of the Sn–Pb droplets in a closed amygdale, their relationship with the host analcime + calcite and their Pb isotope composition (which does not match any known anthropogenic Pb source) rule out the possibility of anthropogenic contamination and support the natural origin of the Sn–Pb alloy. The variable isotope (Pb, Sr, Nd) compositions in different members of the host basaltic sequence suggest that a parent basaltic magma was modified by crustal assimilation and post-emplacement alteration processes. Considering all possible explanations, it appears that the most likely source of Pb for the Sn–Pb alloy is a discrete basaltic unit with an isotopic composition comparable to the Antrim basalts (Northern Ireland). The amygdale phases, on the other hand, show isotopic evidence for incorporation of elements from both local basaltic and sedimentary units. The apparent isotopic disequilibrium between Sn–Pb droplets and amygdale phases indicates a complex, multi-stage fluid evolution. The occurrence of Sn–Pb droplets in organic capsules suggests that the droplets and the enveloping organic substances are co-precipitates. This implies that the transportation and deposition of Sn and Pb might have occurred through organometallic compounds. We assume interaction of seawater fluids carrying metals leached from basaltic rocks with hydrocarbons from sedimentary units as a prerequisite for the formation of the organometallic complexes. The zeolites lining the basaltic vesicles might have destabilized the migrating organo-Sn and Pb compounds causing their breakdown and precipitation of Sn–Pb alloy.

Using focal species modelling to evaluate the impact of land use change on forest and other habitat networks in western oceanic landscapes

Summary Habitat networks have an important role in combating the deleterious effects of habitat fragmentation on biodiversity. This paper demonstrates how focal species modelling can be used to help predict the effects of land use change on habitat networks in western oceanic landscapes. The modelling was applied to the Isle of Mull in Western Scotland using three focal species: Pseudocyphellaria norvegica (Gyeln.) P. James, a lichen of native broadleaved woodland; marsh fritillary ( Eurodryas aurinia Rottemburg), a butterfl y of damp grassland and song thrush ( Turdus philomelos CL Brehm), an avian habitat generalist. Signifi cant areas of planted conifer forest on Mull will be converted to open ground habitat and native woodland. These land use changes, together with modest expansion of native woodland, are predicted to have a positive impact on networks for the lichen and marsh fritillary without unduly compromising networks for habitat generalists. There may be scope therefore for a more ambitious strategy for developing native woodland and damp grassland networks, but further testing using focal species with more exacting ecological requirements is desirable. Focal species modelling has value in informing strategies for land use change and the development of habitat networks provided that care is taken to select species with relevant ecological requirements.

Reassembling the Paleogene–Eocene North Atlantic igneous province: New paleomagnetic constraints from the Isle of Mull, Scotland

The paleomagnetic data sets from the British Tertiary Igneous Province (BTIP) have recently been criticized as being unreliable and discordant with data from elsewhere in the North Atlantic Igneous Province (NAIP) [Riisager et al. Earth Planet. Sci. Lett. 201 (2002) 261–276; Riisager et al. Earth Planet. Sci. Lett. 214 (2003) 409–425]. We offer new paleomagnetic data for the extensive lava flow sequence on the Isle of Mull, Scotland, and can confirm the paleomagnetic pole positions emanating from important earlier studies. Our new north paleomagnetic pole position for Eurasia at 59 ± 0.2 Ma has latitude 73.3°N, longitude 166.2°E (dp/dm = 5.2/7.0). A re-evaluation and an inter-comparison of the paleomagnetic database emanating from the NAIP were carried out to test for sub-province consistency. We find a general agreement between the Eurasian part of NAIP (BTIP and Faeroes) and East Greenland data. However a compilation of West Greenland data displays a large and unexplained dispersion. We speculate on if this is related to different sense of block rotation of the Tertiary West Greenland constituents. Combining all data from the NAIP constituents, give a pole position at 75.0°N, 169.9°E ( N = 25, K = 84.3, A 95 = 3.2) in Eurasian reference frame.

The Geologic Fault

sublimity of most northern landscapes can overpower a lover of wildflowers like myself, but not Iona. It is the most colorful island I have ever laid my eyes on, even rivaling the tropics. The sky is usually several shades of dark blue mixed with gray swirling clouds. The sea varies from sapphire to green, and often can show several bands of it at the same time. The sand skirting most of the perimeter of the island, except for the southern side facing Ireland, is a bright white. It is impossible to walk anywhere without encountering the many verdancies of heather. The blossom of this ubiquitous flower is too small to be noticed from a distance, though close up it tinges the path in delicate pinks and purples. Strewn everywhere on the beaches are thousands of stones of various sizes cast in reds and creams and deeper reds. In the sound between Iona and the Isle of Mull, only a fifteen-minute ride by ferry, there is an ancient geological fault line, which is why the rocks are so distinct. It makes sense to me. The difference is

FIRST UNEQUIVOCAL MERMITHID–LINYPHIID (ARANEAE) PARASITE–HOST ASSOCIATION

Abstract The first description of a Mermithidae–Linyphiidae parasite–host association is presented. The nematode is preserved exiting the abdomen of the host, which is a juvenile Tenuiphantes species (Araneae, Linyphiidae), collected from the Isle of Mull, UK. An updated taxonomic list of known mermithid spider hosts is provided. The ecology of known spider hosts with regard to the direct and indirect life cycles of mermithid worms suggests that both occur in spiders.

‘What’s the Story in Balamory?’: The Impacts of a Children’s TV Programme on Small Tourism Enterprises on the Isle of Mull, Scotland

Film- and television-induced tourism effects have been witnessed in a number of locations world-wide, creating a range of positive and negative impacts for host communities and environments. The children’s television programme Balamory, filmed on the Isle of Mull, Scotland, has created a new tourism phenomenon for the island, leading to concern that Mull’s reputation as a green destination for the discerning might be displaced by a less desirable form of tourism. Through a questionnaire survey of tourism businesses on Mull, this paper explores the perceptions of television-induced tourism and the effect of Balamory on business activity during the 2003 season, exploring customer numbers, spending, turnover and profitability, along with attitudes to the new visitors. The research also explores the implications for sustainable tourism development, particularly recognising the limited life-span of film- and television-induced tourism and issues relating to displacement of traditional markets, with an emphasis on sustaining tourism as a means of generating revenue to support a rural island community.

Genetic variation in the widespread lichenicolous fungus Marchandiomyces corallinus

The lichenicolous basidiomycete Marchandiomyces corallinus is widely distributed in North America and Europe, where it commonly is found on a variety of lichens. Theoretically either of these characteristics, a wide geographic range or generalized host ecology, could provide opportunities for genetic differentiation within this species. To determine how genetic variation is partitioned in M. corallinus, 12 fungal isolates were obtained from locations in North America and Europe; at two locations, in Washington County, Maine, and on the Isle of Mull in Scotland, fungi also were isolated from different lichen hosts. Vegetative mycelial compatibility tests were used to determine compatibility groupings from among the isolates; in addition, several PCR amplification products (RAPD, nuITS rDNA) were obtained for each isolate. A number of distinct compatibility groups were recognizable based on geography, not host ecology. In addition compatible isolates always were restricted to either North America or Europe. However RAPD markers indicated that compatible isolates are not always genetically identical. The presence of sequence heterozygosity at specific positions indicated that the isolates are heterokaryotic and a number of distinct haplotypes could be identified based on ITS variation at three separate locations. This type of genetic variation in these fungi suggests that sexual recombination is possible and that genetic differentiation has taken place recently as a result of geographic isolation, not host switching.