bluuebunny/crossref_metadata_2025 huggingface dataset:
THE STRATIGRAPHY AND STRUCTURE OF THE ERRIGAL AREA, COUNTY DONEGAL, IRELAND
Authors: RICKARD MICHAEL JOHN
Published: October 2009

The Dalradian rocks of the Errigal area form part of the envelope of the Donegal granites. The sedimentary succession established in the adjacent Creeslough district by McCall (1955) is traced to the south-west, where eleven stratigraphical divisions, consisting of quartzites, banded quartzites, pelites, and limestones, amount to a thickness of at least 14,000 feet.

The major structure in the area is a recumbent syncline; extensive sliding along the normal limb of this fold has removed up to 6000 feet of strata. The axial trend is variable, and bending has caused subsidiary cross-folding and shearing. Accompanying the emplacement of granite bodies, minor structures and thermal metamorphism were superimposed on the regional fabric developed during the major folding. A detailed picture of the behaviour of these various structures is provided by an analysis of the minor elements.
CHARNOCKITES AND THEIR ASSOCIATED GNEISSES IN THE PRE-CAMBRIAN OF CEYLON
Authors: COORAY PERCIVAL GERALD
Published: October 2009

The Pre-Cambrian rocks of Ceylon are divided into the granulite-facies Highland Series (metasediments and charnockites) and the almandine-amphibolite facies Vijayan Series (granites, granitic gneisses, and migmatites). The Vijayan Series represents, in part, Highland Series rocks which were further altered during a later metamorphic episode or episodes. At the junction of the two series is a transitional zone which possesses lithological, structural, and metamorphic features characteristic of each. Charnockites are abundant in the Highland Series and rare in the Vijayan, and charnockitic biotite-gneisses are widely developed in the transitional zones.

The field-relations, structures, tectonics, lithology, and grades of metamorphism of the major Pre-Cambrian units are described and the relations of these units to each other are discussed. It is shown that in the course of retrogressive metamorphism (probably in the presence of water) that converted Highland Series rocks to Vijayan types the charnockites were first altered to charnockitic biotite-gneisses and ultimately to non-charnockitic biotite- and hornblende-bearing rocks.
TERTIARY WELDED TUFFS IN EASTERN ICELAND
Authors: WALKER GEORGE PATRICK LEONARD
Published: October 2009

The welded acid tuffs that are a minor constituent of the volcanic pile are hard felsitic rocks, usually highly vesicular, with a basal glassy layer. They usually have the characteristic microtexture of welded tuffs, but field criteria are more reliable in distinguishing them from lavas and non-welded tuffs. An isopach map is given of the Skessa tuff, which is the product of a single subaerial eruption. The original extent of the welded parts of this tuff is estimated to have been 100 square miles, and its average thickness 25 to 30 feet ; peripheral outcrops are not welded, and cover an additional 70 square miles. In the welded parts the tuff particles were deformed, roughly aligned, and welded together under their own weight and momentum and the accumulated tuff remained plastic long enough for vesicles to form.

A classification of tuff deposits into five grades is proposed which is based on the plasticity and temperature of the tuff particles. The Skessa tuff is a representative of the rather rare grade in which the particles had the highest plasticity and, presumably, temperature. Bubbles of basaltic glass that occur in the tuff appear to indicate simultaneous eruption of acid and basic magma.
THE GEOLOGY OF THE AREA AROUND LEINTWARDINE, HEREFORDSHIRE
Authors: WHITAKER JOHN HARRY MCDONALD
Published: October 2009

Wenlockian, Ludlovian, and lowest Downtonian strata have been mapped over an area of about ten square miles east of Leintwardine, where the structure is an asymmetrical syncline plunging east-north-east. The southern limb dips northward at about 35°, the northern limb eastward at about 8°.

Wenlock Shale and Wenlock Limestone (together 1560 feet thick) are succeeded by up to 1900 feet of Ludlovian rocks, divided into Elton, Bringewood, Leintwardine, and Whitcliffe Beds (Holland, Lawson &
Walmsley 1959
). Where complete, the succession is similar to that at Ludlow, but is thicker and less calcareous and with more evidence of instability (crinkle-marks and slump-structures) reflecting deposition nearer to the edge of the shelf. Basin elements in the fauna support this view of the palaeogeography. The lowest Downtonian strata (140 feet mapped) compare closely with those of neighbouring areas.

There is one major break in the sequence, within the Lower Leintwardine Beds ; six parallel channels, trending and deepening towards the west-southwest (i.e. from shelf to basin), are interpreted as Ludlovian submarine canyon-heads and show many features in common with their modern counterparts. Later these tended to fill up, with occasional ‘flushing out’, until they were eliminated by Upper Leintwardine and later sedimentation.
DISTRIBUTION OF MIOSPORES THROUGH COALS AND SHALES OF THE COAL MEASURES SEQUENCE EXPOSED IN WERNDDU CLAYPIT, CAERPHILLY (SOUTH WALES)
Authors: SULLIVAN HERBERT JAMES
Published: October 2009

Spore assemblages are described from coals and shales collected at 45 horizons within the Coal Measures sequence exposed at Wernddu claypit, near Caerphilly, South Wales. The changes in the composition of the microfloras of Westphalian shales are related to those known to occur in assemblages isolated from coals. Particular attention has been paid to the vertical ranges of the spores, and 35 species are recognized as of special stratigraphical value. Comparisons are made with the spore distributions in neighbouring parts of South Wales and other British coalfields. Recent accounts of the microfloras from Northern Hemisphere continents are briefly reviewed.
THE GEOLOGY OF THE FAROES
Authors: NOE-NYGAARD ARNE
Published: October 2009

Geological mapping of the Faroe Islands has revealed a sequence of nearly 3000 metres of lavas. The lavas fall into three main divisions. There is also a thin series of sediments.

(1) A
lower lava series,
about 900 metres thick, consisting of forty to fifty flows, with an average thickness of about 20 metres, intercalated with thin beds of tuffs. Single flows can be traced for long distances. The rock-types are monotonous. Columnar jointing occurs throughout the series, but is most pronounced near the top.

(2) After an erosional interval, a
sedimentary series,
whose main members are clays containing a workable coal-seam, was deposited; its average thickness is 10 metres. These beds form the only continuous strata in the islands.

(3) The sedimentary period was brought to an end by explosive volcanism, producing agglomerates and tuffs which reach a thickness of more than 100 metres. Thin lava-flows are intercalated in the upper part of this series, which passes upwards into the
middle lava series,
well over 1350 metres thick, made up of thin flows of many different rock-types, all of which are developed as ropy lavas with reddish surfaces. The lavas are rich in amygdales filled with zeolites; ordinary tuffs are practically absent. This series was probably deposited rapidly and with few interruptions. Many vents, now filled with agglomeratic material, have been recorded.

(4) Finally, the
upper lava series,
625 metres thick, was erupted. It consists of well-marked lava-flows intercalated with tuffs, and its appearance is comparable with that of the lower series, although the individual lava-flows are only half as thick. The upper lavas are composed of several different rock-types; some show a tendency towards columnar jointing. Pale-coloured lavas with feldspar phenocrysts are dominant in the west, whereas fine-grained dark olivine-basalts with few or no phenocrysts are dominant at the same level in the east.

After surface volcanism had ceased, irregular intrusions were injected into the sediments and the overlying agglomerates, and sills were intruded between the middle and upper lava series. The plateau is cut by several hundred dykes, most of which are concentrated in a belt that trends E.-W. across the northern group of islands.

After the epoch of volcanic activity the region was weakly folded, forming a gentle anticline, the axis of which coincides with the present-day watershed. The numerous master-joints, which form two sets, are connected with this structure. The action of running water on these master-joints has produced the rectilinear
geo8
(Faeroese
Gjógver).
THE STRUCTURE OF THE NORTH-EASTERN TRACT OF THE DARTMOOR GRANITE
Authors: BLYTH FRANCIS GEORGE HENRY
Published: October 2009

The granite margin from Sticklepath to Bridford, of which the only map hitherto available has been the one-inch Old Series sheet 25 dating from 1866, has been re-mapped, together with the rest of the area lying north-east of the Lustleigh-Sticklepath fault-system (
Blyth 1957
). Complex faulting in the Lustleigh area is described.

The fracture-pattern consists of a late NW.-SE. fault-system with associated NNW.-SSE. faults, which is superimposed on an earlier series of fractures including joints, aplites, and tourmaline and haematite veins.

The northern part of the Dartmoor granite is visualized as a thick intrusive sheet with an outwardly dipping contact against Lower Culm sediments. More than one episode of movement on the NW.-SE. and NNW.-SSE. faults is postulated, and some part of it is thought to be of Tertiary age. This has resulted in an area of broken granite which has been more readily eroded than the area to the south-west of the faults.
Devonian ammonoid successions and facies in Devon and Cornwall
Authors: HOUSE MICHAEL ROBERT
Published: October 2009

The ammonoid successions in the Devonian rocks of the Torquay, Chudleigh, and Padstow areas of Devon and Cornwall are described and it is shown that representatives of all the German Devonian ammonoid
Stufen
occur in south-west England. The ammonoid successions demonstrate significant facies changes within the Middle and Upper Devonian among the areas discussed.

In the Torquay area the zone of
Anarcestes lateseptatus
is recognizable in the
Calceola
Shales, and in the massive Givetian limestones two ammonoid faunas occur, a lower zone with
Maenioceras molarium
and an upper zone with
M. terebratum.
The main Lummaton Shell Bed includes the fauna of the
terebratum
Zone. Limestone sedimentation probably continued into the Lower Frasnian, but the
Manticoceras cordatum
and
Crickites holzapfeli
zones are represented at Saltern Cove by thick argillaceous developments: it appears that at Torquay these zones may be reduced in thickness. An ostracodslate facies follows immediately above the
holzapfeli
Zone; ostracod evidence shows that this facies continues into the Upper Famennian.

A similar Middle Devonian succession, but without ammonoids, is developed at Chudleigh, but the Upper Devonian sequence is a reduced one of nodular limestones and slates with nodules in which the
Manticoceras, Cheiloceras, Platyclymenia, Clymenia,
and
Wocklumeria Stufen
occur. The name
Mount Pleasant Series
is proposed for the Famennian sequence, which is 170 ft in thickness. This Upper Devonian facies is thought to be comparable with the German
schwellen
facies in contradistinction to that at Torquay, which is of
becken
type.

The Middle Devonian in the Padstow area is predominantly of slate facies with minor calcareous developments in the Eifelian and Givetian. Three main goniatite faunas can be recognized within the Middle Devonian. Good goniatite faunas of the Frasnian
cordatum
Zone occur in banded slate facies and these are overlain by a thick series of ostracod-bearing slates. It is evident that the ostracod facies enters at a lower level than at Torquay.

The following new species of goniatites are described:
Archoceras ussheri, Ponticeras pedderi,
and
Protornoceras foxi.
The Breiddalur central volcano, eastern Iceland
Authors: WALKER GEORGE PATRICK LEONARD
Published: October 2009

The Tertiary central volcano of Breiddalur, the first to be described of several—perhaps many—such volcanoes in Iceland, has a volume of about 100 cubic miles of basic, intermediate, and acid lavas and pyroclastic rocks, with a maximum thickness of 5000 to 6000 ft. The basic lavas are unusually thin owing to the fact that they were erupted on a sloping surface. The central volcanicity contrasts with the flood-basalt fissure-eruptions of the surrounding country; at times the volcano stood up as a co ne above the flood-basalt plains, but flood-basalts were all the time being erupted; they were interdigitated with the products of the volcano (so strikingly that the term ‘cedar-tree volcano’ seems appropriate), and later completely buried it.

The core of the volcano is marked by a profusion of acid lavas, pyroclastic rocks, and minor intrusions; in it the rocks are drastically altered and show variable and sometimes abnormally high dips indicative of cauldron-sub- sidence. A swarm of dykes locally constituting as much as 20 per cent of the country passes through the core.

The rocks above the core probably in part occupy a crater or caldera; they include agglomerate containing blocks of granophyre, granite, and gabbro from inferred syngenetic intrusions below the volcano; a palagonite-tuff and breccia with basalt pillows, probably form- ed in a crater lake; two welded acid tufts; and a thick rhyolite flow joined to its plug-feeder.

Acid rocks are mostly concentrated in or near the core, except for a spectacular group of parasitic rhyolites in which all stages in uncovering of the plug-feeders by erosion are seen. Simultaneous eruption of basic and acid magma from the same orifice is evidenced by one rock, which represents an emulsion of the two magmas, and also by a composite lava, with basic and acid components, which was erupted from a composite dyke.
Lunar tectonics
Authors: FIELDER GILBERT
Published: October 2009

The lunar lineaments are described and their origin is considered.

The components of the lunar grid-system—a system of intersecting lineaments comprised of elongated ridges, joints, crater-chains, and rilles—are described, and methods for producing orthographic charts of the principal global families A, B, C, and D of the grid-system are given. Each family, or system, of lineaments has a well-defined strike and is distinguished from one major regional system of joints (system R
1
) which is associated with Mare Imbrium The global systems display a strong symmetry about the Moon’s central meridian.

Discussion of the origin of system R
1
and a similar regional system of joints associated with Mare Humorum leads to the conclusion that these maria are igneous sinks and were not produced by impact. Examples of dip-slip and strike-slip faults are given.

General properties of the mutally orthogonal systems A and B are listed and interpreted in terms of a general meridional pressure in the Moon’s crust.
The crystallization of feldspar in volcanic acid liquids
Authors: CARMICHAEL IAN STUART EDWARD
Published: October 2009

The paths of feldspar crystallization in volcanic acid liquids can be illustrated by the relationship of feldspar phenocrysts to groundmass feldspar in porphyritic pitchstones and rhyolites. In this way, a concept of the undetermined system CaAl
2
Si
2
O
8
-NaAlSi
3
O
8
-KAlSi
3
O
8
-SiO
2
can be obtained. In this account the various sub-solidus transformations of alkali feldspar and plagioclase are neglected, the emphasis being rather on feldspar-liquid equilibria. It is shown that the equilibrium crystallization of acid liquids similar in composition to the Icelandic rhyolites is characterized by a single feldspar, namely a representative of the plagioclase-anorthoclase solid-solution series. In the more potassic acid liquids of the British Tertiary and the San Juan region, Colorado, phenocrysts of alkali feldspar (sanidine) and plagioclase are commonly found, plagioclase being subsequently resorbed under certain conditions during equilibrium crystallization.

The paths of well-described tholeiitic and alkaline volcanic series in the tetrahedron CaAl
2
Si
2
O
8
-NaAlSi
3
O
8
-KAlSi
3
O
8
-SiO
2
indicate that under conditions of fractionation the later salic liquids may not become sufficiently enriched in potassium for two feldspars to crystallize; instead, a representative of the plagioclase-anorthoclase series appears. In the orogenic volcanic series, where modification of basaltic magma by assimilation is believed by many to play a dominant role in the production of andesite, the associated acid liquids typically give rise to two-feldspar assemblages. It is therefore suggested that in areas where intermediate rocks are largely absent, two-feldspar rhyolites may result directly from fusion, a conclusion not at variance with the available evidence from the British Tertiary province.
Tilloids in the West Congo geosyncline
Authors: SCHERMERHORN LODEWIJK JACOB GERARD , STANTON WILLIAM IREDALE
Published: October 2009

In the West Congo geosyncline, which stretches from Gaboon far into Angola, the Lower and Upper Tilloid Formations extend continuously over more than 100 000 square kilometres. Of Late Pre-Cambrian age, they are most probably equivalent to the
Grand
and
Petit Conglomérats
of Katanga. They have generally been thought to consist of tillites and periglacial beds, but detailed study in north-west Angola has led to their reinterpretation as submarine mudflow deposits.

The tilloid formations are generally well-bedded sequences consisting of tilloids (till-like pebbly mudstones and greywackes), conglomerates, greywackes, mudstones, quartzites, and limestones, with transitional rock-types. The tilloid clasts comprise angular to rounded intrabasinal fragments eroded from preceding strata, well-rounded extrabasinal crystalline stones, and (in the Lower Tilloid Formation only) debris from intraformational spilite lavas. Graded bedding occurs, sometimes in the tilloids and frequently in the quartzites and greywackes.

Each formation marks the beginning of a sedimentary cycle within the West Congo geosyncline major cycle, and was laid down in a sharply subsiding basin after emergence and slight erosion of the preceding beds. Each is followed by rhythmically bedded turbidite formations. Tilloids at other levels in the West Congo System are also described.

In each formation marine sediments are intercalated among tilloids, ruling out the possibility of a continental origin. Lithological, stratigraphical, and other evidence is over-whelmingly against a glacio-marine origin.

It is suggested that the tilloids were deposited from mudflows formed by the slumping of unconsolidated sediment on the shelf, incorporating mud, sand, gravel, and stones up to large boulder size. This material, of both intrabasinal and extrabasinal provenance, was thoroughly mixed as it flowed far into the geosyncline to be redeposited as tilloid. It is proposed to distinguish ‘flow tilloids’ of this kind from ‘slide tilloids’, less well mixed and smaller in size, formed by less mobile submarine slides. It is thought that they reflect a special tectonic environment of deposition (abrupt subsidence of the geosyncline with only slight elevation of the adjacent land areas) which gave rise to unusually dense turbid flows; tilloid deposition is thus seen as a special type of geosynclinal turbidite sedimentation.

Flow-tilloid formations appear to be characteristic of Late Pre-Cambrian geosynclines. The acceptance of a non-glacial origin for the West Congo tilloids would necessitate the re-examination of the evidence for a Late Pre-Cambrian glaciation.
The Lewisian complex of South Harris With some observations on the metamorphosed basic intrusions of the Outer Hebrides, Scotland
Authors: DEARNLEY RAYMOND
Published: October 2009

The metamorphic petrology and history of the Lewisian rocks of South Harris are described.

The paragneisses in each of the two main belts are divided into three lithological and possibly stratigraphical units, the disposition of which indicates folding in tight plunging isoclines along
Nw–Se
(Early Laxfordian) axes. Relic textures indicating an early (pre-Lax-fordian) metamorphism and folding are recognizable in the paragneisses and also in the pyroxene-granulites which appear to intrude the paragneisses. This early metamorphism is probably Scourian in age. The pyroxene-granulites are earlier than and are not comagmatic with the igneous complex.

The igneous complex, which is a metamorphosed differentiated (and possibly originally layered) anorthosite–gabbro–tonalite mass, together with the metamorphosed basic intrusions in its immediate vicinity and the widespread metamorphosed basic dykes and sills in the Outer Hebrides, constitute an essentially non-orogenic suite of post-Scourian pre-Early Laxfordian age. The geochemistry of this suite shows it to be tholeiitic in character and probably closely related to the Scourie dykes of the Scottish mainland.

Early Laxfordian granulite-facies metamorphism associated with the main
Nw–Se
folding of the area followed the emplacement of the non-orogenic igneous suite. A south-easterly plunge and north-easterly overturning characterize the folds to the north-east of the igneous complex; to the south-west the plunge is north-west, and the overturning is to the south-west.

A Late Laxfordian injection-complex situated to the north-east comprises extensive areas of migmatization and granitic intrusion and is associated with a front of hydrous retrograde metamorphism which strongly affects the Langavat paragneisses and parts of the igneouscomplex. The sinuous trend of the Langavat paragneisses is attributed to cross-folding of thisdate.

All the earlier rock-types are cut by a suite of Late Laxfordian granite pegmatites containing uranium, thorium, and rare-earth minerals.
Tertiary vents in the northern part of the Antrim plateau, Ireland
Authors: PATTERSON EDWARD MERVYN
Published: October 2009

Intrusive volcanic agglomerates at twenty separate localities along the northern coasts of County Antrim and County Londonderry are described. The agglomerates intrude the Upper Chalk and the immediately overlying Tertiary basalt lavas. Apart from doubtful instances at Downhill, in the extreme west of the area, the lavas cut by the vent-agglomerates belong to the Lower Lava Series of the Antrim plateau. In six instances the agglomerates can be seen to be closely associated with tuffs, interbedded with the lava-flows.
The succession and structure east of the Glaslyn River, North Wales
Authors: BEAVON ROY VERNON
Published: October 2009

The succession and structure of some mid-Ordovician sedimentary and volcanic rocks are described. Marine slates and grits are succeeded by welded and bedded rhyolitic pyroclastic rocks which are overlain by basic tuffs, lavas, and intercalated slates. A local intravolcanic unconformity cuts out over 5000 ft of strata below part of the Snowdon Volcanic Series. The fragmented debris of the missing strata forms a mixed deposit of breccias which overlies the unconformity in places. Normal faulting of Lower Caradoc age is postulated, and it is suggested that the unconformity is part of a buried volcanic collapse-structure. Timerelations suggest that the collapse was initiated by concealed intrusive activity near Aberglaslyn. The intrusion produced local thermal metamorphism and tourmalinization of the early Caradoc sediments in post-Harnagian and pre-Longvillian times.

The main structure is the south-westward continuation of the Dolwyddelan syncline, flanked to the west by a complementary anticline.
DISCUSSION OF PAPERS PUBLISHED IN PREVIOUS PARTS OF THE
QUARTERLY JOURNAL
Authors: Whitaker J. H. McD.
Published: October 2009

From Dr D. G. Stephenson:

This paper throws a new light on the environment of some of the early echinoids. It has been usual to consider these as inhabitants of lagoons or similar areas of shallow, still water, as Hawkins deduced for Palaeodiscus and
Echinocystis
from Church Hill. But Mr Whitaker's work has shown that
Palaeodiscus
and
Echinocystis
were preserved in sediments formed under the deepest water in the area. If they lived only in the submarine canyon-heads, their distribution was similar to that of the modern flexible echinoids, the Echinothurids, which Mortensen and others claim as descendants of these Palaeozoic forms.

But Hawkins considered that the preservation as complete specimens of these echinoids was due to rapid burial by a sudden influx of sediment. A similar explanation might hold for all the unusual fauna found in the channels. Flexible echinoids, asteroids, and the various arthropods all have skeletons made up of discrete units which might be dispersed on the death of their owners unless rapidly buried; the preservation of annelids is an unusual event for which explanations of this type are necessary. It seems possible that this fauna lived throughout the area, but that conditions were suitable for its preservation within the submarine canyon-heads only. It would be interesting to know if it were possible to distinguish between this alternative and the existence of a fauna living only in the channels. This makes no difference to the stratigraphy, but the palaeoecological implications are quite different.

The A
uthor’s
reply:

The
Continental drift
Authors: BULLARD EDWARD CRISP
Published: October 2009

During the nineteen-twenties and thirties there was a vigorous controversy as to whether the continents have moved. The arguments largely concerned similarities between now-separated continents. These similarities did not provide direct evidence of motion. There is now direct evidence for motion of hundreds of kilometres and perhaps of over 1000 km on transcurrent faults. Palaeomagnetism also has provided strong evidence for movement, the only alternative being to suppose that before the Eocene the Earth's magnetic field was nothing like a dipole and was not related to the axis of rotation. Recent work on the oceans makes it difficult to believe in 'land bridges' or 'lost continents'. The only plausible mechanism for moving the continents is thermal convection in the mantle with rising currents beneath the oceans. This leads to the suggestion that the oceans may be widening by tension cracks along the crests of the mid-oceanic ridges.
Metamorphism of the Ben More-Am Binnein area, western Perthshire, Scotland
Authors: JONES KENNETH ARTHUR
Published: October 2009

Several published studies suggest that a large part of the south-west Highlands, of which the area described forms a small part, represents an inverted stratigraphic succession (e.g.
Bailey 1922
;
Shackleton 1958
), and that the garnet isograd in the area is inverted (
Tilley 1925
; Elles & Tilley 1930). The present study was undertaken in order to determine, as far as possible, the structural and crystallization history of these rocks.

Three deformation phases have been recognized: the first resulted in the development of folds with north–south axes and axial planes lying statistically parallel to the regional foliation-surfaces; the second formed folds having axes with a 120° azimuth and axial planes dipping to the north-east; the third formed more open folds with Caledonoid (60°) axes. It is concluded that if large-scale regional inversion has occurred the rocks have possibly been overturned before the earliest distinguishable deformation phase. Microfabric study shows that recrystallization accompanied the three deformation phases. An intense and complex series of crystal growths, including growth of biotite, garnet, and albite, and regional diaphthoresis, occurred after development of the third-phase structures. This post-tectonic recrystallization formed the most common microfabric of the area, partly or totally obliterating earlier microfabrics; it is characterized by a low degree of preferred orientation of quartz
c
-axes.

Detailed examination of the garnet isograd leads to the conclusion that there is no evidence of its inversion in this area.
The stratigraphy and structure of the Silurian (Wenlock) rocks south-east of Hawick, Roxburghshire, Scotland
Authors: WARREN PETER TOLMAN
Published: October 2009

Re-mapping for the first time since 1899 has led to a re-interpretation of the succession and structure previously advocated for the Hawick area (Peach & Home 1899). Palaeontological and lithological evidence and ‘way-up’ criteria provide the basis for a completely revised stratigraphy proposed for the Wenlock rocks. Two facies are present, those of the Hawick and Riccarton Groups, each of which constitutes over 12 000 ft of strata. Four new stratigraphical divisions are erected in the Riccarton Group: the Stobs Castle, Shankend, Penchrise Burn, and Caddroun Burn Beds; and the Wenlock graptolite zones of
Cyrtograptus murchisoni, Monograptus riccartonensis, C. symmetricus,
and
C. lundgreni
are recognized. The graptolite faunas bear close similarities to the Wenlock assemblages of Bohemia, a feature most noticeable among the cyrtograptids, where the dominant basal Wenlock forms are
C. insectus
and
C. centrifugus.

Structurally, the area comprises five main units, each of which consists of one or more north-facing asymmetrical folds of Caledonoid trend. The units are separated by major high-angle faults, which are mainly reverse faults. Minor faults, especially wrench-faults, are important.
The Leannan fault
Authors: PITCHER WALLACE SPENCER , ELWELL ROYSTON WILLIAM DUNLOP , TOZER CHARLES FALLOWS , CAMBRAY FRANK WILLIAM
Published: October 2009

A powerful north-east-trending fault cuts right across the north-west corner of Ireland and forms the most important member of a system of steep wrench-faults that dissect the Dalradian rocks of Donegal into parallel strips.

The contrast between the rocks flanking this Leannan fault is very marked. On the north-western side the outcrops of the same succession of metasediments run parallel to the fault-line for over 60 miles; over this distance they show little change in lithology, structure, or metamorphism. On the other side the geology varies considerably along the fault, and, except in the north-east, the outcrops run at a high angle to the fault-line; as a result, several different rock-groups are brought against the fault. The metamorphism increases progressively to the south-west so that rocks of kyanite grade are finally brought against others of chlorite grade.

The main movements on the fault are shown to have occurred between the deposition of red beds, presumably of Lower Old Red Sandstone age, and the deposition of Viséan marine sediments.

The fault-zone generally consists of one main break accompanied by two others of lesser importance: together these fractures isolate narrow strips of metasediments in which inverted sequences are the rule. It is argued that the inversion of these strata predates the faulting, and that they were derived from the now eroded limb of a great recumbent fold. Along the main fault a total of 60 yards of intense deformation is usual, and black schist, platy siliceous mylonites, and quartzitic breccias are the result; the steep platiness is always set at an acute angle to the fault. Two separate movements are shown to have occurred; a downthrow to the south-east amounting to several thousand feet is combined with a left-handed displacement, the amount of which, though difficult to estimate, may be as much as 25 miles.

The Leannan fault is directly in line with the Great Glen fault and the possibility that it is a continuation of this structure is discussed.
Gravity measurements in the north-eastern part of the Irish Sea
Authors: BOTT MARTIN HAROLD PHILLIPS
Published: October 2009

During the summer of 1961 124 new gravity measurements were made in the north (mainly north-east) Irish Sea with an underwater gravity meter.

In north-west England, south-west Scotland, and Northern Ireland a regional rise in the Bouguer anomaly is observed on approaching the north Irish Sea; a high regional Bouguer anomaly of more than 40mgal is also characteristic of the Isle of Man. The author considers that this reflects either a crustal thinning of about 3 km or a denser crust (by about0 03g/cm
3
) beneath the Irish Sea; denser basement rocks may in part be responsible.

Over most of the sea area surveyed negative gravity anomalies of 20mgal to 40mgal amplitude are superimposed on the high regional Bouguer anomaly. Both the shape of the anomalies and their correlation with the surrounding coastal geology suggest that they are essentially caused by large sedimentary basins. The two main negative anomalies thus interpreted are (
a
) between the Point of Ayr, the Solway Firth, and Wigtown Bay (thought to be at least 2130 m [7000ft] deep), and
(b)
between south Cumberland and the Isle of Man (probably at least 2440m [8000ft] deep). Coastal geology suggests that Carboniferous and New Red Sandstone rocks form the major 'fill', although sediments of Old Red Sandstone or post-Triassic age cannot be ruled out.

A negative anomaly of nearly 20mgal amplitude forms the south-eastern continuation into Luce Bay of the negative anomaly over the Stranraer New Red Sandstone basin. It closes to the south-east near the mouth of Luce Bay. As on land, it is interpreted as an asymmetrical basin of New Red Sandstone and earlier sedimentary infill with a steep (? faulted) northeastern margin, reaching a maximum depth of at least 1340 m (4400 ft).

A single gravity traverse westwards from Peel reveals a sharp gravity drop of about 15mgal immediately off shore; this is interpreted as a sedimentary basin lying off the west coast of the Isle of Man. The Isle of Man thus appears to be an uplifted horst-like region of Lower Palaeozoic rocks with the northwestern and south-eastern coastlines controlled by the margins of steep-sided sedimentary basins of post-Lower Palaeozoic age.
The uses and limitations of beta-diagrams and pi-diagrams in the geometrical analysis of folds
Authors: RAMSAY JOHN GRAHAM
Published: October 2009

The two standard procedures for determining the directions of fold-axes from measurements of the orientation of planar surfaces in the fold are examined to determine the validity of the conclusions that are generally based on them. With some types of folds, an analysis of the data using a
β
-diagram gives results that are particularly difficult to interpret with precision. Great errors in the position of the significant
β
-intersections may be expected under certain circumstances, and geologically meaningless
β
-points may also be abundant. Where the folding is inhomogeneous,
β
-diagrams generally produce a particularly high proportion of spurious
β
-points, often greatly outnumbering the significant
β
-points. Under these circumstances
β
-diagrams are unreliable and may give a false impression of the structural geometry. The most satisfactory method of analysing field data is by using π-diagrams. Although there may be difficulties in their interpretation when used with certain types of fold, modifications of the method can be employed to determine accurately the axes of both very open and near-isoclinal folds. If π-diagrams are prepared from data collected in regions of inhomogeneous folding the inhomogeneities are often immediately apparent, making it possible to subdivide the region into smaller areas of greater homogeneity. No mass of spurious points will be produced in such circumstances as would be found in a
β
-diagram prepared from the same data.
Lower Palaeozoic plankton
Authors: BULMAN OLIVER MEREDITH BOONE
Published: October 2009

The graptolite biocoenosis is accepted as the epipelagic or oceanic plankton fauna of the Lower Palaeozoic, although the geosynclinal deposits in which graptolite remains occur are not typically oceanic. Local variation within geosynclines implies a measure of permanence and stability in their faunas, but the general similarity in graptolite successions calls for frequent intercommunication, and epipelagic plankton probably drifted into geosynclinal seas from outlying oceanic areas. The location of these oceans introduces the problem of continental drift.

Reconsideration of morphological evidence suggests that nema (or virgula) attachment was the exception in the adult graptoloid but may have been more prevalent in juvenile stages; the occurrence of a general ‘size limit’ for stages with prominently developed nema could prove functionally significant. Some form of vacuolated extrathecal tissue seems the most plausible alternative buoyancy mechanism for adult forms. There is some evidence of attachment in (adult) Tremadocian dendroids, and the origin of the Graptoloidea may be causally related to a phase in the development of Sargasso-like seas.

Other constituents of the plankton are briefly reviewed; the few organisms that appear acceptable are principally algae (including filamentous blue-green algae and hystrichosphaeres), radiolaria, coelenterates (various medusae, siphonophores, and ? ctenophores), small inarticulate brachiopods, conodonts, possibly certain small trilobites, and small orthoconic nautiloids.

The suggestion that graptolites lived at various depths is not accepted. Temperature, however, might well have affected their geographical distribution.
Nemagraptus gracilis
and
Monograptus turriculatus
range from nearly 40° s to about 75°
n,
but if related to latitudes indicated by palaeomagnetic evidence, both approximate more closely to a warm-temperate or tropical zone. Relation to ‘pre-continental drift’ positioning of the Americas introduces anomalies.

Further work on the distribution-patterns of individual graptolite species may provide evidence on the presence of an early Atlantic Ocean; failing this, the central parts of various geosynclinal seas would provide the only indication of epipelagic regions (other than the Pacific) throughout the Lower Palaeozoic.
Columnar buchites at Apsley, Tasmania
Authors: SPRY ALAN H. , SOLOMON MICHAEL
Published: October 2009

Columnar jointing occurs in metamorphosed Triassic sandstones (buchites) adjacent to a Tertiary basalt neck. The buchites contain cordierite, spinel, mullite, tridymite, corundum, and up to 65 per cent glass. The temperature of metamorphism reached approximately 1000° c at a pressure of probably about 50 kg/cm
2
. Repacking of the grains in the sandstones, made possible by shrinkage of clays and development of a liquid phase, caused the contraction that gave rise to columnar jointing. A complex isotherm pattern and other factors resulted in considerable variation in the size and orientation of the columns.
DISCUSSION OF PAPERS PUBLISHED IN PREVIOUS PARTS OF THE
QUARTERLY JOURNAL
Authors: Hutchison C. S.
Published: October 2009

From Dr B. J. W
alton
:

A similar association is present north of Narssarssuaq, South Greenland (Walton, in the press). In this area there are two large intrusive complexes comprising noritic gabbros, hypersthene-augite- and hornblende-bearing diorites, and hypersthene-monzonite. These are clearly younger than the main phases of regional metamorphism, folding, and granitization but slightly older than an extensive phase of granitic development. The younger granite forms very large bodies and invades the basic rocks. The basic-intermediate rocks constitute an appinitic suite with close similarities to the Caledonian intrusive complexes of Scotland. With reference to the Caledonian fold-belt and to the orogeny which developed in Ketilidian (Pre-Cambrian) times in South Greenland, these bodies are best described as late-orogenic, using the term
orogeny
to refer to the complete sequence of events in the development of the fold-belt.
Tyrrell (1955)
showed that these rocks occupy a characteristic position in the tectono-igneous cycle. There is evidence that in South Greenland the basic rocks were intruded almost contemporaneously with the younger granites rather than during the geosynclinal phase, as suggested by Hutchison for the Singapore association. It seems likely that these rocks are characteristic of the epeirogenic uplift phase of an orogeny. Tensional conditions could prevail in part during this phase, which would allow introduction of simatic basaltic material. Extensive contamination by sialic material may cause the development of the appinitic suite. The younger granites are probably mainly palingenetic in origin.
The stratigraphy and structure of the Silurian (Wenlock) rocks south-east of Hawick, Roxburghshire, Scotland
Authors: Warren P. T.
Published: October 2009

From Dr R. B. Rickards:

Work on the Cautley area undertaken during the last few years, and completed since the reading of Dr Warren's paper, has shown that the graptolite zones recognized by Watney & Welch (1911; and see Warren 1964, p. 207) are in need of considerable revision.

Cyrtograptus rigidus
of Watney & Welch is very close to
C. symmetricus
Elles (1900
). But it has been shown that the latter species is conspecific with
C. rigidus
Tullberg (
v
.
Gortani 1922
); and this has been confirmed by other workers (e.g.,
Bouèek 1933
). The species described by
Elles (1900)
and Elles & Wood (1913) as
C. rigidus
is distinct from
C. rigidus
Tullberg (1883)
and has been renamed
C. ellesi
by Gortani (op. cit.). The zones established by Elles in the Welsh Borders, therefore, now read, from the base up:
C. murchisoni, M. riccartonensis, C. rigidus, C. linnarssoni, G. ellesi, G. lundgreni
(see
Bouèek, 1933
;
Evans 1961
).

However, although
rigidus
sensu Watney & Welch is very close to
rigidus
Tullberg, it is intermediate in some characters between the latter and
C. ellesi
Gortani. Furthermore, as shown below, it occurs at an intermediate horizon, namely the zone of
C. linnarssoni,
and may represent an evolutionary stage leading from
rigidus
Tullberg to
ellesi
Gortani. Its intermediato nature was appreciated by Watney & Welch (1911, p. 234) and also by Elles herself, since a specimen in the Sedgwick Museum (a 22459) presented by Wood, is labelled '
C. symmetricus
mut.
cautleyensis
Elles MS'.

The
Post-Jurassic erosion-surfaces in eastern Kenya and their deformation in relation to rift structure
Authors: SAGGERSON EDWARD PHILLIPS , BAKER BRIAN HOWARD
Published: October 2009

Remnants of three cyclic erosion-bevels (the end-Cretaceous, sub-Miocene, and end-Tertiary) of eastern Kenya are described. The nature and magnitude of the crustal movements—epeirogenic uplift, inland upwarping, and coastal down-flexing—that terminated the erosion-cycles are estimated and are related to contemporaneous warping and faulting in the Gregory Rift Valley and in the southern coastal zone; they are also related to coastal sedimentation and other geological events. An estimate is made of the sedimentary contents of the lower Tana basin, a coastal downwarped area.
Tectonics of the Caledonides of part of Nordland, Norway
Authors: RUTLAND RUPERT WILLIAM ROYE , NICHOLSON ROBIN
Published: October 2009

The tectonic pattern of an area approximately 100km by 40 km in the interior of the Caledonides in Nordland is described. Detailed studies of a part of the area by a number of workers are used to provide a provisional tectonic interpretation of the whole.

The region is shown to consist of two ‘internal’ basement complexes separated by a tectonic depression in which higher structural units are preserved. The basement complexes show nappe tectonics and the Pre-Cambrian gneisses in the nappe cores have been completely ‘Caledonized’. The main nappes recognized belong to the second period of deformation (F
2
) and their movement was directed towards the main tectonic depression from both sides.

The basement areas are shown to be essentially anticlinal and some of the major synforms in the area are shown to be the ‘drooping’ closures of anticlinal
nappes de recouvrement.

An earlier period of deformation (F
1
) is revealed by some major isoclinal folds that have east-west trending axes like the
F
2
nappes. The
F
l
deformation appears to have been largely conjunctive (i.e., to have preserved the major stratigraphical relationship), but one major disjunctive
F
1
nappe complex has been recognized. This upper nappe-complex may be equivalent to the Rödingsfjåll nappe in Sweden. The base of this complex is made up of granitized schists and gneisses, which are succeeded by rock groups stratigraphically equivalent to those in the lower nappe-complex.

The main tectonic depression between the basement complexes is regarded as a continuation of the Sulitjelma tectonic depression, which lies between the ‘external’ basement complexes on the Swedish-Norwegian frontier zone. The relation of the region to the Swedish thrust-zone is briefly discussed and comparisons are made between the structures recognized and those recently described from the Scottish Highlands.
A reinterpretation of the breccias in the Meneage crush zone of the Lizard boundary, south-west England
Authors: LAMBERT JOHN LEWIS MACKENZIE
Published: October 2009

Breccias exposed north of the Lizard boundary in east Meneage have hitherto been regarded as tectonic in origin, and the area occupied by them has been called the
Meneage crush zone.

The characters and relations of the rocks of this zone are most clearly seen in the coast section between Nare Point and Porthallow. Unstratified clastic sedimentary rocks that make up the bulk of this section consist of four divisions: siltstone breccia, slate with phacoids of greywacke, conglomeratic pebbly slate, and conglomerate. Somewhat similar rocks are poorly exposed inland and are also found at one locality on the west coast of the peninsula.

The rocks have been deformed tectonically but it is concluded that their lack of stratification is due to a process that operated soon after deposition, most probably subaqueous slumping. There is no evidence to support the hypothesis of large-scale northward thrusting of the Lizard series.