Moray Firth Basin Research Articles

3-D palinspastic restoration of normal faults in the Inner Moray Firth: implications for extensional basin development

Balanced cross-section techniques, and the construction of a restored section, permit 2-dimensional palinspastic restorations to be made in both compressional and extensional terraines. In 3 dimensions, an equivalent restoration can be made by assuming conservation of bedding-plane area and considering the volume of a stratigraphic interval rather than its cross-sectional area. Extensional basins displaying upper crustal listric normal faulting are particularly amenable to this approach.Computerised 3-D restorations have been made of the Inner Moray Firth basin, offshore Scotland. This basin is not isostatically compensated, and was produced by 7–8% post-Triassic extension, of which 2.5–3% is post-Jurassic, above a detachment surface at 20–25 km depth, close to the base of the crust. Limited lower crustal thinning (and lithospheric stretching) has affected the eastern part of the basin, but this can account for no more than half of the measured upper crustal extension. Some of this shallow extension is probably coupled by low-angle faults or shear zones into major zones of lithospheric stretching such as the North Sea grabens, where it may help account for discrepancies between estimates of lithospheric thinning and upper crustal extension.

Palaeozoic, Mesozoic and contemporaneous megaspores from the Tertiary of southern England: indicators of sedimentary provenance and ancient vegetation

Megaspores are recorded from several localities in the Thanet and Reading Beds (upper Palaeocene) of southern England. Evidence from their taxonomic affinity, colour, compression and state of preservation indicates three separate groups: two reworked from lower Westphalian Coal Measures and Lower Cretaceous sequences, respectively, and one of contemporaneous forms. Mesozoic megaspores redeposited in the British Tertiary have not previously been recorded. Isolated Carboniferous forms have been found before but their possible value in provenance studies has not been fully explored. The new material includes a diverse assemblage of numerous Westphalian and Lower Cretaceous forms from a single horizon in the Thanet Beds. Of possible source areas it seems most likely that these spores were reworked from the Moray Firth Basin, and elsewhere near the present eastern coast of Scotland, by means of longshore drift following a roughly N–S palaeocoastline. Evidence from other studies of heavy mineral assemblages and palaeogeography also indicates derivation of Thanet Beds sediments by this means. The Cenozoic megaspores include an Azolla (water fern) and two distinct lycopsid forms, one probably of selaginellalean and one of isoetalean affinity. These latter provide the first clear evidence of lycopsids in British Tertiary floras and expand our knowledge of freshwater macrophytes of that time. The assemblages of Minerisporites show morphological trends which may prove to be of biostratigraphic value.

Upper Jurassic stratigraphy and sedimentary facies in the Central Outer Moray Firth Basin, North Sea

The Upper Jurassic of the Outer Moray Firth Basin can be divided into two main stratigraphic units — the Piper and Kimmeridge Clay Formations. In each of these formations five major sedimentary facies can be recognized. The Piper Formation, of late Oxfordian to early Kimmeridgian age, comprises very fine to coarse-grained sandstones and minor mudstone of clastic shelf to shoreline origin. Large scale upward-coarsening sequences are well developed in some areas, particularly in the reservoir sands of the Tartan oilfield, and are interpreted as regressive, possibly deltaic deposits. The unconformably overlying Kimmeridge Clay Formation ranges in age from late Oxfordian through Volgian to Ryazanian. The formation is predominantly argillaceous, but also contains locally thick accumulations of sandstone deposited by gravity flow processes. The Claymore Sandstone Member is proposed as a new name for these sandstones in the region of the Claymore oilfield, where they form the major reservoir. Sands of the Piper Formation were derived mainly from the south-west, although some input from the north may also have occurred. Deposition may have extended further eastwards than the present erosional limit of the sands. Thick sand sequences in the Kimmeridge Clay Formation are probably restricted to the margins of the Witch Ground Graben, where contemporaneous faulting occurred.

The Permian Weissliegend of NW Europe: The partial deformation of aeolian dune sands caused by the Zechstein transgression

The Weissliegend is a European sandstone unit of largely late Early Permian age. It is underlain by the Early Permian Rotliegend red desert sandstones and is overlain by the conventionally accepted basal bed of the Zechstein-the bituminous marine shales of the Kupferschiefer. The Weissliegend sandstones are characteristically white or grey in colour and have been recognised beneath the North Sea, in Germany and in Poland. Equivalents, which are red or yellow in colour, occur in NE England and at the southern edge of the Moray Firth Basin in Scotland. From an examination of cliff and quarry exposures in Britain, and of drill cores from southern North Sea gas wells, it is now believed that the bulk of the Weissliegend sandstones (and their equivalents) were originally deposited as aeolian dunes. These dune sands, however, were later modified by a widespread event, the Zechstein transgression, which caused their partial homogenisation, the creation of large-scale soft-sediment deformation structures, and the local and minor reworking of some of the dune flanks. The preferred mechanism of deformation is interpreted as: (1) entrapment of large pockets of air within the bodies of the dunes by flanking and overlying wetted dune sands; (2) venting of the air pockets when the rising internal air pressures overcame the weight of the hydrostatic head of water and the capillary (cohesive) strength of the overlying wetted sands; (3) the rapid replacement of air by water, which caused liquidisation of the original dune laminae; and (4) the associated collapse and final consolidation of the sands into a tigher packing configuration. Deformations seem to be more developed in former transverse dunes than in seif dunes. The reason may be that the relatively tightly packed low-angle accretion bedding common on the flanks of seif dunes is more resistant to deformation than the looser avalanche sands that form a major part of transverse dunes. Limited reworking of former dune sands was probably best developed on the steep lee slopes of transverse dunes and the steeper upper slopes of seif dunes. The lack of reddening of the Weissliegend sandstones-proper is attributed to a combination of their accumulation above the Rotliegend water table, to the rapidity of the Zechstein transgression, and to the anoxic state of the early Zechstein sea floor. The Weissliegend sands, unlike the underlying Rotliegend into which they grade, were thus never in a diagenetic environment that was conducive to reddening. Finally, it is recommended that the term Weissliegend be dropped in any formational sense. It should only be retained for the Weissliegend proper, and their equivalents, to denote a complex facies association dominated by (1) the uppermost Early Permian Rotliegend dune sands (now partly deformed) that lay above the water table just prior to the Zechstein transgression, together with (2) the minor erosional marine products caused by that transgression. The latter, sensu stricto, are Zechstein sandstones of earliest Late Permian age.

Early Permian (Rotliegendes) palaeowinds of the north sea

The classical desert sediments of the Early Permian Upper Rotliegendes were deposited in a post-Variscan basin that extends from eastern England to the Russo-Polish border, which has been referred to as the Southern Permian Basin. These sediments comprise four main depositional facies: fluvial (wadi), aeolian, sabkha and lacustrine. The lacustrine facies includes important bedded halites. The Southern Permian Basin is separated from the smaller Northern Permian Basin by the fragmented Mid North Sea-Ringkøbing-Fyn system of highs: and beyond the Grampian Spur lies the even smaller Moray Firth Basin. These latter basins contain rock sequences similar to those of the southern basin, with the exception that bedded halite has not been recognised in the lacustrine facies. The Rotliegendes of the southern basin apparently conforms to deposition in a Northern Hemisphere tradewind desert similar to the modern southern Sahara. Apart from regional palaeomagnetic considerations and the occurrence of sediments of a non-arid nature south of the Variscan Highlands, the strongest evidence supporting this interpretation is the pattern of palaeowind directions deduced from the orientations of dune bedding. This is seen in both outcrop and core and derived from the continuous dip-meter logs of many North Sea wells by plotting the poles to the bedding attitudes on polar nets. Palaeowind directions have also been deduced from the dip-meter logs of wells drilled in the Northern and Moray Firth Basins. In general, they indicate winds that blew in a direction opposed to those of the Southern Basin. Thus an area of high barometric pressure seems to have been located over the Mid North Sea High. When the bedding attitudes in a well are roughly unidirectional, an origin on a transverse dune is normally indicated. With some wells, the indicated palaeowind direction is regionally anomalous. In many cases this can be rectified if the well is presumed to have drilled down through one flank of a seif dune. The indicated palaeowind is thus changed by up to 90° and then commonly fits the regional pattern. These early Permian desert basins were smaller and closer to the equator than the modern Sahara. Their location in the centre of a continent between the Caledonian and Variscan mountain ranges suggests the analogy of a more tropical equivalent of the Central Asian Takla Makan Desert.

Organofacies and Early Maturation Effects in Upper Jurassic Sediments From the Inner Moray Firth Basin, North Sea

Summary A study of oil source rock characteristics and the degree of organic maturity has been carried out on a thick succession of Upper Jurassic sediments from the inner part of the Moray Firth Basin. The sequence, which attains a thickness of up to 1000 m, consists of organic-rich mudstones and silty shales with periodic intercalations of turbidite sands. Samples representative of finer grained lithologies covering a range of present burial depths from 800 to 2400 m were selected from four exploration wells, one each in Blocks 12/21 to 12/24, immediately northeast of the Beatrice Oil Field. Kerogen preparations from all samples are dominated by amorphous algal sapropel, but contain appreciable coarsely particulate terrigenous material originating from vascular plants and probably introduced into the restricted marine basin of deposition by distal turbidity currents. This organofacies is highly rated as a potential oil source, but maturation levels are consistently low within the drilled wells. Independent maturation-specific parameters, including vitrinite reflectance, sporomorph colour, solvent extract and extractable hydrocarbon:organic carbon ratios and the carbon preference index of nC 21 -nC 33 alkanes indicate immature organic matter at depths above 2000 m. A pronounced increase in extract ratios below 2000 m indicates approach to the oil generation threshold at the base of the deepest section. Initially high CPI values in the uppermost samples (except where migrated oil is present in Block 12/23-1) decrease steadily with burial. Significant amounts of steranes and triterpanes are present in the sediment extracts and have been identified by combined gas chromatography-mass spectrometry (GC/MS). A C 28 pentacyclic triterpane (17αH,18αH,21βH-28,30-bisnorhopane) was identified in unusual abundance. Isomerization occurs at one or more chiral centres in the steranes, rearranged steranes and hopane type pentacyclic triterpanes in response to increased burial and temperature (Mackenzie et al. 1980). These changes have been assessed in terms of relative abundances of certain specific isomers and compared with abundances in other basinal sequences with known maturational trends. A consideration of all parameters places the onset of intense oil generation somewhat below the base of the deepest section (Block 12/24-1) and sets limits on the maximum relative uplift experienced by the other sections.

Structural outline and development

The Central Graben is a broad, complex trough with a long history of differential subsidence. It was probably initiated in the Permian and was controlled by major rifting during the Mesozoic. To the south in the Dutch sector the trough is divided into two parts. From here it passes northwards and divides the southern North Sea Basin into the Anglo-Dutch Basin and the Northwest German Basin. It also separates the Mid North Sea High from the Ringkøbing-Fyn High. These highs form broad, east-west trending, relative stable ridges. The further continuation of the Central Graben is to the northwest, towards the centre of the North Sea, where it passes into the Viking Graben and the Moray Firth Basin at about 58° N. Where the Central Graben divides the two major highs, there is an elongate central narrow horst, the Dogger High, which is the southernmost of a row of mid-Graben highs. Both sides of the Graben are clearly defined by normal rotational faults that were intermittently active from Triassic to Early Cretaceous times.

Recent excavations at the Greensand locality of Moreseat, Grampian Region

Synopsis Recent excavations at the Greensand locality of Moreseat, Grampian Region are described. The Greensand is thought to occur in several small, isolated, erratic masses. The erratics were probably derived from the Moray Firth basin and may have been glacially transported to the site prior to the Devensian cold stage.

Development of basins in the Inner Moray Firth and the North Sea by crustal extension and dextral displacement of the Great Glen Fault

Reflection seismic data provide evidence that Mesozoic dextral movements along the Great Glen Fault line have had an important influence on the development of the Inner Moray Firth Basin. Geophysical evidence further indicates that deep structure beneath the inner basin is dissimilar to that beneath the outer part and Viking and Central Grabens in the North Sea. Tectonic development of the inner basin can nevertheless be fitted into a pattern of North Sea extensional movements which led to the formation of the graben system with which the major North Sea hydrocarbon resources are associated.

Interpretation of refraction experiments in the North Sea

Before 1977, only three long-range seismic refraction profiles had been shot in the North Sea Basin, with somewhat inconsistent results in terms of a description of the Mohorovicic discontinuity (Moho). In the summer of 1977, the Marine Group of Cambridge University fired three refraction lines with the use of pull-up, shallow-water seismometers, the longest reversed profile extending for 400 km along the 0.5° E meridian from east of the Shetland Islands to the latitude of Dundee. Although records varied in quality, a time term interpretation of the results was made with the use of detailed velocity-depth information supplied by the oil industry. This interpretation indicates that there is an anticlinal form to the Moho beneath the deepest sediments of the Moray Firth Basin, as demanded by gravity data from the area. It is further suggested that the seismic evidence supports an extensional model to explain the origin of the North Sea Basin.

Development geology of the Piper Oilfield

The Piper Oilfield lis in the UK Block 1517, 125 miles northeast of Aberdeen, Scotland. The field is situated on a shelf south of the East Shetland platform, and near the eastern end of the Moray Firth Basin. The field was discovered in January 1973 from a seismicly mapped structure and confirmed as a major oilfield during the year with five appraisal wells and one exploratory well. A steel platform with 36 well slots and space for two drilling rigs was centrally located over the field in 474 ft. of water in June, 1975, and made ready for production drilling by October 10, 1976. Commercial production was established December 7, 1976, when the P1 well came on stream at more than 30 000 b/d. Production is currently 290 000 stb/d of 37°C API, low sulphur oil and original recoverable reserves are estimated to be 618 million barrels. Production is from the Upper Jurassic Piper Sandstone, a high-energy, marginal marine and marine, shallow, shelf sandstone with gross thickness of 165–454 ft. The field comprises three parallel, tilted fault blocks on the north edge of the Witch Ground Graben. Blocks I and II cover 7149 productive acres and have oil columns of 1312 ft. from 7200 ft. subsea to a common oil-water contact at 8512 ft. subsea. Block III to the southwest borders the Witch Ground Graben and contains a small accumulation with separate oil-water contact at 9199 ft. subsea. A combination of favourable geological and engineering conditions together with extensive use of seismic data before and during development drilling has resulted in high production rates and the need for only one centrally located platform to maximize the recoverable reserves from Piper oilfield.

THE PROVENANCE AND DISTRIBUTION OF THE PALAEOCENE SANDS OF THE CENTRAL NORTH SEA

A study of the detrital heavy minerals from Palaeocene sandstones of the central North Sea basins has revealed that variations exist which cannot be explained in terms of varying conditions either during or after deposition, and therefore reflect the influence of distinct source areas. Four sand bodies have been defined on a mineralogical basis, two of which occur in the Central Graben and southern Viking Graben, derived from the E. Shetland Platform, the other two being developed in the Moray Firth area, derived from the Scottish landmass. These sand bodies, when related to the existing lithostratigraphic framework, define four phases of basin subsidence, with the sand depocentre alternating between the Central Graben and the Moray Firth basin. This oscillation in basin subsidence, the association with volcanogenic sediments and the apparent basement control on distribution of sands in the Moray Firth indicate a degree of tectonic control hitherto undescribed for the Palaeocene of the area.Studies of sandstones in or around the inferred source areas have revealed that the metamorphic basement was the major contributor to the sands of the Moray Firth, rather than the pre‐existing sandstones of Devonian, Permo‐Trias or Jurassic ages which occur on the margins of the Firth. Likewise the Old Red Sandstone or Permo‐Trias sandstones of the East Shetland Platform are not suitable source rocks for the sands of the Central Graben and in this case it has been necessary to postulate the existence, at least until the end of Palaeocene times, of Carboniferous sands on the Platform. Such sands in the central North Sea have been shown to possess a mineralogy not dissimilar from that of the Palaeocene sands in question.

Piper Oil Field: ABSTRACT

The Piper field lies in UK block 15/17 near the eastern part of the Moray Firth Basin, 125 mi northeast of Aberdeen, Scotland. The field was discovered in December 1972. Five appraisal wells and one exploratory well were drilled in 1973. A steel platform with 36 well slots and space for two drilling rigs was centrally located over the field in 474 ft of water in June 1975, and readied for production drilling by October 1976. Production is from the Upper Jurassic Piper Sandstone, a high-energy, marine sandstone with gross thickness, 177 to 453 ft (56 to 138 m); net sand, 132 to 378 ft (40 to 115 m); net oil sand, 132 to 296 ft (40 to 90 m); average net oil sand, 160 ft (49 m); average porosity 26%; permeabilities 200 to 1,200 md in lower energy bioturbated sands, 2,000 to 0,000 md in higher energy sands. The reservoir is sealed by Kimmeridge shale over most of the field and by Upper Cretaceous marlstones along some fault scarps. The main area of the field, a gently folded fault block dipping 5° northeast and a downthrown northwest-southeast fault block, covers 6,300 acres (2,550 ha.), has a common oil-water contact at 8,512 ft (2,594 m) subsea, and a gross reservoir column 1,300 ft (396 m), which is 7,200 ft (2,195 m) subsea to the oil-water contact. A small accumulation on a parallel fault block on the southwest has a separate oil-water contact at 9,199 ft (2,804 m) subsea. The P1 production well spudded October 10, 1976, established commercial production December 7, 1976 at more than 30,000 B/D, restricted by 5½-in. tubing. The P7 well complet d in April 1977 produced more than 50,000 BOPD, restricted by 7-in. tubing. Twenty-four wells have been drilled, four as water injectors to support an active water drive. Production is 300,000 BOPD and recoverable reserves are estimated to be 700 million bbl. Extensive use of seismic data and excellent cooperation by partners in the consortium and the United Kingdom regulatory bodies allowed maximum use of production and new well data to improve subsequent development. End_of_Article - Last_Page 489------------

Petroleum Exploration and Production in Europe in 1975

Large-scale oil production from North Sea fields started late in 1975, but production elsewhere in western and southern Europe changed little from the 1974 rate. A large gas field in the Dutch North Sea area went on production and other fields were being developed actively. A major oil discovery was made at Brae in the Viking graben near the center of the North Sea east of northern Scotland. Other new fields were found in the Viking graben and the Moray Firth basin and major extensions were drilled to discoveries of previous years. Two exploratory wells off the east coast of Spain tested large volumes of oil. In the Molasse basin of Austria there was an important discovery of oil and another of gas. A new gas field was found in the Molasse basin in southern Germany. In It ly there were 7 gas discoveries and a large reservoir of low-gravity oil was found in the Adriatic. New fields, probably small size, were found onshore in France, The Netherlands, and Sweden, and a 1973 oil discovery in southern England was confirmed and extended. In the Soviet Union production of crude oil and condensate was 9,820,000 b/d and of gas 27 Bcf/d. The large increase in Soviet oil production was at the expense of heavy withdrawals from a limited number of large fields, and there was concern about adequacy of future supply. Discoveries of oil in Paleozoic rocks of the floor of the southern West Siberian basin have encouraged extensive exploration in that region. Among widespread gas and oil discoveries in different parts of the USSR, deeper pool gas discoveries in the western Caspian at 16,500 to 17,500 ft (5,029 to 5,334 m), and gas discoveries and extensions in the Sea of Azov were of special interest.

The stratigraphy of the Callovian and Oxfordian stages (Middle-Upper Jurassic) in northern Scotland

Synopsis Outcrops of Middle-Upper Jurassic rocks in northern Scotland are restricted to two sedimentary basins. In the east exposures at Brora (Sutherland) and Balintore (Ross-shire) are part of the Moray Firth basin. In the west major exposures at Staffin and in Strathaird (Isle of Skye) belong to the Minch basin. A formal lithostratigraphy is erected with five formations and twenty-six members, which have been correlated with the standard ammonite zone. Each basin presents a pair of sections, with thick sandy onshore sequences at Brora and Strathaird and condensed argillaceous offshore sequences at Balintore and Staffin. The two onshore/offshore localities show marked facies similarities, but are affected by different transgressions in the Oxfordian. A new species of Longaeviceras is described. It is the first authenticated record of this genus from the Oxfordian.

Structure of the Crust Beneath the Caledonian Foreland and Caledonian Belt of the North Scottish Shelf Region

Summary This paper presents those results from the sea-to-land North Atlantic Seismic Project of 1972 which apply to the North Scottish shelf region. Time-term analysis based on first arrivals yielded P, of 6.1050.15 km s-', P* of 6.4850.06 km s-' and P, of 7.9950.02 km s-'. The presence of a P* refractor yielding first arrivals distinguishes the northern British crust from that south of the Caledonian belt. Beneath the Caledonian foreland, the P refractor varies in estimated depth between 2 and 16 km and its depth correlates with the Bouguer anomalies; it most closely approaches the surface beneath a 90 mgal Bouguer anomaly high west of the Shetland Islands, and is interpreted in terms of widespread occurrence of Lewisian granulites beneath the region. The Moho beneath the foreland occurs at a remarkably uniform estimated depth of 26+2 km. The P* refractor has been identified beneath the western part of the Caledonian fold belt and beneath the Moray Firth, and may occur more extensively. The crust beneath the fold belt is of the order of 20 per cent thicker than beneath the foreland, except beneath Moray Firth where the crustal thinning to the present estimate of about 23 km may have occurred during the post-Caledonian formation of the Moray Firth basin.

Petroleum Exploration and Production in Europe in 1974

Oil production continued to decline in the older fields onshore in Europe, and large-scale production from North Sea fields still awaited completion of producing facilities. Gas production increased in The Netherlands and in the British North Sea, but was near its peak from present producing fields. There were 2 giant oil discoveries in Jurassic sandstones in the northern North Sea, Statfjord in the Norwegian area and Ninian in the United Kingdom sector. A series of still mostly unevaluated oil and gas condensate fields was found in the United Kingdom sector, including 4 oil discoveries in the Moray Firth basin east of Scotland. Oil and gas fields were found in the Norwegian and Dutch areas, and a gas discovery in German waters. There was active exploratory drilling on th Atlantic shelf west of the Shetland Islands, and oil shows were reported in one well. Oil was discovered for the first time in Greece, in the northern Aegean Sea. Two wells off the coast of southern Ireland flowed oil. In Italy the Melossa field, discovered in 1973 northeast of Milan, proved to have major gas and oil reserves. An oil discovery was made on the Adriatic coast of Italy. Wells on the Swedish Island of Gotland pumped small volumes of oil from the lower Paleozoic. Minor oil and gas discoveries were made in France, and there were 4 gas finds in Germany, one of them apparently important. In the Soviet Union production of oil and condensate was 9,185,000 b/d and of gas 25.2 Bcf/d. Production from the West Siberian basin increased 40%, and most of this was from the Samotlor field. A new-pool discovery in the Jurassic of the Salym field of western Siberia proved giant-size oil reserves. Oil was found in the Paleozoic in 2 new West Siberian fields. Gas discoveries were made in central and northwestern Siberia, Middle Asia, and offshore in the eastern Caspian Sea, and new oil fields were found in the western Caspian.

Note on the occurrence of traces of heavy metals in the sandstones of the Moray Firth Basin

Some months ago in an inquiry into the possible cause of the precipitation of peroxide of manganese in the dark stains seen in some sandstones, and typically at Newton in the U.O.R. division of the Elgin sandstones, I was surprised to find that in addition to the oxide of manganese these stained areas showed notable traces of copper as well as of nickel and cobalt. Other small nodules occurring in a Triassic sandstone overlying the Rosebrae division of the U.O.R. rocks near the Old Hospital Quarry were found to contain, in association with a relatively greater proportion of the manganese oxide, very much larger proportions of the bases indicated—CuO ·12%, oxides of nickel and cobalt ·69%, with the addition of 1·68% of lead calculated as PbO2 or PbS. As these occurrences were ascribed to secondary local infiltration it was naturally inferred that the surrounding sandstones would if examined probably also show traces of the same metals. Accordingly determinations of the amount of copper oxide, and also of the nickel and cobalt oxides conjointly in a series of specimens (sixteen in all), ranging in time from the L.O.R. of Tarradale, Culloden, and Spey Bridge through the U.O.R. division to the Triassic rocks of Cuttieshillock, Spynie and Cummingston have been made, and in not a single specimen has the copper oxide been found absent, while of the nickel and cobalt, traces of at least one and not improbably both have been found in every instance. The difficulty of effecting a separation with

XXI.—The Old Red Sandstone Volcanic Rocks of Shetland

Perhaps the most interesting feature connected with the Old Red Sandstone formation in Shetland is the evidence of prolonged volcanic activity in those northern isles. The great development of contemporaneous and intrusive igneous rocks, which gives rise to some of the most striking scenery in Shetland, is all the more important when compared with the meagre records in the Lower Old Red Sandstone of Orkney and the Moray Firth basin. Not till we pass to the south of the Grampians do we find evidence of a far grander display of volcanic action during this period, in the sheets of lava and tuff in the Sidlaws and Ochils and in the great belt stretching from the Pentlands south-westwards into Ayrshire. The relations of the Shetland igneous rocks are admirably displayed in the various coast sections, especially in the mural cliffs of Northmavine and some of the Western Islands. From these records, though they have been subjected to much denudation, it is possible to construct a tolerably complete sketch of the volcanic history of this formation, as developed in that region.