bluuebunny/crossref_metadata_2025 huggingface dataset:
Revision of the geology of the Dunlewy and Crockator areas, Co. Donegal
Authors: RICKARD MICHAEL JOHN
Published: December 2007

T
he discovery
that the Lackagh Quartzite correlates with the Ards (Errigal) Quartzite (Pitcher & Shackleton 1966) means that the structure in the meta-sediments adjacent to The Main Granite at Dunlewy, as deduced by
Rickard (1962)
, is incorrect. Revision of the mapping (Fig. 1) shows that the structural arrangement can be interpreted in conformity with the new stratigraphical concept. All the formations of the Greeslough Succession (Fig. 1B) are attenuated in this district and the structure is complicated by the Dunlewy crossfolds (
Rickard 1962
). Several black pelitic layers were previously included in the Creeslough Formation but a consistent structural model can now be made by assigning these to the Ards Black Pelite Formation. Similarly the several limestone bands reduce to two main members, one within the Ards Pelites and the other close to the junction of the Ards and Greeslough Pelites—the latter representing the Altan Limestone Formation.

Southwest of Dunlewy Lough black pelites surround the outcrop of the Greeslough Pelites defining an anticline, on the southern flank of which the Ards Quartzite is reduced to a very narrow outcrop of flaggy quartzites, previously mapped as Lackagh. Within this quartzite an interlayered pelite and flaggy quartzite unit is now recognized (Fig. 1): this resembles the Falcarragh Pelite Formation at its closest outcrop to the north west. There must be a tight syncline here in which the intervening Clonmass Group has been sheared out, as elsewhere in the Dunlewy crossfolds (
Rickard, 1962
).

The structure that is now deduced is that of two
Systematics in palaeontology
Authors: GEORGE THOMAS NEVILLE
Published: December 2007

A ‘natural’ taxonomic system, inherent in organisms that themselves demonstrate their ‘affinity’, is to be recognized perhaps only in the biospecies. The concept of the biospecies as a comprehensive taxon is, however, only notional amongst the vast majority of living organisms, and it is not directly applicable to fossils. ‘Natural’ systems of Linnaean kind rest on assumptions made
a priori
and are imposed by the systematist. The graded time-sequence of the lineage and the clade introduces factors into a systematics that cannot well be accommodated under pre-Darwinian assumptions or be formulated by a Linnaean nomenclatural method.

The fossil evidence of ‘affinity’ is best served by a system of classes defining intrinsic relationships that are phylogenetic. Multiple demic variants, clinal bioseries, variable rates of evolutionary change, pulses of biased selection pressure in expanded and restricted palaeodemes, and permutations of character-expression in the evolutionary plexus impose a need for a palaeontologically-orientated systematics under which (in evolutionary descent) could be subsumed the taxa of the neontological moment.

Environmentally controlled morphs, biofacies variants, migrating variation fields, and typological segregants are sources of ambiguity in a distinction between phenetic and genetic fossil grades. Trends in variants are not to be confused with trends in transients; and sequential demes may (in time and space) show trend reversals as a sign of nongenetic (phenetic) selection. The morphospecies of the local palaeodeme is then to be distinguished from the holomorphospecies of the lineage segment, both in kind and in taxonym; and the association of variant morphotypes in a unitary deme is no justification for a splitting of the deme into several morphospecies.

Criteria of cladal disjunction are multiple. They may rest in one or a few ‘differential’ characters, or (in a ‘numerical’ taxonomy) on an Adansonian equal-weighting of ‘all’ characters. A consequence is to impose on an inferred phylogeny taxonomic incompatibilities deriving from contrasted interpretations of homology and homoeomorphy. Clinal disjunction as an incipient sign of cladal branching presents other problems in nomenclature and in the definition of taxon-range. Accelerated and retarded rates of bioserial change in sub-parallel lineages further complicate systematics notably in mosaic evolution. A basic distinction between Linnaean (morphotypic) and evolutionary systematics rests in the relevance of the question that asks whether the class determines the characters or the characters the class.
THE SILURIAN-DEVONIAN BOUNDARY—
Authors: Westoll T. S. , Shirley J. , Dineley D. L. , Ball H. W.
Published: December 2007

For over a century the position of the Silurian-Devonian Boundary has excited controversy and the problem continues to exercise the Committee on the Silurian-Devonian Boundary instituted by the International Commission on Stratigraphy. There has been vigorous activity to examine and adopt a new horizon at which to draw this boundary. Little enough has been said to maintain the value, usefulness and claims of the boundary that has served so long. While we do not wish to stand in the way of an innovation that may, insofar as recognised graptolite zones are used, be better than that which we have used so far, we question whether British geologists have assessed adequately what is involved in the recommendation of the British Silurian Subcommittee. The matter was indeed raised in a letter to the Editor of the Geological Magazine (March–April, 1969, pp. 215–216) by P. T. Warren on behalf of the Institute of Geological Sciences. Warren said ‘. . . we shall, as a matter of policy, in the immediate future at least, continue to use the Ludlovian-Downtonian boundary as the Siluro-Devonian boundary.’ We offer the following points for serious consideration and we stress that it is more important for British geologists to deliberate fully a recommendation before endorsing it, than to give unqualified assent when indeed there are important grounds for hesitation.

Despite the Silurian Committee’s conclusion that the Downtonian stage be included within the Silurian system, there appear to the undersigned to be good reasons for retaining the base
Geology and society in Britain—the need for a comprehensive appraisal
Authors: BASSETT DOUGLAS
Published: December 2007

One hundred and fiftyyears ago, when the major qualitative changes initiated during the so-called 'Heroic Age of Geology' were beginning to be appreciated and to take effect, it was possible for one man to have a reasonably comprehensive grasp of the state of geology in this country. Nowadays, however, individual geologists are unable to keep abreast of the developments in their own field let alone keep track of the rapidly changing structure of geology in general, and of its relations with other sciences and with society.

Considerable effort is, of course, being made by various individuals, institutions and societies to keep abreast of the exponential growth of geological literature by providing bibliographies, abstracts and reviews. And although it is becoming increasingly difficult 'to keep up with keeping up,' there is definite evidence of co-operative effort between scientists and librarians in tackling the problem.

Similarly, statistical and other surveys are being carried out regarding the distribution of geological manpower as part of the triennial manpower surveys of persons in employment with qualifications in engineering, science and technology and also of the place of geology in education, in industry and in other sections of society. These assessments are, however, being carried out by a diversity of bodies and the results commonly appear in publications which either have restricted distribution, or are little known to practising geologists. Any one individual geologist has, therefore, little chance of appreciating the overall picture. Because of this, I wish to make three inter-related suggestions :–– that
Processes of geological evolution
Authors: SYLVESTER-BRADLEY PETER
Published: December 2007

T
he heart
of geology has always been represented by a synthesis of diverse disciplines. In the early days of our science, it was from this synthesis that the great historical pageant of the last four thousand million years was built up. A hundred years ago, the generalisations of geology culminated in the contribution they made to the history of the Earth. It seemed then that the goal of every geologist, whatever his discipline, was to add a page, a chapter or an appendix to a record of events that embraced everything from the origin of the Earth to the dominance of man.

But this is no longer the case. Now it is not a record of events that lies at the heart of our science. Our curiosity is busy with another question. It is a question set by the history itself. We can see that we are not dealing with an arbitrary repetition of cycles. There is an overall, inexorable, dynamic change relentlessly driving forward. The Earth is changing in nature, and the synthesis that we are looking for now is one that explains that change. What processes are at work? How far is geological evolution a part of a more general process, affecting all planets? Can geological processes be grouped together as a special case of planetary evolution?

The concept of planetary evolution is opposed to that of a 'steady state'; it is not opposed to the more sacred principle of uniformitarianism. If the Earth, in not opposed to
Letters concerning the Cambrian-Silurian controversy of 1852
Authors: CRAIG GORDON YOUNGER
Published: December 2007

S
ir
R
oderick
I
mpy
Murchison died 100 years ago. One of the last political acts of his busy life was to provide an endowment of £6,000 to the University of Edinburgh in 1870 so that a Chair of Geology might be founded. At the same time he ensured that his protégé Archibald Geikie was appointed to the post in 1871. Among Geikie's correspondence, now in the library of the University, are letters on the notorious Cambrian-Silurian controversy involving Murchison and Council members of the Geological Society of London. The letters followed the publication of Sedgwick's paper on the classification and nomenclature of the Lower Palaeozoic rocks of England and Wales in the Quarterly Journal of the Society in 1852. For good measure there is also a document by Murchison setting out his considered views on the controversy and an earlier letter written but never sent to Sedgwick in which Murchison comments candidly on his mother-in-law and his religious creed.

The main story spans the life of two Councils of the Geological Society—those of 1851 and 1852—but the events themselves are crowded into the period February to June 1852. The Council for 1852 consisted of: D. T. Ansted W.J. Hamilton (Secretary) Lt.-Coh Portloek R. A. C. Austen J. D. Hooker S.P. Pratt J. J. Bigsby W. Hopkins (President) J. L. Prevost J. S. Bowerbank L. Horner A.C. Ramsay C. J. F. Bunbury C. Lyell D. Sharpe E. Forbes G.A. Mantell W.W. Smyth G. B. Greenough R.I. Murchison

Most had served
The Devonian successions in the Padstow area, North Cornwall
Authors: GAUSS GARRY ALLAN , HOUSE MICHAEL ROBERT
Published: December 2007

Two different successions of Middle and early Upper Devonian rocks are described from the north coast of Cornwall around Padstow. These have been named the Trevone and Pentire successions. The former is seen especially south and west of Camel Estuary and is characterised by a tectonic style of overturned or recumbent folds facing north. The Pentire succession seen north and east of the outer part of the Camel Estuary shows greater tectonic complexity with a southward facing recumbent fold style. A correlation of these successions with each other has been attempted and faunas enable correlation with the international scale. Some interpretation of the depositional environments is given and estimates of the thickness of units have been made. The axis of the St. Minver synclinorium of the literature approximately separates the two successions.

The Trevone Succession in order of deposition comprises Trevose Slates (upper Eifelian and Givetian and at least 490 m thick), Marble Cliff Beds of turbiditic limestones (lowest Frasnian and at least 67 m thick), Longcarrow Cove Beds of grey slates with agglomerates and tufts (probably low Frasnian and perhaps as much as 300 m thick), Merope Island Beds of goniatite-bearing grey slate (mid Frasnian and some 60 m in thickness), Harbour Cove Slates of grey slate with purple bands and many goniatite beds (mid Frasnian of about 580 m thickness), Polzeath Slates of colourful purple and green slate (presumed late Frasnian and earliest Famen-nian seen to 120 m).

The Pentire Succession shows closely similar Trevose Slates and Polzeath Slates, the latter seen to some 200 m. Marked differences are shown by the intervening sequence which appears complete and comprises the Pentire Pillow Lava Group some 450 m thick, comprising slates, pillow lavas, volcanic tilloids and tufts, the Pentire Slates some 340 m thick, the Gravel Caverns Conglomerate, a remarkable group some 90 m in thickness of slates, mud flow conglomerates and volcanics with mid Frasnian goniates. The latter is overlain by the Polzeath Slates.

Tectonic juxtaposition of two essentially deep water argillite successions is invoked to explain the present proximity of the two differing successions. Some comparisons are made with equivalent successions in South Cornwall and South Devon.
The topography of the seafloor around Orkney and Shetland and in the northern North Sea
Authors: FLINN DEREK
Published: December 2007

The construction of a bathymetric map of the continental shelf of the British Isles around Orkney and Shetland and extending east to the Norwegian Trench and as farsouth as Aberdeen is described. The map is based on echo traces made by a large number of ships in the course of their duties and also on all available published charts and much unpublished bathymetric data. The map is presented together with maps showing the nature of the bottom and the roughness of the bottom based on information obtained during the construction
of
the bathymetric map.

The origins of the various features appearing in the maps are discussed. It is shown that in the Orkney and Shetland area broad flat bottomed deeps coincide with basins of young sediments (post-Devonian and probably Mesozoic or Tertiary) and are probably of glacial origin. In the North Sea deeps are mostly very narrow and elongate and these have been interpreted as tunnel-valleys formed beneath an ice front. They are arranged in an arcuate belt partly surrounding the deepest part of the North Sea where there is a patch of mud. This mud was probably deposited from the water flowing out from beneath the ice where it was formed into a lake. It is possible that a submarine canyon on the edge of the Norwegian Trench to the east of the mud patch is the overflow channel for this water.
A classification of climbing-ripple cross-lamination
Authors: ALLEN JOHN R. L.
Published: December 2007

C
limbing
-
ripple cross-lamination
,
Sorby’s (1859, 1908)
ripple-drift bedding, is an important and significant sedimentary structure resulting from the action of unidirectional currents. The importance of the structure lies in its worldwide distribution and frequent occurrence in such diverse sediments as river channel and levee sands and in turbidity current deposits. Its significance is that, of all sedimentary structure, it stands alone in giving information on short-term rates of sediment deposition (
Sorby 1908
;
Kuenen 1967
;
Walker 1969
;
Allen 1970
, 1971
, 1972
). Hence the study of this structure may lead to a deeper understanding of aspects of the character of past events—river floods and turbidity currents—of an intrinsically brief and catastrophic nature.

This goal will not however be achieved until the nature of climbing-ripple cross-lamination is clearly perceived and defined within the framework of an unambiguous field classification. The most widely used existing classification of the structure is now recognized to be confused, because some of the criteria adopted for the definition of its categories relate to the individual cross-laminated set (and the set with its immediate neighbours) perceived at some station in a coset, whereas others properly describe the coset of which the individual cross-laminated set is generally a very subordinate part. Set and coset are here used in the well-known sense of McKee & Weir (I953). The consequence is that aspects of the structure at the level of the set and its immediate neighbours are not sharply enough distinguished from aspects of the structure at the level of the
Major structures in Morar and Knoydart, NW Scotland
Authors: POOLE ALAN B. , SPRING JOHN S.
Published: December 2007

The Moine and Lewisian rocks of Morar and Knoydart on the west coast of Scotland have been involved in at least three major deformation phases. The earliest folds, in which Lewisian rocks form the cores of anticlines, and the youngest Moine formation the cores of synclines, are perfectly isoclinal. The second phase has produced a major recumbent fold, essentially a westward closing antiform, which refolds the previous structural succession. This recumbent fold, which is termed the Knoydart Fold, is underlain by a clearly recognized slide of approximately the same age which is called the Knoydart Slide.

It is proposed that the axial plane of the Knoydart Fold is cut at a small angle by the slide, so that the fold and its closure have two main outcrops, one below the slide in the west and another above the slide in the east. The whole assemblage is finally refolded into the more open Morar Antiform in the west and the Ben Sgriol Synform in the east. The proposed structure implies that the Lewisian outcrops around the Morar Antiform are on the lower limb of the Knoydart Fold and root eastwards. These rocks may be traced round the hinge of Knoydart Fold and are represented on the upper limb by the Lewisian in east Morar, which consequently roots westwards.
Interglacial coleoptera from Bobbitshole, Ipswich, Suffolk
Authors: COOPE G. RUSSELL
Published: December 2007

An assemblage of twenty one named species of Coleoptera is described from the type locality of the Ipswichian interglacial at Bobbitshole, Suffolk. This assemblage can be assigned to the boundary between pollen zones
e
and
f
of the interglacial. All species live today in western Europe. They indicate that the deposits were laid down in a eutrophic lake or pond with a rich peripheral reed swamp. The climate of the times was considerably warmer than that in the area at the present day with average July temperatures of about 20°C; about 3°C above those for southern England today. There is no evidence of increased climatic continentality. Compared with other interglacial faunas, this assemblage differs markedly from those of the Hoxnian interglacial but bears a striking resemblance to the Ipswichian assemblage from the excavations in Trafalgar Square.
The Oxfordshire Coalfield
Authors: DUNHAM KINGSLEY G. , POOLE EINAR G.
Published: December 2007

Although the presence of Upper Coal Measures under the Mesozoic rocks around Burford has been known for nearly 100 years, productive Westphalian was proved for the first time in this area by the IGS Apley Barn borehole, near Witney, where Upper Carboniferous strata were entered at 250–19 m. Two further boreholes, at Steeple Aston and Withycombe Farm subsequently drilled suggest that the concealed coalfield possibly has an area of 450 sq miles. The tonnage of coal could be of the order of 10 x 10
9
. The succession commences in the zone of
Anthraconauta tenuis
and correlations with the Somerset-Bristol coalfield, and with the Halesowen and Keele groups of Warwickshire are suggested. Intrusive basalts, dated at 298 m.y. and basalt-breccias were found at Steeple Aston. The pre-Carboniferous rocks encountered throw some light on gravity anomalies in the Cotswolds; the Banbury-Shipston 'high' may be a buried anticline of Silurian, while the Steeple Aston 'low' is correlated with thick Old Red Sandstone.
Alpine-type structures in the Rhodesian basement complex at Selukwe
Authors: STOWE CLIVE W.
Published: December 2007

The Rhodesian Archaean Craton consists of greenstone schist belts tightly folded between gneiss domes. The Selukwe Schist Belt, situated near the centre of the craton, consists of mainly Sebakwian Group greenstones, ultra-mafics and sediments, older than intrusive 2900 m.y. tonalities. It appears to be part of an imbricated and overturned lower limb of a large recumbent fold, resting allochthonously on a gneissic basement. Four main tectonic slices, separated by mylonite shear zones were recognized. The inverted succession together with the shear zones were refolded during two subsequent tectonic episodes, before being arched and tilted by intrusion of the tonalite diapir in the southeast.
The zonal pattern of regional metamorphism in the Scottish Caledonides
Authors: WINCHESTER JOHN A.
Published: December 2007

The petrology of analysed Moine calc-silicate rocks enables a metamorphic zonal map of the Moines to be drawn. Correlation with pelite isograds in the Dalradian has permitted the production of a zonal map of the entire Scottish Caledonide Belt. The complex zonal pattern in the Moines is attributed partly to the interaction of different metamorphic events, which brought about widespread retrogression and apparent metamorphic inversion, and partly to post metamorphic folding of isograde surfaces.
Field observations of edge waves and their effect on beach material
Authors: HUNTLEY D. A. , BOWEN A. J.
Published: December 2007

Observations of wave motion are described, particularly of the horizontal particle velocities, up to a maximum of 25 m from the shoreline on Slapton Beach, Start Bay. For the first time on a natural beach, the observed velocities reveal directly the presence of short period edge waves, modes of wave motion trapped to the shoreline by refraction. These edge waves occurred at the first subharmonic (σ/2) of the incident wave frequency σ, and their exponential decay in amplitude with distance from the shoreline was consistent with edge waves of mode number zero with a longshore wavelength of 34
±
6m. The implications of these observations are discussed in the light of recent laboratory experiments and theories of edge wave generation, and a possible swash interaction mechanism for generating subharmonic wave motion on Slapton beach is described.

A steady longshore current prevented these subharmonic edge waves from forming cuspate or crescentic features in the nearshore beach material. Small shoreline cusps observed on Slapton beach on other occasions were consistent with edge waves at the frequency of the incident waves themselves.
Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland
Authors: WALKER GEORGE P.L.
Published: December 2007

The remarkable swarm of inclined basic intrusive sheets found in the deeply dissected part of SE Iceland is believed to constitute part of a widespread layer which, in other parts of the country, occurs below sea level as the 6.35 km s
−1
crustal layer revealed by seismic refraction studies. A simple mechanism for the generation of the sheet swarm is proposed, based on the contrasted density gradients of crust and uprising magma: basic magma rises to the surface when its density is everywhere less than the bulk density of the rocks it cuts, otherwise it is often diverted laterally to form an intrusive sheet where its density equals that of the country rock. Once initiated, density relations in the crust are such that the swarm is strongly self-perpetuating in nature. It is believed that more than half of the uprising magma in Iceland has been so diverted to form the sheet swarm. One corollary is that the crust in Iceland “filters” the magmas entering it so that only the lighter or those which rise at a high volumetric rate succeed in passing through to the surface. Confluent sheet gabbro intrusions may develop when the frequency of uprise of magma batches is high. Sheet swarm cupolas or perched swarms also occur in central volcanoes, in which the low-density acid volcanic rocks “capture” uprising magmas.
Rb-Sr whole rock isotopic studies of Lewisian metasediments and gneisses in the Loch Maree region, Ross-shire
Authors: BIKERMAN MICHAEL , BOWES DONALD R. , VAN BREEMEN OTTO
Published: December 2007

Fifty-three whole rock Rb–Sr isotopic analyses are reported on two metasedimentary schist and four gneiss units in the Lewisian of the Loch Maree region. Isochron dates from the Gairloch metasediments–Ard gneisses (1980 ± 50 m.y.) and the Loch Maree gneisses (1965 ± 100 m.y.) date the main phase of metamorphism of the Laxfordian episode at 1975 ± 75 m.y. A 1745 ± 160m.y. whole rock isochron date on the Carnmore kyanite–biotite gneisses can be related to late tectonic pegmatite intrusions. Whole rock data points from the quartzofeldspathic gneisses from the Carnmore district do not define an isochron. A 1500 ± 95 m.y. isochron date for metasediments of the Loch Maree Group is interpreted in terms of final closure, during epeirogenic uplift, after a 200–300 m.y. period of isotopic exchange below an impervious cap of tectonically overthrusted hornblende schist and quartzofeldspathic gneiss.

Initial
87
Sr/
86
Sr considerations indicate both a crustal history for the gneisses of the Loch Maree and Carnmore districts going back to 2.7–2.8 b.y. and deposition of the Gairloch metasediments and Loch Maree Group after 2.2 b.y. ago, presumably unconformably on the older metamorphic complex.

The Laxfordian orogenic cycle is defined, in the classical stratigraphic sense, to consist of a depositional episode 2.2–2.0 b.y. ago, an orogenic episode 2.0–1.7 b.y. ago and an epeirogenic episode 1.7–1.5 b.y. ago. There are marked similarities in the Laxfordian and Svecokarelian orogenic cycles, and the Lewisian chronology for the Loch Maree region shows striking parallelism with the Precambrian chronology of NW. Europe.
Interpretation of geophysical observations between the Orkney and Shetland Islands
Authors: BOTT M. H. P. , BROWITT C. W. A.
Published: December 2007

A N.–S. orientated region of low gravity adjacent to the W. coast of the S. Shetland mainland is partly caused by a basin of probable Mesozoic age, as indicated by seismic refraction, sparker and bathymetric observations. The floor of the basin is estimated to be up to 2.3 km deep. The sediments of the western part of the basin are thin and of variable dip, but the eastern part takes the form of an eastward dipping sediment wedge or synclinal structure truncated on the east side by a normal boundary fault of contemporaneous or later age. The basin divides at its southern end into two tongues. The gravity low is also partly attributed to low density basement rocks such as granite, both at its north end and in the vicinity of Fair Isle, and to westward thickening of upper Palaeozoic (O.R.S.?) strata beneath the basin.

The postulated Mesozoic basin appears to be a subsidence structure along a major underlying dislocation approximately continuing the line of the Walls boundary fault. The new evidence is consistent with this being the Great Glen fault or a splay of it and interpretation of the linear magnetic gradient coinciding with the eastern tongue supports this hypothesis. The eastern boundary fault of the basin, however, appears to be normal. Tertiary transcurrent movement along the line appears to be improbable.
Lithostratigraphy and deposition of the type Portlandian
Authors: TOWNSON WILLIAM GEOFFREY
Published: December 2007

The “Portland Beds” of Dorset (Portlandian of English usage) are described in terms of a Group comprising two Formations and seven Members. Facies and thickness variations indicate the presence of a swell separating an East from a West Basin. The swell may be due to the movement of Triassic salt. The environmental history of the Portland Group is described in terms of three cycles consisting of major regressive and minor transgressive phases superimposed on an overall regression. The lower cycle consists of siliciclastics and dolomite deposited in a relatively deep marine environment. The dolomite formed by
in situ
replacement of lime mud. The middle cycle consists of cherty fine-grained limestones deposited on the outer part of a carbonate shelf. The abundance of replaced sponge spicules adequately accounts for the amount of chert. The upper cycle consists of cherty limestones passing up into shallow-water grainstones. Ooid shoals developed over the swell. These marine limestones are overlain by stromatolites and evaporites which formed on the basin margin.
The Minoan eruption of Santorini, Greece
Authors: BOND A. , SPARKS R. S. J.
Published: December 2007

The Minoan eruption of Santorini produced the following sequence of deposits: a plinian pumice fall deposit, interbedded surtseyan-type ash fall and base surge deposits, mud-flow deposits and ignimbrite interbedded with very coarse, well-sorted flood deposits. The variation of thickness and grain size in the plinian deposit indicates a vent 1 km west of Thera town. The base surges and surtseyan-type activity is interpreted as the result of sea water entering the magma chamber. The poorly sorted mud-flow deposits and ignimbrite are distinguished on their grain size, temperature and morphological characteristics, which indicate substantial rheo-logical contrasts in the mass flows which produced them. Grain size analyses show wide ranges in the lithic contents of the different types of deposit: ignimbrite (35–60%), mud-flows (20–30%) and the pyroclastic fall and base surge deposits (4–15%). The ignimbrite is enriched in crystals, complemented by depletion in fine air-fall ash beds that interstratify with the ignimbrite. The gas velocity of the plinian phase is estimated as 550 m/s, the eruption column height as greater than 20 km and it is shown that only particles of 2 mm could have reached Minoan Crete.
Levels of disagreement in the Sedgwick–Murchison controversy
Authors: RUDWICK M. J. S.
Published: December 2007

The controversy between Adam Sedgwick and Roderick Murchison about the meaning of the ‘Cambrian’ and ‘Silurian’ systems stemmed from differences on the technical (i.e. stratigraphical), methodological, theoretical and metaphysical levels. Their argumentative personalities merely accentuated their substantive disagreements.
A strain study of a granite–granite gneiss transition and accompanying schistosity formation in the Betic orogenic zone, SE. Spain
Authors: BORRADAILE GRAHAM J.
Published: December 2007

An allochthonous granite-bearing tectonic unit in the Alpine mountain belt of SE. Spain shows all transitions from meta-granites with original igneous textures to granite-gneisses with a single, regionally subhorizontal schistosity. Locally, the transition may be recognized in ‘shear zone’ type structures and this is suspected on a regional scale. In some out-crops of deformed meta-granite, large feld-spar phenocrysts show preferred orientation with maximum pole densities of (010) faces perpendicular to schistosity. The symmetrical arrangement of the poles with respect to the tectonic fabric elements, and increasing preferred orientation with schistosity development favour an absence of preferred orientation prior to deformation. The minimum strain responsible for the preferred orientation may be determined by progressively "undeforming" the orientations of the phenocrysts until the assumed, original random distribution is achieved. In this way strains in excess of +150% within the schistosity, and more than −77% normal to the schistosity have been found.

The large strains associated with a sub-horizontal schistosity could account for a considerable part of the displacements between flat-lying tectonic units of different competence. Furthermore, the large strain differences between different lithologies might account for the initiation of tectonic contacts and individualisation of nappes.
Mechanisms and dynamics of strombolian activity
Authors: BLACKBURN E. A. , WILSON L. , SPARKS R. S. J.
Published: December 2007

Strombolian explosions at Heimaey and Stromboli are described. Two main components of activity within a typical strombolian explosion are distinguished: an initial, high velocity, gas thrust part due to gas decompression and a subsequent convective part. Initial gas velocities at Heimaey averaged 157 m/s (standard deviation 28 m/s from 15 observations) and at Stromboli 31 m/s (standard deviation 12 m/s from 8 observations) for one vent and 56 m/s for a second vent. Velocities decreased approximately exponentially with height, and decelerations of up to 50 gravities were observed during the gas thrust events. A model of the gas thrust process is developed and values are deduced for the gas/solid mass ratio in the ejected material. Evidence is resented for the several-foId concentration of gas into that part f the magma expelled explosively, and a model in which large bursting gas bubbles are responsible for the explosions is shown to be compatible with the observations. Excess pressure within such bubbles is found to be of order 2.5 × 10
4
N/m (0.25 atmospheres) at Heimaey and 600N/m
2
(0.006 atmospheres) at Stromboli. Pressures inside bubbles of a few metres diameter are found to be of comparable magnitudes. Average gas release rates of 3 to 6 × 10
3
kgm/s at Heimaey and at least 0.13 kgm/s at Stromboli are indicated.
Preliminary geological interpretation of the Bristol Channel approaches
Authors: DORÉ ANTHONY G.
Published: December 2007

Interpretation of shallow seismic reflection profiles indicates a thick Permo-Triassic to Jurassic sequence, overlain in the west of the region by at least 400 m of upper Cretaceous. Both sequences are folded along E.–W., westerly-plunging axes. Cores obtained from an area 15–20 km NW. of Lundy have given ages ranging from Permo-Trias to ?upper Jurassic. Deposits of postulated Palaeogene occupy a shallow, partially faulted basin in the SW. of the region. The Tertiary NW.–SE. wrench fault system of Devon and Cornwall can be shown to extend into the area.
Deformation and metamorphism of Dalradian rocks and the evolution of the Connemara Cordillera
Authors: YARDLEY BRUCE W. D.
Published: December 2007

Dalradian metasediments in the Cur district of north-east Connemara have had a complex history of deformation and metamorphism. The earliest schistosity present formed during biotite-grade metamorphism and may be mimetic after a compaction fabric. Subsequently, the rocks attained garnet grade and major D
2
folds developed. This deformation involved an initial buckling followed by a coaxial homogeneous flattening and the structures produced were probably initially upright. After D
2
, staurolite, and locally kyanite, grew under moderately high pressure conditions. Continued increase in metamorphic grade was, however, apparently accompanied by regional uplift and erosion, for staurolite breakdown occurred at lower pressures than those required to form kyanite. Furthermore, the highest grade metamorphism was accompanied by a steepening of the thermal gradient, since breakdown of the assemblage staurolite + muscovite + quartz produced andalusite at high structural levels, but sillimanite deeper down. D
3
deformation began after the initial uplift at the peak of metamorphism and produced two major northward-facing nappes thrust over a basal fold-nappe. The nappes root to the south of the Corcogemore Mountains but continued uplift in south Connemara faulted out the root zones as later nappes developed. After cooling, broad open D
4
folds were formed and the Connemara Schists were thrust up and to the south over lower grade rocks. Uplift of the Connemara region may have been complementary to the subsidence of the Mayo Trough to the north, in which case the oldest Ordovician rocks in South Mayo may have been deposited at the same time that the peak of metamorphism was attained in Connemara.
Aspects of materials science of interest to tectonic studies
Authors: ATKINSON B. K.
Published: December 2007

Of The current research trends in tectonophysics, the study of deformation mechanisms and of relations quantifying their characteristic stress-strain-time behaviour (constitutive equations) should produce some of the most significant improvements in the interpretation of the structures and fabrics of deformed rocks. Such studies can shed light on phenomena as widely disparate in scale as the extent to which geologically significant flow occurs in the Earth's mantle, and the nature of preferred orientation in tectonites. They deal with phenomena that are of fundamental importance in attempts to model the structural evolution of the Earth's crust, either by computer studies or by scaled physical analogues of rock behaviour. In model studies the behaviour of real rock is assumed to follow a specific constitutive equation, i.e. a deformation mechanism is assumed. Yet many geologists are unfamiliar with the physics and chemistry of deformation processes, and even those researching these fields rarely have the time to take full advantage of the enormous quantities of pertinent literature produced by materials scientists.

Geologists and materials scientists both face similar problems in studying the phenomena of flow and fracture. Moreover, the increasing industrial concern with ceramics as new engineering materials means that scientists working in these two fields are interested in the deformation properties of often very similar materials. Meetings designed to promote an exchange of ideas can thus be of benefit to both disciplines. An important role of such meetings is to serve as the extent to which geologically significant flow occurs in the Earth's mantle,
Volcanic processes in ore genesis
Authors: GASS I. G.
Published: December 2007

Two major themes pervaded this joint meeting of the Volcanic Studies Group and the Institute of Mining and Metallurgy. On the one hand were the ‘academics’ who, using trace element and isotope geochemistry and even naked thermodynamics, erected hypotheses and models for the tectonic setting, origin and circulation of ore forming fluids. At the other extreme were those who provided the critical evidence as to whether these data applied to a particular ore deposit. Fortunately, speakers such as J. P. Hunt, T. Sato and G. Constantineou with experience in both areas more than adequately bridged the all-too-common gulf between the two.

Stable isotope studies strongly suggest that the origin of the ore-carrying solutions was either sea-water, in the case of the massive sulphides formed at or near constructive margins, or meteoric waters for ore bodies such as porphyry coppers, emplaced above subduction zones. The role of magmatic waters is minimal in the former and minor in the latter; magmatic processes seem to provide the thermal energy and very little else. Both thermodynamic models of geothermal systems (J. W. Elder), or modification of stable isotope ratios (E. T. G. Spooner & T. H. E. Heaton) indicate that the circulation of the solutions that cause mineralization follow immediately after the magmatic thermal event and that they are short-lived in terms of thousands rather than millions of years and vigorous. There are therefore signs of a semi-quantitative breakthrough in the understanding of geothermal processes. This has been brought about by the use of
Palaeogeographic significance of rocks and structures beneath the Vourinos ophiolite, Northern Greece
Authors: NAYLOR MICHAEL A. , HARLE TIMOTHY J.
Published: December 2007

The Vourinos ophiolite was thrust on to a SW-dipping sedimentary sequence comprising thick Triassic-Jurassic marbles (platform carbonates) overlain by the late Jurassic Ayios Nicolaos Complex. The sedimentary sequence was deformed and metamorphosed in early Cretaceous times, broadly contemporaneous with ophiolite emplacement. Two facies are identified in different thrust sheets of the Ayios Nicolaos Complex: siltstones and shales with fine tufts occur in the east, while in the west, coarse tufts, cherts and olistostromes are also present. The olistostromes may have developed during the initiation of a subduction zone at the western edge of the carbonate platform. The emplacement of the ophiolite was from the SW, as shown by a Hausen diagram. The oceanic source for the Vourinos ophiolite was probably the same as that for the Pindos and Othris ophiolites, and lay SW of the Pelagonian zone, rather than in the Vardar zone to the NE. It is suggested that the Ayios Nicolaos Complex is essentially a stratigraphic sequence, and not a tectonic mélange as previously described.
Remanent magnetism of middle Old Red Sandstone lacustrine and fluviatile sediments from the Orcadian basin, Scotland
Authors: TURNER P.
Published: December 2007

A palaeomagnetic survey has been made of fluviatile red beds and lacustrine flagstones in the Orcadian Basin. The results from five facies are all different in important respects and this suggests that the palaeomagnetic history is strongly influenced by short-term and long-term diagenetic processes. Red beds from below the Caithness Flagstones retain much of their original magnetization, probably due to the protection of quartz cementation. Red beds from above the Caithness Flagstones have stable magnetizations but they are apparently random in direction. This is because these porous sandstones were not protected by extensive cementation and had a long history of magnetization due to the continuous penetration of oxidizing agents.

The Caithness Flagstones had varied palaeomagnetic histories and demonstrate the importance of early diagenetic events. Siltstones and dolostones in the lower Caithness Flagstones are unstable due to the presence of normal and reversed components with similar blocking temperatures. The Achanarras Limestone, a carbonate laminite deposited under strongly reducing conditions, has a stable magnetization but this is of post-Palaeozoic age and there is no original magnetization preserved. Flagstones of the Spital Group in the upper Caithness Flagstones have stable magnetizations carried by authigenic pseudo single-domain (PSD) magnetite apparently produced during early diagenesis. Throughout the Caithness Flagstones both normal and reversed components are present in many individual specimens. This makes it extremely difficult to obtain palaeomagnetically ‘clean’ directions and casts doubt on the use of the Caithness Flagstones for precise palaeomagnetic work.
A geological interpretation of the aeromagnetic map of east-central Shetland
Authors: FLINN DEREK
Published: December 2007

Exposure is very unevenly distributed within the area of the Institute of Geological Sciences Sheet 128 as there are large areas of peat and sea. However, the aeromagnetic map shows a complex pattern of anomalies covering the whole area. Ground traverses with a magnetometer show that most of the positive anomalies are caused by rocks which crop out but are very poorly exposed. The outcrops were delineated with the aid of magnetometer traversing. The occasional exposures reveal that the rocks causing these anomalies are magnetite-rich schists of pelitic and greenschist types and serpentines. Ground traversing with a magnetometer shows that the magnetic schists form narrow bands which act as marker horizons in poorly exposed areas. The pattern of aeroanomalies caused by the magnetic schists and the non-magnetic rocks with which they alternate continues over the sea and enables predictions to be made about the geology of the sea areas.
Oxygen and hydrogen isotope relations in the Berridale batholith
Authors: O’ NEIL J. R. , CHAPPELL B. W.
Published: December 2007

Two contrasting types of Palaeozoic granitoids are of widespread occurrence in SE Australia and can generally be distinguished by their chemistry, mineralogy, field relations and initial strontium isotope ratios. Chappell &
White (1974)
have proposed that the granitoids are derived by partial melting of two different types of source materials: (1) igneous or ‘I-type,’ and (2) sedimentary or ‘S-type.’

Oxygen and hydrogen isotope compositions were measured on 63 whole-rock samples of both fresh and altered granitoids and xenoliths. Analyses were also made of representative mineral separates from these rocks. For ‘S-type’ plutons, average δ
18
O values range from 9.9 to10.5, whereas for the ‘I-types’ the range is 7.9 to 9.4 Xenoliths are about 1 per mil depleted in
18
O and generally enriched in D relative to the hose rocks. The average δD values (and water contents) are –62 ± 4 (1.10%) and –77 ± 12 (0.73%) for ‘S’ and ‘I’ granitoids, respectively. Individual δD values range from –50 to –102 and correlate well with water contents: the more water-rich the granitoid the greater the deuterium content. Per mil
18
O fractionations between quartz and biotite are rather large ranging from 5.0 to 6.9 (independent of granitoid type), with a mean of 6.0. Thus typical isotope temperatures of about 520°C are inferred and retrograde effects are indicated.
Sulphur isotopes in petrology
Authors: COLEMAN M. L.
Published: December 2007

Variation in sulphur isotope ratios is caused by equilibrium fractionation and kinetic fractionation. Two groups of samples show a narrow range of
34
S/
32
S: sulphur from sea-water sulphate, and from meteorites and basic rocks; the former show an enrichment, δ
34
S, +20%
0
with respect to the latter. They are identifiable source materials from which the complete range of values is derived by fractionation processes. Experimental and theoretical work shows the magnitude of these effects and allows interpretation of data from natural samples in terms of isotopic temperatures or source of the sulphur or both. Data mainly from rocks not associated with ore deposits is reviewed. The wide range of values in sediments can be attributed to bacterial reduction of sea-water sulphate under various conditions. Basalts give ratios near to the meteorite value, 0%
0
, and in detail relate to the conditions of petrogenesis. Some granites are enriched up to +30%
0
, probably from late-stage differentiation, but samples from the SE Autralian, New England batholith have ratios which fall into two groups: those within a small range from −3.6 to +5.0%
0
and those which are generally higher or lower than that range. These respectively relate to an igneous or sedimentary source for the rocks as distinguished by other geological criteria.
The evolution of the Pan African crystalline basement in NE Africa and Arabia
Authors: GASS I. G.
Published: December 2007

The crystalline basement of NE Africa and Arabia has all the geophysical and geological characteristics of continental crust. But, field and petrographic evidence indicate an intraoceanic island arc environment for the mainly volcanoclastic sediments and geochemical data suggest that magmatic products were generated at or above easterly inclined Benioff zones. Some of the mafic-ultramafic masses that lie in NE zones across the region have been identified as ophiolites and the zones are thought to mark the approximate margin of individual arc systems; four or five arc systems are identified. The episodic evolution of these Proterozoic island arcs took
c.
600 Ma (1100–500 Ma) before the continental character of the area was attained. As calc-alkaline igneous rocks and intervening ophiolite bodies occur elsewhere in northern Africa, the Pan African island arc model may have wider application.