Ben Ledi Research Articles

Age of the Grampian event: a Discussion of “New evidence that the Lower Cambrian Leny Limestone at Callander, Perthshire, belongs to the Dalradian Supergroup, and a reassessment of the ‘exotic’ status of the Highland Border Complex”

As a contribution to the current debate on the age of the Grampian Orogeny in the Scottish Dalradian, we comment on the valuable paper by Tanner (1995) that establishes stratigraphical continuity between the ‘Dalradian’ Ben Ledi Formation and the ‘Highland Border’ Keltie Water Formation that contains the Lower Cambrian Leny Limestone (Cowie, Rushton & Stubblefield, 1972, p. 17). Tanner's interpretation of the stratigraphy differs in detail from that of Harris & Fettes (1972). We unreservedly accept Tanner's mapping and the stratigraphical changes that follow from it: there are two units of black slate and limestone; that containing the fossiliferous limestone of Leny Old Quarry is the younger.

The Tay nappe and associated folding in the Ben Ledi–Loch Lomond area

Synopsis Recent mapping in the Ben Ledi—Loch Lomond area has shown the southern closure of the Tay nappe to consist of three major folds, the Aberfoyle anticline, Ben Ledi antiform and Benvane synform. The D 1 age of these folds is clearly demonstrated by cleavage-bedding relationships and younging reversals. The previously unrecognised Benvane synform, the structurally lowest major fold, is responsible for the regional inversion of the flat belt. It is defined both on structural and stratigraphical grounds. The D 2 event is dominantly a product of a deformation event in which simple shear increases in intensity downwards. The limit of significant D 2 deformation cuts the major D 1 fold hinges. D 4 is responsible for the Highland Border downbend, the major monoformal structure which divides the area into a flat belt and a steep belt. The steep belt lies adjacent to the Highland Boundary fault and provides a section through the structurally high levels of the Tay nappe.

The structure of the Dalradian rocks in the SW Highlands of Scotland

The structure of the Dalradian rocks between the Loch Skerrols Thrust and the Highland Boundary Fault in Scotland is related to a regional deformation history of eight fold phases. The first four phases are associated with the formation of early, but not necessarily recumbent, folds such as the Islay Anticline, the Loeb Awe Syncline and the Ardrishaig-Aber-foyle Anticline during the primary deformation. The subsequent phases of deformation are related to the development of secondary structures, such as the Tarbert and Ben Ledi Monoforms, which are superposed on the earlier structures. It is argued that the primary structures formed as a result of lateral compression acting at depth. However, as the Ardrishaig-Aberfoyle Anticline reached a high structural level it collapsed towards the southeast under the influence of gravity to form the anticlinal core to the Tay Nappe. This process was continued during the secondary deformation with the development of the Tarbert and Ben Ledi Monoforrns.

Dalradian-?Arenig relations in parts of the Highland Border, Scotland, and their significance in the chronology of the Caledonian orogeny

Synopsis Comparisons of structures in the Jasper and Green Rocks (J.G.R.) (?Arenig) and Dalradian exposed in the River North Esk, near Edzell, lead to the following correlations which are presented in conjunction with the possibly equivalent events in the Central Highland regional history. N orth E sk Central Highlands Regional History J. and G. Rocks Dalradian Near-isoclinal folds with flow cleavage Near-isoclinal folds with flow cleavageGrowth of biotite porphyroblasts F 1 (Tay Nappe, Aberfoyle anticline) Climax of regional metamorphism Tight folds with axial planar strain-slip cleavage Tight folds with axial planar strain-slip cleavage F 3 (Ben Ledi antiform, [‘downbend’], Cowal antiform) Two sets of corrugations and kink bands Two sets of open folds and crenulations F 4 etc. These correlations are supported by evidence that the ?Arenig in Arran is downward facing.

The composition of some Ben Ledi grits and its bearing on the origin of albite schists in the south-west Highlands

Synopsis The Ben Ledi Grits between the Highland Boundary Fault at Loch Venachar and the Balquhidder district contain a considerable proportion of albite of detrital origin. The proportion of Na 2 O in twenty-one new rock analyses of grit bands, which varies from 1.2 to 4.8 per cent, is sufficient to account for the Na 2 O proportions present in the albite schists of the south-west Highlands. It is suggested that these albite schists developed during metamorphism as the result of local transfer of sodium from grit bands to pelitic bands.

Is the Tay Nappe post-Arenig?

Evaluation of the structural data from the Highland Border is important in the discussion of the age of the Caledonian orogeny in Scotland. There is no published account setting out the detailed structural history of the Highland Border Series and making a comparison of the structures in the Highland Border ‘Arenig’ with those in the adjacent Dalradian. This note gives the results of a study in the N. Esk section which was chosen because it provides the most complete exposures of the Highland Border Series and adjacent Dalradian rocks. The section in the N. Esk was examined in detail, from the mouth of the Mooran Burn [NO. 583735] to the Highland Boundary Fault [NO. 594719]. The rocks exposed (Fig. 1) may be conveniently subdivided in two groups separated by the N. Esk Fault which is exposed in the right bank of the river [NO. 587732]. Upstream from the Fault, Dalradian pelitic rocks are succeeded by grits which have been correlated with the Ben Ledi Grits (Anderson 1942, p. 229). Downstream from the Fault lie two bands of grits and shales with limestone (assigned to the Margie Series = Leny Grit and Leny Limestone, Anderson 1947, p. 490), separated by a group of rocks consisting of greenstones and cherty shales. The greenstones and cherty shales of the N. Esk section, together with other rocks at the Highland Border in Kincardine, Callander and in Glen Sannox, have long been regarded as Arenig in age. As a result of recent re-examination of the ...

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.

The Aberfoyle Anticline, Callander, Perthshire

AbstractThe succession in the Upper Dalradian is described. The author follows Anderson in correlating the Leny and Ben Ledi Grits. Way-up evidence indicates that the Leny Limestone does not occupy a syncline as previously supposed, but is a stratigraphical intercalation in the Leny Grits. It is shown from way-up evidence and structural analysis that the Aberfoyle Anticline closes downwards and is a synform.

Folded Fracture Cleavage in the Southern Highlands: Preliminary Note

In the area between Loch Katrine and Loch Venachar in the southern Scottish Highlands, the Ben Ledi grits occur as part of the Dalradian graywackes. In a northwestern belt the grits show strongly folded fracture cleavage, and in a southeastern belt unfolded fracture cleavage. The implications are discussed, and resemblance to a similar relation of structures in the Moine schists of Morar is noted.

XII.—Xenolithic Minor Intrusions in the Loch Lomond District

I. INTRODUCTION. A FEW years ago Sir J. S. Flett (1929)1 described an interesting vogesite dyke which occurs on the western side of Loch Lomond in a small abandoned quarry about one mile S. of Inverbeg Hotel. The dyke is about 16 ft. thick, trends nearly W.S.W. to E.N.E., and hades towards the south at an angle of 75°. It belongs to the suite of minor intrusions accompanying the Newer Granite and Diorite masses of the Southern Highlands, which were injected at the end of the Caledonian orogeny, and are either of late Silurian or early Devonian age. The special interest of this dyke is found in its numerous inclusions; both cognate (pseudo-cognate according to Flett, see p. 379) and accidental xenoliths are present, as well as many scattered xenocrysts of garnet. The schist xenoliths contain an abundance of pink almandine garnet and also some staurolite, and are notable for their high grade of metamorphism, far higher than that of the semi-pelitic schists of the Ben Ledi group which constitute the immediate country rocks of the dyke. Flett concluded “that garnetiferous and staurolitic schists underlie the Ben Ledi series near the south end of Loch Lomond.” He considered that this conception differed from views expressed by certain previous authors, and that it strongly suggested “that the sequence in this part of the Southern Highlands is an ascending one from south to north.” During the recent widening of the Balmaha-Rowardennan road on the eastern side of Loch Lomond, Dr. Tyrrell found This 250-word extract was created in the absence of an abstract

Contact-Metamorphism in the Comrie Area of the Perthshire Highlands

British petrographic literature is now so enriched by the detailed descriptions of contact-metamorphic aureoles, associated with plutonic intrusions—investigations largely conducted by the officers of the Geological Survey, and partly by independent workers—that it might appear that an investigation of an additional contact-zone would bring to light little but the usual well-known mineral-assemblage of aureoles already investigated: In the case of the aureole surrounding the Carn Chois diorite-complex of Perthshire, moreover, an inspection of the 1-inch Geological Survey map would tend to confirm this view—not only as to the nature of the mineral-assemblages, but also as to their apparently restricted variety. The diorite-complex is shown as intruded almost completely within the Ben Ledi Grit stratigraphical zone, touching only at its southernmost point rocks essentially of argillaceous composition— the Aberfoyle Slate-band. Here, then, are presumably sediments of a restricted range of composition; the hornfelses derived from them may be expected to show the same limit of variation. The examination that I have been able to make of this aureole shows quite clearly, however, that such a restriction in chemical composition is far from being the case. The thermal products show a wide range of composition, and the mineral-assemblages in the inner zone of hornfelses include types which (I believe) have not been previously recorded from British contact-zones, and some that I have not been able to match with any of the thermal products of extra-British contact-aureoles. Moreover, these unusual mineral-assemblages are by no means rare in the aureole itself, but have been

II. Notes on the Geology of Glasgow's Highland Park

The peninsula between Loch Long and Loch Goil, hitherto known as “Argyll's Bowling Green,” should be of special interest to local geologists, inasmuch as, thanks to Mr. Cameron Corbett, it is now Glasgow's bowling green, a name resembling that of a street in Damascus reputed by tradition to be “the street which is called Straight,” but which, according to an American traveller, while not quite so straight as a rainbow, is considerably straighter than a corkscrew. Our new possession is somewhat less than 6 miles in length, and somewhat more than 2 miles in average width; it consists of a mountain ridge 2500 feet high at its northern and 1500 feet at its southern limit; the gradient of its slopes is seldom less than 1 in 2, and not infrequently its flanks are precipitous. The southern portion of the peninsula is composed of that zone of arenaceous schists known as the Ben Ledi grits, which give rise to the peculiarly rugged scenery of the Trossachs region. In the more northern parts the softer micaceous phyllites of the series are also in evidence. The foliation of the grits appears to be in this district more or less coincident with the original sedimentary bedding planes of the rock, and, along the shores of Loch Long, dips at a high angle towards the south-east. When followed up Loch Goil the angle of dip is seen gradually to lessen, until the folding becomes nearly horizontal, undulating gently, and dipping sometimes towards the north-west, thus This 250-word extract was created in the absence of an abstract

XXIX. The “Green Beds” on Sron Aonaich and near Ardlui, Argyllshire

Stratigraphically the “Green Beds” occur in a position near the top of the lower arenaceous zone, and occupy a horizon not far below the Loch Tay limestone. It was not until considerable advances had been made in the mapping of the Highlands that the Officers of the Survey were enabled to recognise the importance of the rocks as a definite and well-marked horizon amongst the schists to the south of the Loch Tay limestone, below which and towards the great central facker or fan structure the “Green Beds” dip in simple outcrops below the Loch Tay limestone. Between the great axial line of folding and the frontier Highlands they are repeated again and again in isoclinally-folded strata as outliers between the folds of the Ben Ledi grits. In Cowal there appear to be two sets. The particular specimens from which those exhibited have been taken are on Sron Aonaich, a shoulder of Ben Lomond, and in the railway cutting on the West Highland line north of Ardlui, the principal interest attached to them being the increasing metamorphism seen in the rocks from the latter locality. The Sron Aonaich “Green Beds” are principally pale yellowish greeny grits, the original clastic structures being quite apparent, as they often enclose large pebbles of quartz and felspar. Examined in a thin slice under the microscope the rock is seen to be composed of epidote, quartz, felspar, chlorite, biotite, and two sets of long needle-shaped crystals, one of which gives straight extinction and has a This 250-word extract was created in the absence of an abstract

2. Note on the Origin of Thunderstorms

This Note does not refer so much to those great thunderstorms which extend over hundreds of miles in each direction, as to those small local storms which are often seen of from two to five or six miles only in diameter.It refers particularly to those which are seen, in summer and autumn, to pass down the Tay valley. They almost invariably come from the westward, and I am told each is almost always accompanied by a storm of similar dimensions passing eastwards down the valley of the Forth. So far as I can ascertain, they seem both to commence almost abruptly somewhere in the district about Ben Ledi and Ben Lomond.

XXV. On Some Sections of Carboniferous Limestone near Busby

These sections are situated about seven miles south of Glasgow, a little to the north-east of the Eaglesham Road Station, on the Busby and East Kilbride Railway, and at a height of from five to six hundred feet above the level of the sea. At this place we are near the south-western edge of the Lanarkshire coalfield, and a good idea may be formed of its transverse extent by ascending any of the hills in the district; as, for instance, that to the east of Thornton farm-house. In the distance to the west we descry the Bowling hills and the range of mountains from Ben Voirlich to Ben Ledi, while on the north the Clyde basin is bounded by the trap hills of Campsie and Kilsyth. A corresponding range of trap hills runs behind us on the south. The strata here dip under all the intermediate strata and reappear near the base of the Campsie hills, as we shall afterwards have occasion to notice. Between these points the strata are overlaid by part of the lower limestones, the middle ironstones, and the upper limestones, as well as by strata corresponding to the millstone grit, and the whole, or nearly the whole, of the upper coal measures. The surface of the ground is of an undulating character, rising gradually towards the south. The sections to be described occur at four quarries, viz.,—Thornton, Thornton Hall, Braehead, and Phillipshill—the first being on the southern, the second on the western, and the third and This 250-word extract was created in the absence of an abstract

III.Account of a Botanical Trip to Ben Ledi, with Pupils, in July1860

III.Account of a Botanical Trip to Ben Ledi, with Pupils, in July1860