Grampian Highlands Research Articles

A re‐investigation of the bathymetry of Loch Earn

Abstract A newly prepared bathymetric chart of Loch Earn in the Grampian highlands of Scotland is presented. The continuously recorded echograms reveal that the loch is composed of several basins arranged in steplike progression shallowing eastwards from a greatest depth of 87.2 m. Seismic reflection profiling reveals over 22 m of sediments lining the floor above tills. It is suggested that the waterbody occupies a depression which survived due to the presence of a detached block of stagnant but thick ice during deglaciation, while areas to the east and west were filled with sediments.

The fluvioglacial landforms of mid-Strathdearn, Inverness-shire

Synopsis Glacier ice from the west overran Mid-Strathdearn and built up to become part of the SW–NE moving ice sheet that enveloped the Grampian Highlands 17–18 000 years ago. As the glacier ice wasted away, two contrasting networks of meltwater rivers evolved. Most of the glacial drainage flowed directly downhill and eventually joined the arterial channel of the fluvioglacial River Findhorn, although this route was not completely open to meltwaters until relatively late in the deglaciation. Other meltwater rivers followed ice-directed routes across the slopes and cut channels into intervening spurs and pre-existing cols. There was a major trans-watershed outflow of meltwaters from Mid-Strathdearn to the SE, and a lesser inflow of meltwaters from the NW.

Comparative petrography of deformed and undeformed migmatites from the Grampian Highlands of Scotland

SummaryFabrics in migmatites from Portsoy in the NE Dalradian are compared with those in paratectonic and pretectonic migmatites from deeper structural levels of the Northern Grampain Caledonides. Paratectonic leucosomes, from Portsoy and Mid-Strathspey, have weak biotite fabrics. They lack the biotite foliation which is strongly developed in pretectonic leucosomes from the Upper Findhorn area. In conjunction with the sequence of deformation, intrusion and metamorphism in Banffshire, the fabric data indicate that migmatization at Portsoy was paratectonic with respect to the local F, folding. Partial melts generated in the aureole of the pre-F3 basic intrusions were, in some rocks, still mobile during F3 and completely crystalline only after the formation of small F3 folds. Granitic leucosomes in Mid-Strathspey were formed within the time-span of a deformation episode. Petrographic measurements show that these leucosomes have approximately minimum-melting compositions in Qz-Ab-An-Or, despite some deformation and retrograde alteration. They are comparable with the Portsoy migmatites in grain size and in complexity of leucosome shapes, and they are tentatively interpreted as products of incipient partial melting without dehydration of biotite.

Postglacial Environmental History of Rannoch Moor, Scotland. I. Three Pollen Diagrams from the Kingshouse Area

Pollen stratigraphic investigations are described from three sites on Rannoch Moor in the western Grampian Highlands of Scotland. The profiles are broadly similar and provide a detailed record of vegetational and environ- mental change in the Rannoch Moor area during the early and mid-Postglacial periods. Radiocarbon dates from the base of one profile suggest that glacier ice of the Loch Lomond Readvance had disappeared completely from Rannoch Moor well before 10000 BP, and that by that time dwarf shrub heaths of Empetrum and Juniperus had become firmly established throughout the region. This heathland vegetation cover was replaced first by birch, then by birch-hazel woodland, and subsequently by forests of pine and birch, and pine and alder. Deteriorating climatic conditions which resulted in accelerated rates of leaching, the growth of acid blanket peat, and a marked increase in areas of waterlogged ground, led to the gradual decline of trees and the progressive evolution of the present-day landscape of blanket peat and heather moor.

Radiocarbon dates and deglaciation of Rannoch Moor, Scotland

THE Loch Lomond Readvance affected large areas of the Scottish Highlands, and while the maximal extent of the readvance glaciers is now fairly well established1,2, it is not yet known how long they took to decay3. Three radiocarbon dates have been obtained from a site on Rannoch Moor in the heart of the south-west Grampian Highlands that provide significant new information on the deglacial chronology of Scotland.

Climatic Inferences from Former Glaciers in the South-East Grampian Highlands, Scotland

Abstract Altitudes, lengths, areas, maximum thicknesses and volumes of 27 glaciers that built up in a small area of the Scottish Highlands during the Loch Lomond (Younger Dryas) stadial are given. The influence of direct radiation on the glaciers is calculated taking into account transmissivity of the atmosphere, glacier aspect and surface gradient, and the albedos of ice and snow. Equilibrium firn lines for the glaciers are determined. The computed regional firn line, incorporating the influence of direct radiation had a gradient of 14.5 m/km. Former precipitation values are based on an equation for average annual mass balances of the glaciers during the stadial that incorporates glacier altitude, regional ablation gradient, direct radiation, the influence of avalanching and blowing of snow, and final glacier volume. Average July and January sea-level temperatures of 6°C and at least — 8°C, respectively, are inferred. Snowfall was principally associated with south-east winds and was similar in total to present day but rather differently distributed. Cloud amounts, at least in summer, were greater than now. A more vigorous atmospheric circulation with many depressions moving along more southerly tracks than now may have been related to the junction of polar water and North Atlantic Drift water in the immediate vicinity of the British Isles.

Climatic Inferences from Former Glaciers in the South-East Grampian Highlands, Scotland

Abstract Altitudes, lengths, areas, maximum thicknesses and volumes of 27 glaciers that built up in a small area of the Scottish Highlands during the Loch Lomond (Younger Dryas) stadial are given. The influence of direct radiation on the glaciers is calculated taking into account transmissivity of the atmosphere, glacier aspect and surface gradient, and the albedos of ice and snow. Equilibrium firn lines for the glaciers are determined. The computed regional firn line, incorporating the influence of direct radiation had a gradient of 14.5 m/km. Former precipitation values are based on an equation for average annual mass balances of the glaciers during the stadial that incorporates glacier altitude, regional ablation gradient, direct radiation, the influence of avalanching and blowing of snow, and final glacier volume. Average July and January sea-level temperatures of 6°C and at least — 8°C, respectively, are inferred. Snowfall was principally associated with south-east winds and was similar in total to present day but rather differently distributed. Cloud amounts, at least in summer, were greater than now. A more vigorous atmospheric circulation with many depressions moving along more southerly tracks than now may have been related to the junction of polar water and North Atlantic Drift water in the immediate vicinity of the British Isles.

Late Glacial and Early Postglacial Environmental History of the Central Grampian Highlands, Scotland

Pollen stratigraphic investigations are described from two sites in the central Grampian Highlands, Scotland. At Loch Etteridge, which is situated beyond the presumed maximal extent of Loch Lomond Readvance ice, the basal deposits are of Late Glacial age, with the pollen spectra indicating a milder Interstadialfollowed by a harsher Stadial phase. The overlyinig sediments are Postglacial in age. Four radiocarbon dates were obtained from the Late Glacial deposits, the basal date being in excess of 13,000 B.P. The second site is located on the Drumochter Pass within the mapped Loch Lomond Readvance limits, and contains only Postglacial sediments. Data from the two sites are used to reconstruct the Late Glacial and Early Postglacial vegetational history of the central Grampian Highlands, and also as an aid in the establishment of a Late Devensian glacial chronology for the area.

A pollen diagram from the Pass of Drumochter, central Grampian Highlands, Scotland

Summary Pollen analytical investigations are described from a site on the Pass of Drumochter in the central Grampian Highlands. Three pollen assemblage zones were identified in the profile which spans the mid- and late-Postglacial periods. The earliest vegetational record is of birch and hazel woodland, which was in turn succeeded by the establishment of pine forest, possibly around 7000 B.P. Declining arboreal pollen percentages and increased values for open-habitat taxa in the upper reaches of the profile reflect the impact of Neolithic man in the area, with the destruction of the forests, and the spread of dwarf shrub heath and heather moor across formerly wooded hillsides.

Analogous Evolution of the Burma Orogen and the Scottish Caledonides

Thick turbidite sequences derived from the Bengal Delta are accumulating on the floor of the Bay of Bengal. Eastward subduction has resulted in successive under-thrusting with tectonic emplacement of the turbidites above the subduction zone to form the Indo-Burman Ranges of western Burma. The ranges are separated from the Eastern Highlands of Burma by the Central Lowlands. In Scotland, the Upper Ordovician and Silurian turbidite sequences of the Southern Uplands are comparable to those of the Indo-Burman Ranges; the Midland Valley and the Grampian Highlands, respectively, are similar to the Central Lowlands and the Eastern Highlands. The development of the Midland Valley and the Southern Uplands can be explained by analogy with the Burma orogen. Both orogens show a similar history of sedimentation, igneous activity, and deformation over a period of 100 m.y., but in Scotland, the equivalent events took place about 400 m.y. earlier than in Burma. There is no known equivalent in Burma of the Early Ordovician Grampian orogeny in Scotland. Our comparison suggests that mineralization similar to that in the Burman volcanic arc should be present in andesite of the Sidlaw anticline.

A Late-Glacial Ice Cap in the Central Grampians, Scotland

Using evidence provided by hummocky moraines, end moraines, till sheets, drift limits, erratics, meltwater channels, outwash deposits, ice-contact fluvioglacial forms and major periglacial forms, an ice cap (with associated outlet glaciers) that developed in the central Grampians in Late-glacial times is reconstructed using a three-dimensional approach. The former ice surface is contoured at 50 m intervals. The ice mass had an area of nearly 3oo km2, a volume of 32 km3 and an average thickness of about 10 m. Former firn lines are determined and inferences made about contemporary temperatures and the distribution of precipitation. THE area investigated lies in the centre of the Grampian Highlands astride the major east-west watershed (for location see inset, Fig. 2). It is bounded in the west by the Pass of Drumochter glacial breach (D. L. Linton, I951) and in the east by the straight, fault-guided Glen Tilt trench. Part of the area is known as Gaick Forest, but for brevity the whole will be referred to as the Gaick area. The main relief feature is a plateau at 700-930 m that is limited almost everywhere by a sharp 200-450 m descent to lower ground (Fig. I). The plateau is especially well developed in the western half of the area, although it is here cut clean across by a major glacial breach 400 m deep (Loch an Duin breach). The bounding slopes of the plateau are broken by numerous valleys that trend perpendicular to its edge and thus collectively form a radial system. Unrelated to this radial pattern, on the northern edge of the area, is the Glen Feshie glacial breach (Linton, 1949), immediately beyond which are the Cairngorms. Apart from Linton's contributions on glacial breaching and a brief account by J. K. Charlesworth (I955), the only published work on the glaciation of the Gaick area is by G. Barrow et al. (1913). These authors concluded that glacier ice that accumulated in the Gaick area was subsequently largely surrounded and partly overwhelmed by an ice sheet centred in the western Grampians. Local ice later became important again in parts of the area as the exotic ice became less powerful. The limits of local ice were not specified and a readvance was not proposed. BASIC FIELD EVIDENCE

Late glacial site in the central Grampian Highlands

THE last British ice sheet probably reached its greatest extent 17,000–18,000 radiocarbon yr ago, when it covered much of the British Isles. We suggest here that this ice mass had disappeared 5,000 yr later. Significant new evidence comes from Loch Etteridge in the heart of the Grampian Highlands of Scotland (Fig. 1).

A gravity survey of a region of the Highland Boundary Fault in Scotland

The results of 1591 gravity measurements made in parts of the Midland Valley and the Grampian Highlands of Scotland, flanking the Highland Boundary Fault-zone between Callander and Cowal are described and density units in the Palaeozoic rocks of the area distinguished on the basis of some 800 laboratory measurements. Steep gravity gradients across the Highland Boundary Fault at Callander and Aberfoyle show that its small hade to the north-west, observed at surface, is maintained to a depth of 2400 ft below sea-level, indicating that the fault behaved as a high-angle reversed fault in mid-Devonian times. West of Loch Lomond, the fault continues in general alignment with its course to the east and is inferred to underlie the Carboniferous cover in the Greenock–Inverkip region. The existence of a deep sedimentary basin bounded to the north-west by three step faults and to the south-east by the Highland Boundary Fault is revealed by a gravity low west of Loch Lomond. The basin is probably partly filled by Lower Old Red Sandstone. The maximum thickness of the Lower Old Red Sandstone sediments in the surveyed area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault. On the flanks of the Highland Boundary Fault, the survey has provided information of regional importance: the slate-belt probably occupies a downfolded synform within the Dalradian rocks; the Ochil Fault can have only a small magnitude in the surveyed area; the maximum thickness of the Lower Old Red Sandstone sediments in the area is between 5000 and 6000 ft and the formation thins south-eastwards in the region of the Ochil Fault.

G. S. Johnstone 1966. The Grampian Highlands. (Third Edition) pp. xi + 103, 21 figs., 11 pls. Geological Survey and Museum, British Regional Geology. H.M.S.O., Edinburgh. Price 8s.

G. S. Johnstone 1966. The Grampian Highlands. (Third Edition) pp. xi + 103, 21 figs., 11 pls. Geological Survey and Museum, <i>British Regional Geology</i>. H.M.S.O., Edinburgh. Price 8<i>s</i>.

The distribution of pressure and temperature during Dalradian metamorphism

The formation of sillimanite in association with the development of gneisses and migmatites in the Grampian Highlands and north-eastern Scotland is interpreted as a later superimposition upon a slightly earlier metamorphic pattern characterized in its higher grades by andalusite and kyanite. This earlier pattern is subdivided by three significant isograds: (i) the andalusite isograd, along which andalusite developed from hydrous mineral assemblages; (ii) a kyanite isograd, along which kyanite developed from hydrous mineral assemblages; and (iii) an andalusite–kyanite isograd, dividing the andalusite and kyanite zones, (i) and (ii) are interpreted as dehydration isograds, virtually isothermal; (iii) represents the polymorphic inversion of kyanite to andalusite, with a P/T slope of approximately 12.8 bars/degC. For some 50km southwards from the coastline along the Moray Firth on the western limb of the post-metamorphic Boyndie syncline, the andalusite and andalusite–kyanite isograds form virtually parallel traces; parallelism of isograds with such disparate P/T slopes suggests that isobars and isotherms in this region were parallel. In central Aberdeenshire the inversion isograd diverges from the andalusite isograd, and appears to run along Deeside to meet the kyanite isograd in the south. This is interpreted as indicating a divergence between isobars and isotherms; an antiformal monocline with approximately ne–sw axes is deduced for the thermal surface. To explain this disposition synmetamorphic monoclinal folding is suggested, in which pressure adjustment was instantaneous as sediments were depressed to deeper levels, but the heat content enabled pre-existing isothermal surfaces to be preserved.

The Villages of the Howe of the Mearns

Abstract At the present time, when rural populations are declining throughout northern Scotland, it is worthwhile looking at the historical background to the problem. The pattern of movement is not a simple one of migration from country to town but rather a multi-stage phenomenon from rural areas to small centres, from small towns to larger towns, and also internal migration on a larger scale within the country as a whole. In some areas also a reciprocal movement is taking place with rural areas being redeveloped as recreational, tourist and dormitory centres. In this paper the primary objective is to trace the evolution of the nucleated settlements in the Howe of the Mearns, a small area of south Kincardineshire lying between the Grampian Highlands and the Garvock Hills, a north-easterly extension of the Sidlaws, and to stress the diversity of stimuli both in time and space which have contributed to the growth and in some cases decline of these settlements. The patterns which appear seem to be representa...

Element Distribution in Two Epidiorite Sills from the Central Grampian Highlands of Scotland

AbstractMagmatic differentiation is demonstrated in two epidiorite sills from the Grampian Highlands of Scotland, and the distribution of major and minor elements compared with data given for other intrusions, and for trace elements in the Whin Sill at High Cup Gill, Westmorland. The latter sill has Sr and Ba enriched towards the top. The element distribution for the epidiorite sills indicates that they are overturned. The data are conclusive for one sill but merely suggestive for the other, since such phenomena as multiple injection may also have affected the element distribution. The structural significance is briefly discussed.

Downward-facing structures of the Highland Border

Summary The structures in the Dalradian rocks near the Highland Border of Scotland consistently face downwards. They are upside-down. In the south-western districts they face downwards to the south-east, between Loch Lomond and Aberfoyle vertically downwards and from Aberfoyle to Stonehaven downwards towards the north-west. The view that the Upper Dalradian Ben Ledi Grits and Leny Grits are equivalent and younger than the Aberfoyle Slates which outcrop between them is tentatively supported. The Aberfoyle anticline implied by this view must face downwards, not upwards as previously claimed. The downward-facing structures are connected with the recumbent folds to the north-west. The Carrick Castle anticline, formerly regarded as the hinge at the front of the Loch Tay inversion, is thought not to exist. That hinge is either located in the Aberfoyle anticline, which would thus mark the southern limit of the Loch Tay inversion, or, if the Aberfoyle anticline does not exist, the hinge lies in the Ben Ledi Grits. On either view the roots of the Highland Border structures lie north of the Loch Tay flat belt. The steep zone of down turned and overturned nappes near the Highland Border represents a powerful monocline associated with the Highland Boundary fault. It connects the Grampian Highlands with the Midland Valley. The nappes possibly continue beneath the Midland Valley.

II.—The Moinian and Dalradian Rocks between Glen Roy and the Monadhliath Mountains, Inverness-shire

SynopsisThe paper provides the first detailed geological description of a portion of the Grampian Highlands between Glen Roy in the west and the Monadhliath Mountains in the east. Moinian metasediments comprising thick granulites (Eilde Flags = Central Highland Psammitic Group) followed by a variable series of pelites and impersistent quartzites (Monadhliath Schists = Transition Group) are succeeded by Dalradian Limestone (Kinlochlaggan or Ballachulish Limestone = Basal Calcareous Group). The Monadhliath Schists are shown to be stratigraphically equivalent to those of Lochaber below the Ballachulish Limestone.Structurally the area consists of north-easterly anticlines and synclines which are generally isoclinal and often overturned. Many formational junctions are clearly stratigraphical, but the point is discussed whether tectonic contacts (slides) may also be present. Most of the metasediments are of garnet grade, but in the east there is a poorly-developed kyanite zone, and a well-developed sillimanite zone. The high-grade zones are related to a major migmatite and pegmatite belt (the Strathspey Complex); another pegmatite belt occurs farther west around Loch Laggan. Post-tectonic granite, quartz-diorite, diorite and appinite intrusions are also present. The district is traversed by several important north-easterly faults which are later than both the metasediments and the intrusions.

VI.— The Kinlochlaggan Syncline, Southern Inverness-shire

1. Introduction. The object of the present paper is to give an account of a geologically almost unknown part of Southern Inverness-shire in the vicinity of Loch Ericht, Loch Laggan and Upper Strathspey (Fig. 1). The district forms part of the Grampian Highlands and like most of that region consists mainly of metamorphosed sediments. The area described lies between the well-known north-easterly fault which has determined the deep hollow of Loch Ericht and a parallel fracture, 7 miles to the north-west, which crosses the east end of Loch Laggan. Laterally the area extends for 20 miles from Aonach Beag, a mountain 13 miles south-west of Dalwhinnie, past Kinlochlaggan to a point 2½ miles north-east of Laggan Bridge. Much of the district is remote and mountainous, although the northern part is readily accessible from the Newtonmore-Spean Bridge road, which passes through Laggan Bridge and follows the north shore of Loch Laggan, and from another road leading from Dalwhinnie to the Spey valley and up the latter towards Garva Bridge and the Corrieyairack Pass. Nearly the whole area lies in Sheet 63 of the one-inch to the mile Geological Map of Scotland, a sheet which has not yet been surveyed. Moreover, in geological literature it has never had more than passing mention. Early references were made by Jameson (1813, vol. II, p. 173), Macculloch (1814, p. 435) and Ami Boué (1820, p. 61). The most important was that by Macculloch who noted the limestone quarried at Kinlochlaggan with its associated hornblende-schist and This 250-word extract was created in the absence of an abstract