Blocks of medium-grained granodiorite to 4 m, and minor diabase, quartz diorite, granite, aplite and granophyre, are common in ejecta of the ∼6,900 yrBP calderaforming eruption of Mount Mazama. The blocks show degrees of melting from 0–50 vol%. Because very few have adhering juvenile magma, it is thought that the blocks are fragments of the Holocene magma chamber's walls. Primary crystallisation of granodiorite produced phenocrystic pl + hyp + aug + mt + il + ap + zc, followed by qz + hb + bt + alkali feldspar (af). Presence of fluid inclusions in all samples implies complete crystallisation before melting. Subsolidus exchange with meteoric hydrothermal fluids before melting is evident in δ18O values of −3·4+4·9‰ for quartz and plagioclase in partially melted granodiorites (fresh lavas from the region have δ18O values of +5·8−+7·0‰); δ18O values of unmelted granodiorites from preclimatic eruptive units suggest hydrothermal exchange began between ∼70 and 24 ka. Before eruption, the granitic rocks equilibrated at temperatures, estimated from Fe-Ti oxide compositions, of up to ∼1000°C for c. 102–104 years at a minimum pressure of 100-180 MPa. Heating caused progressive breakdown or dissolution of hb, af, bt, and qz, so that samples with the highest melt fractions have residual pl + qz and new or re-equilibrated af + hyp + aug + mt + il in high-silica rhyolitic glass (75-77% SiO2). Mineral compositions vary systematically with increasing temperature. Hornblende is absent in rocks with Fe-Ti oxide temperatures >870°C, and bt above 970°C. Oxygen isotope fractionation between qz, pl, and glass in partially fused granodiorite also is consistent with equilibration at T≥900°C (Δ18Oqz.pl = +0·7 ± 0·5‰). Element partitioning between glass and crystals reflects the large fraction of refractory pl, re-equilibration of af and isolation or incomplete dissolution of accessory phases. Ba and REE contents of analysed glass separates can be successfully modelled by observed degrees of partial melting of granodiorite, but Rb, Sr and Sc concentrations cannot. Several samples have veins of microlite-free glass 1–5 mm thick that are compositionally and physically continuous with intergranular melt and which apparently formed after the climactic eruption began. Whole-rock H2O content, microprobe glass analysis sums near 100% and evidence for high temperature suggest liquids in the hotter samples were nearly anhydrous. The occurrence of similar granodiorite blocks at all azimuths around the 8 × 10 km caldera implies derivation from one pluton. Compositional similarity between granodiorite and pre-Mazama rhyodacites suggests that the pluton may have crystallised as recently as 0·4 Ma; compositional data preclude crystallisation from the Holocene chamber. The history of crystallisation, hydrothermal alteration, and remelting of the granitic rocks may be characteristic of shallow igneous systems in which the balance between hydrothermal cooling and magmatic input changes repeatedly over intervals of 104-106 years.

In an attempt to establish a chronology for volcanic neck emplacement and so elucidate petrogenesis, isotopic studies have been carried out on various cumulate inclusions, blocks and megacrysts which occur chiefly in association with tuffs infilling several Scottish vents. K-Ar ages of 13 samples of low-pressure cumulate minerals (biotite, hornblende and pyroxene) from necks in East Fife indicate crystallisation at shallow depth at 314 Ma. U-Pb analyses of zircons are concordant at 318 Ma suggesting they are also members of this suite and their formation is penecontemporaneous with the Namurian volcanic activity which is welldocumented stratigraphically. By 295 Ma crystallisation of anorthoclase megacrysts had been completed, perhaps from the fractionated residuum. An eruption from considerable depth (within the stability field of garnet precipitation) then broke through to the surface bearing high-pressure megacrysts. This penetrated and disrupted the early cumulates carrying them to the surface and producing the diverse vent assemblages. K-Ar dating of basanites suggest that the Duncansby Ness neck in Caithness was emplaced around 270 Ma in the early Permian. For two Fife necks the balance of evidence favours an age of 290 Ma (Stephanian) for this final explosive activity associated with vent formation.

The Leadhills–Wanlockhead mining field is situated within a synclinorial belt of greywackes, bounded to the north and south by anticlinoria in which lower stratigraphical elements are exposed. The universal strike is N.E.–S.W. The southern margin of the northern anticlinorium is delimited by a strike thrust fault, inclined to the north-west. The shear zone caused by this thrust is considered to be the principal structural feature governing the localization of the ore deposits.

The complex N.E.–S.W. folding and faulting, imposed during the Caledonian orogeny, is crossed by a series of intersecting joints, whose average strike is N.N.W. The majority of the mineral veins also trend N.N.W. The formation of these discordant structural features under Caledonian stress is demonstrated by the presence of N.N.W. trending Caledonian dykes.

Sinistral movement along the joint pattern, ascribed to a reorientation of the “Caledonian” stress towards an “Hercynian” direction, resulted in the formation of open spaces on the more north-westerly trending members of the joint system in the greywacke belt. This feature is considered to be the secondary structural control responsible for the localization of the ore deposits.

Fifty-seven minerals were identified from the deposits. Fifteen of these minerals had not been previously recorded from the locality, including (1) a new chromian mineral; (2) a new variety, chromian leadhillite; (3) a mineral previously recorded only as an artificial product, lead hydroxyapatite; (4) phœnicochroite, not previously confirmed in the British Isles.

Two periods of mineralization were distinguished. The first consisted of quartz veins with which are associated small amounts of gold, pyrite and muscovite, tentatively assigned to the Caledonian orogeny, and the second comprised the lead-zinc mineralization. The paragenetic relationships of the primary minerals of the lead-zinc mineralization indicate two generations of sulphides; the second generation is accounted for by reprecipitation of elements derived from the replacement of the first generation by late stage quartz. A study of the distribution of elements through the paragenesis suggests that some elements were derived from other than a magmatic source, and that contamination has probably played a considerable rôle in the control of the character of the gangue minerals.

Evidence that the mineralizing solutions had a deep-seated origin is provided by the mineral zones and the geochemical character of the deposit. Emplacement of the minerals took place at a temperature of the order of 143°−281° C, and a depth of the order of 2000–4000 feet below the surface.

The Leadhills–Wanlockhead deposits are related to other lead-zinc deposits in Britain. On the basis of geochemical assemblage and the relation to igneous activity, it is concluded that the deposits were probably derived from the top of the tholeiitic crustal layer and the base of the granitic crustal layer, and were genetically associated with the Hercynian orogeny.

Jahns and Burnham (1969) proposed that the internal evolution of zoned granitic pegmatites could be explained by crystallisation from water-saturated melts which evolved to produce systems with a melt plus a separate aqueous fluid. Examination of microthermometric properties, chemical compositions and gas contents of solid-liquid-vapour inclusions from a number of the zones of the Tanco rare element granitic pegmatite places constraints on fluid evolution within the framework of the crystallisation history of the pegmatite, and contributes to an examination of the Jahns–Burnham proposal.

Initial crystallisation at Tanco was from the wall rock inwards, producing the relatively unfractionated wall zone (potassium feldspar–quartz-albite-muscovite). Textural evidence, and an upward increase in the level of geochemical fractionation, indicate that much, but not all, of the subsequent crystallisation of the pegmatite was from the base upwards. Inclusions trapped by wall zone and metasomatic wall rock tourmaline indicate that the pegmatite was intruded as a 2 phase alumino-silicate melt/fluid mixture at ∼720°C, with an initial fluid composition of ∼98mol.% H2O (containing 2 equiv. mo1% NaCl) and <2mol% CO2 (containing <5 equiv. mo1% CH4). These observations indicate that both melt and fluid were present from the start of crystallisation (Jahns & Burnham 1969), but show that CO2 and dissolved salts were important additional components of the fluid phase. The bulk of the pegmatite then crystallised in the range 600-470°C from melts and fluids with continued low levels of CO2 (2-3mol.%) and approximately constant salinity (∼7 equiv. wt.% NaCl dissolved in the aqueous phase). Crystal-rich inclusions, which may represent trapped alumino-silicate melts, are present throughout pegmatite crystallisation down to temperatures as low as ∼262°C. The final stages of crystallisation resulted in the formation of the beryl fringe at 291 ± 33°C and the lower part of the quartz zone at 262 ± 29°C. By the later stages the fluid had cooled through an H2O-CO2– dissolved salt solvus resulting in H2O-CO2 phase separation. Gas chromatographic analysis of the fluid components in the vug quartz, beryl fringe and lower part of the quartz zone shows that the inclusions contain H2O, CO2, CH4, N2, CO, Ar, and trace C2H6 in the beryl fringe. Measured CH4:CO2 ratios of 0·0060 (±0·0015) for the beryl fringe (twenty crushes on five samples) and 0·0042 (±0.0021) for the quartz zone (thirty crushes on six samples) yield fO2 estimates of 1×10−36 and 2 × 10−38, respectively, which are just above QFM at these temperatures.

Narrow, intermittent, fault-bounded outcrops forming the largely Ordovician Highland Border Complex comprise terrigenous-derived turbidities, a dismembered ophiolite, and ophiolite-derived sediments.

New major- and trace-element analyses of the mafic igneous rocks confirm that two main groups exist. One, represented in outcrops the length of the Highland Boundary fault-zone, has a mostly MORB-like chemistry with some trace-element compositions conventionally pointing to genesis above a subduction zone. The other group, found more locally, has an alkalic ‘within-plate’ character. Amphibolites interpreted as ophiolitic ‘sole’ rocks are chemically similar to the MORB-type mafic extrusive rocks. X-ray diffraction of the sedimentary rocks reveals kaolinite to be widespread and this is attributed to tropical weathering of the Highland Border Complex beneath a (?mid-Devonian) unconformity surface. New major- and trace-element analyses show that the turbidities of the Highland Border Complex were derived from a terrigenous terrane similar to that which supplied the Dalradian Supergroup. Inter-lava sediments reflect varied terrigenous (distal turbidites), hydrothermal (iron oxide sediments), mafic extrusive (volcaniclastic silt) and biogenic (jaspers) provenances. The ophiolite-derived Highland Border Complex sediments also have a terrigenous component. Unlike, for example, the early Ordovician rocks of the South Mayo trough (Ireland), coeval differentiated volcanic material is not a significant component of the Complex.

No one existing model adequately explains all the available data. We favour an origin of the Complex in the Ordovician as a small Gulf of California-type marginal basin which was later tectonically emplaced in stages involving a long history of alternating extension, strike-slip and compression.

Two new species of fossil seeds are described from the Cementstone Group of Berwickshire. Deltasperma fouldenense is asymmetrically platyspermic, and has large superficial cells chiefly on the more convex side. It is orthotropous but shows no pedicel. Camptosperma berniciense is campylotropous and has a dense integument. A vascular bundle to the chalaza ends at the nucellus base.

Both seeds possess a similar lagenostome and short salpinx; two integumental bundles which expand in the free lobes; a female prothallus with a wide “tent-pole” and about two archegonia; a nucellus adnate to the integument below the lagenostome; and spherical pollen grains in the pollen chamber. The seeds show most affinity with the Lagenostomales.

The present work on Apseudes talpa forms the second and concluding part of an investigation undertaken in an attempt to discover from feeding mechanisms the steps by which the higher Peracarida may have been derived from a primitive Mysid-like ancestor. The first part of the work consisted of an account of the feeding mechanism of Diastylis bradyi (Dennell, 1934), but it was felt at that time that a discussion of its significance could usefully be postponed until the completion of the work on Apseudes. It is now possible, in view of the accounts of feeding in Hemimysis (Cannon and Manton, 1927), and in Gnathophausia and Lophogaster (Manton, 1928), to discuss with some measure of completeness the feeding mechanism of the Peracarida.

An interpretation of the Tertiary rocks of the area, which are shown to be denudation relics of a gigantic volcano, is found by following the actualistic principle, that is by interpreting the unknown with reference to the known or actual. “Actualistic”, i.e. with reference to actual causes—commonly used by continental geologists—is chosen in preference to “uniformitarian” since the latter stands in contradistinction to “catastrophic”, and is not, therefore, altogether appropriate to some of the more violent aspects of volcanic activity. Gabbros and granophyres, hitherto thought to be plutonic intrusions emplaced within Caledonian granodiorite, are shown to be highly metamorphosed basaltic and rhyolitic lava-flows, agglomerates and tuffs, together with some gabbro sills. These rocks form a layered series which is almost horizontal at Slieve Gullion, and dips at various angles at Foughill and Carrickcarnan. A Tertiary ring-dyke of granophyre and felsite encircles the layered rocks and outlines a caldera within which the basaltic lavas (including pillow-lavas) of Slieve Gullion accumulated. During the formation of a later caldera these lavas became inset within the underlying Caledonian granodiorite. The acid layers of Slieve Gullion represent rhyolites, incandescent tuff-flows, and agglomerates, the materials of which were derived from the Caledonian granodiorite. The time of eruption of these acid rocks is correlatable with periods of caldera formation.

The layered series is dissected by arcuate faults, and contacts previously thought to be intrusive are now demonstrated to be faulted. Transgressive granophyres follow the faults and form intrusion-breccias and net-vein systems with the layered series. Evidence is presented for concluding that these granophyres originated as glassy acid tuffisite—an intrusive pyroclastic rock (Cloos, 1941)—derived from the basement Caledonian granodiorite, and emplaced by rising gas-streams. That the gas sometimes had a temperature high enough to fuse basalt is witnessed by the fact that the basaltic rocks commonly become exceedingly fine grained where they adjoin transgressive granophyre. Such fine-grained edges are cross-cutting to the layers and cannot therefore be interpreted as normal chilled edges. Hybrid rocks, e.g. marscoite, are associated with the transgressive granophyres. They are shown to represent mechanical mixtures of acid tuffisite, carried upwards by rising gas-streams, with fragmented (tuffisitised) and partially fused basic material derived from the walls of the channels. The transgressive granophyres and associated hybrids are related in origin to incandescent tuff-flows, and are regarded as marking the routes by which such flows reached the surface.

The metamorphism of the basaltic flows, and the transformation of the acid layers and transgressive acid tuffisites to granophyre, were probably accomplished during the pneumatolytic and hydrothermal phase of volcanic activity. Transformation of the acid rocks to granophyre involved introduction of K and Si, and removal of Na, Al, Fe, Ca, Ti, P and Mn. Similar chemical interchanges transformed basaltic rocks at Foughill and Carrickcarnan to quartz-dolerites. The subtracted materials have been located in small-scale basic fronts margining granophyres; within masses of gabbro that sank within gas-tuff streams from higher levels; and in dispersed form within the basic rocks of Slieve Gullion.

The existence in Mexico of blight-resistant species of potato has been known for many years, but they occur in the wild and are quite unsuitable for agricultural purposes. In order to utilise their resistance to disease it is necessary to combine disease resistance with the cropping qualities of cultivated forms while eliminating the undesirable characters which are prominent in the wild forms. Breeding work with this object in view has been in progress at the Scottish Plant Breeding Station for several years, and results obtained in the course of testing progenies for reaction to blight infection are discussed in the following pages.

The early Cambrian Chengjiang biota in Yunnan, southern China has yielded many articulated exoskeletons of the spiny redlichiid trilobite Eoredlichia intermedia, of which some have their appendages exceptionally well preserved. Both of the paired uniramous antennae of a medium-sized holaspis consist of 46–50 short segments (articles), each of which bears a fine spine near its inner edge. Behind the antennae there are twenty-one pairs of biramous limbs: three pairs are situated underneath the cephalon, one pair underneath each of the fifteen thoracic segments, and probably three pairs underneath the small pygidium. The endopod consists of a broad basis and seven podomeres, of which the last is divided into three terminal spines. The exopod is blade-like, and according to one interpretation, is dorsally hinged to the basis of the endopod; an alternative suggestion being that both the endopod and exopod are split from the basis, the latter being independent and not forming part of the endopod. The exopod has a prominent anterior rim, and possesses about forty long filaments along the posterior margin, and short setae along the rounded distal lobe. The basic appendage features of the redlichiid trilobites, and likewise the gut, are comparable to those of other known Cambrian polymerid trilobites that belong to more distantly related clades.

The Carboniferous trilobite Paladin eichwaldi shunnerensis (King 1914), at its type locality in northern England is exceptionally well-preserved, and shows all stages of growth from the degree 0 meraspis onwards. The post-protaspid ontogenyis described here with particular reference to the development of cuticular sculpture. On the dorsal surface of the smallest specimens a polygonal network of raised ridges (cell polygons) is apparent. With size increase, granules progressively appear amongst the polygons, which in turn change into large tubercles as the polygonal network fades. As the trilobite grows into an adult, the tubercles become relatively smaller, and pits, the openings of cuticular canals, appear amongst them. Marginal terrace lines become pronounced. On the hypostome, however, terrace lines become effaced centrally, while large pits develop. In the early meraspis the eyes are “schizochroal”, but the lenses rapidly become closely packed and contiguous and the eye is soon of “holochroal” type. The meraspid phase is passed through very rapidly. Whereas the earlymeraspis could not enroll, its pygidium could be bent down vertically, and this facility might have allowed the larva an escape reaction.

Isotope ratios of elements such as Sr, Nd, Pb and Hf can be used as tracers of magmatic sources and processes. Analytical capabilities have evolved so that isotope ratios can now be analysed in situ, and isotopic tracers can therefore be used within single minerals to track the changing magmatic environment in which a given mineral grew. This contribution shows that Sr isotope ratios in feldspars that make up plutonic rocks will typically preserve initial isotopic variations, provided precise and accurate age corrections can be applied. Variations in initial isotope ratio can give a core-to-rim record of magmatic evolution and can be used to diagnose open system events such as contamination and magma recharge and mixing.

New single grain Sr isotope data are presented from the Dais Intrusion, Antarctica, which reflect an open system origin for the crystals. The crystal cargo appears to be aggregated and assembled during transport and emplacement. This model, as opposed to a magma body crystallising post emplacement, may be more applicable to plutonic rocks in general, and is testable using the in situ isotopic determination methods described here.

Holocene sea-level changes affected people living in the Pacific Islands and their ancestors along the western Pacific Rim. Sea-level changes, particularly those that were rapid, may have led to profound and enduring societal/lifestyle changes. Examples are given of (1) how a rapid sea-level rise (CRE-3) about 7600 BP could ultimately have led to the earliest significant cross-ocean movements of people from the western Pacific Rim into the islands; (2) how mid to late Holocene sea-level changes gradually created coastal environments on Pacific Islands that were highly attractive to human settlers; (3) a hypothesis that rapid sea-level fall during the ‘AD 1300 Event' brought about widespread disruption to trajectories of cultural evolution throughout the Pacific Islands; and (4) the effects of recent and likely future sea-level rise on Pacific Island peoples.

This is a study of the functional morphology of the muscular and reproductive systems of the adult beetle, Atomaria ruficornis (Marsham) made by means of serial sections and dissections. An account is given of the skeleto-muscular system of the head, thorax and abdomen with reference to previous work in this sphere. Wherever possible, the muscles described have been homologized with those of other Coleoptera. In a small number of cases, it has been found necessary to use new names for muscles. The probable mode of action of the mouth-parts and foregut during feeding is described. An account is given of the reproductive organs and genitalia of both male and female beetles; the muscular system of the genitalia in both sexes is described fully, and the functioning of the genitalia is discussed.

In a recent paper (Gordon, 1938) reasons were given for the belief that semi-arid conditions prevailed during Lower Carboniferous times in the neighbourhood of North Berwick, East Lothian. The evidence was opposed, in a measure, to that advanced by Mr George Barrow in the East Lothian Memoir (1910) to substantiate the same position. He had relied on the absence of fossils as part proof; but, in point of fact, fossil plants have been obtained in abundance from the actual bedded ashes of Oxroad Bay that he considered (a) to be unfossiliferous, and (b) to have been formed in a manner similar to beds on the Springbok Flats of the Transvaal. The plants that have now been obtained showed xerophytic features, and, consequently, a semi-arid climate was proved on positive evidence. Other positive evidence of a lithological character was also presented in confirmation (Gordon, 1938, pp. 352, 353).

The unique specimen of Coccosteus angustus Traquair, from the Lower Devonian Hunsrückschiefer of Germany, is redescribed and referred to Gemuendenaspis n.gen. Previously unrecorded details of its morphology and a reconstruction are given. Its possession of both arctolepid and brachythoracic characters is confirmed and it is suggested that Gemuendenaspis should be referred to the family Gemuendenaspidæ nov., which closely approaches what would be expected in ancestors of the Coccosteidæ.

A batholith of around 10,000 km2 was formed during the Hercynian orogeny in the Spanish Central System (SCS). Geochronological data indicate concentrated magmatic activity during the period 325-284 Ma. This late-orogenic magmatism is essentially granitic with only minor associated basic rocks (< 2% in outcrop). The SCS is a remarkably homogeneous batholith showing a restricted range of geochemical granite types without any evolutionary pattern related to time. These peraluminous granites show a limited variation in Na2O/K2O) (0·60-0·95), K/Rb (140-240), (La/Yb)n (6-13), and Eu/Eu* (0·34-0·62) ratios. This constancy in chemical characteristics is also reflected in their isotopic signatures: most monzogranites have initial 87Sr/86Sr ratios in the range of 0·7073-0·71229, initial εNd values vary between —5·4 and —6·6 and δ 18O values group in the restricted range of 8·9-9·6‰. The lack of significant differences among SCS granitoids, maintained during a long geological period, suggests constancy in the nature of their source regions and conditions of magma generation. (1) Limited range of crustal sources: an essentially magmatic recycling during Hercynian orogen is suggested. Mantle-derived components are very limited and restricted to a minor role in the origin of the batholith. Geochemical and isotopic features of SCS granitoids are compatible with felsic lower crustal sources. (2) Constraints in melt conditions: uniformity in residual mineral assemblages (feldspars and garnet are always present in the granulitic residua) combined with a lack of attainment of equilibrium conditions during accessory phase dissolution in the crustal melting process is suggested. Granitic melts never reach saturation in some trace elements (REE, Th, Y, Zr), restricting their chemical variability. (3) Homogenisation in magma chambers: long-lived magmatic systems whose successive pulses accumulate into large magma chambers have the opportunity to mingle, thus reducing source differences.

The Criffell pluton in southwestern Scotland (397 Ma, a Newer Granite of late Caledonian age) is concentrically zoned with outer granodiorites of typically I-type aspect passing into inner granite with more evolved characteristics. The zonation is examined in terms of the compositional surfaces of bulk parameters such as SiO2 and Rb/Sr and compositional variation is best modelled as multi-pulse, there being greater variation in bulk composition between pulses than within pulse. Published variations in Sr, Nd and O isotopes reflect the derivation of the pulses from separate and isotopically distinct sources. Other evidence for open-system behaviour includes mingling with mafic magmas to form enclaves, whereas closed-system behaviour is indicated by restite separation in the early granodiorites, and fractional crystallisation in the late granites. A dominant infracrustal I-type magma formed the first pulse followed by magma derived from more evolved crustal rocks (mainly metasediments of varying ages and maturities). Experimental fluid-absent melting of amphibolite and metapelite at about 900°C has shown that significant quantities of melt can be generated, respectively with I-type and S-type characteristics. Despite having similar bulk compositions, these melts have very different viscosities and densities for the same H2O contents (ηS-type>ηI-type and ρS-type≤ρI-type). It is argued that the rheological controls on magma escape from the source region along complex and tortuous pathways favour the more fluid I-type melts over the more viscous (and only slightly less dense) S-type melts. This constraint could have the effect of reversing the expected buoyancy-driven emplacement sequence, and may represent an alternative rheological differentiation mechanism for the formation of some zoned plutons.

The fauna of the Polar regions is of deep interest to zoologists generally, that of the Antarctic specially so, and in this the Rhizopodist can justly claim his share.

Since the return of the Challenger Expedition in 1876, the later British expeditions to this area, with the exception of the Scottish National Antarctic Expedition, did but little in the way of sounding and trawling in the deeper waters of the Antarctic. Although much additional work has been carried out, and many new and rare species of the higher forms of marine life from this region have been brought to light, comparatively little has been added to the Rhizopod fauna since the results of the Challenger Expedition were published. The following pages on the Foraminifera are due to the energy and enthusiasm of Dr W. S. Bruce, F.R.S.E., and his colleagues. The genera and species here enumerated and described have been obtained from samples of deposits sent to me at intervals by Dr Bruce and Dr J. H. Harvey Pirie, collected by them, during the S.Y. Scotia Expedition in 1903-4, chiefly from the area of the Weddell Sea, where the ocean floor is covered with terrigenous deposits of Blue Mud, or (as Dr Pirie calls them) Glacial Muds and Clays.

Hyalotuff deltaic deposits, a high proportion of volcanogenic sediment and a repeated occurrence of conglomerate with well-rounded clasts constitute evidence for the shallow-water origin of spilitic lavas and volcanogenic sediments in an Ordovician ophiolite at Ballantrae, SW Scotland. One section, >1.5 km thick, shows repeated evidence for a shallow-water origin. This implies accumulation in a subsiding area. In this sense the sequence at Ballantrae is in marked contrast to those found in oceanic islands (hot spots) which are known to grow from deep into shallow water. Neither does it compare well with those from ocean ridges which usually begin in deep water and move, with cessation of vulcanicity, into even deeper water.

The lava sequence at Ballantrae compares well with oceanic island-arc and remnant arc deposits where uplift and subsidence is common. This, the occurrence of intermediate and acidic lavas and clasts, and the restricted palaeontological and radiometric ages support an arc-marginal basin origin for the lavas. Diversity in the chemical composition of the lavas may reflect diverse origins within the marginal basin.

An upward coarsening sedimentary sequence was built by a hyalotuff delta which formed in front of advancing lava flows. As the lavas advanced over the sediments so a sequence was generated where these sediments have a source in lava flows which were eventually to overlie them.

Clasts of tholeiite were derived from lavas which are now spilite. This, together with the presence of spilitic lava clasts and tuff immediately beneath the flow suggests that the spilitisation resulted from metasomatic activity associated with the convective circulation of trapped water, with the lava as a heat source.