Grain size characteristics of the sediment and the flow stage characteristics of the river are the two most important factors influencing sedimentation in the channel zone. Climate is important in its influence on floodplain (overbank) sediment.

Supra-bar platform (upper) parts of mature bars from a wide range of climatic conditions consistently show a sequence in the development of contained sedimentary structures which is related to the flow stage. At high stage, in rivers where the bed materials are quite mobile, the bar form is not thought to be present: the form develops on the falling stage, and the bar is dissected on the lowest stage. The various bar forms have a related diagnostic structure which determined from the nature and distribution of the stratification types, and the manner of their deposition on the falling flow stage. The exposed (supra-platform) parts of lateral bars have a side and longitudinally filled inner channel which comprises fine sediment. Medial bars have converging cross-strata in sands which are overlain partly by gravels in an upward coarsening sequence.

Lateral migration of the channel zone, brought about by the preferential bar accretions to one side, results in building of a lithosome, the facies structure of which is partly determined by the nature of the bar accretions. As the channel migrates the abandoned bars may be covered with fine sediments so as to build up an upward fining sequence. The nature of the fine overbank part of the braided stream cycle is as complex as the coarse lower, so that a highly variable vertical sequence of lithological types is likely to be constructed.

Upward fining cycles are also built by some fine braided streams but they are the product of a single flood rather than lateral channel migration. Braided stream deposits are distinguishable from those of small, coarse meandering stream deposits by the presence of inner accretionary banks in the latter, and inner channels in the former.

Skeletal remains of Tristychius arcuatus commonly occur in ironstone nodules from the Scottish Upper and Lower Oil Shale Groups. This material is clearly distinguishable from the small shark from Glencartholm described by Traquair, Woodward and Moy-Thomas under this name. Study of the latter shows that its finspines are distinctly different from the holotype of T. arcuatus and, therefore, it has been renamed.

Tristychius arcuatus sensu stricto is a medium-sized hybodont shark with a short gape, a functionally heterocercal tail and narrow-based, tribasal pectoral fins. Its most unusual feature is a well developed opercular gill cover composed of long hyoid rays. Evidence suggests that this character was present in several Palaeozoic sharks, although it is absent in all Recent elasmobranchs. It is not clear whether it was primitively present in chondrichthyans or evolved separately in several lineages.

Hybodonts and ctenacanths are recognised as separate, specialised shark radiations, neither of which can be directly ancestral to Recent sharks. Of the two, hybodonts appear to be more closely related to Recent forms, although the presence of typical hybodont finspines in Tristychius arcuatus indicates that they had diverged from ancestral euselachians before the beginning of the Carboniferous.

Two pairs of detached fossil cupules from the Cementstone Group of the East Lothian coast are described. One pair (specimen 1) contains 16 ovules agreeing with the seed genus Hydrasperma Long as well as 8 microsporangia containing spores. The second pair (specimen 2) has neither ovules nor microsporangia.

The ovules present in specimen 1 have about 9 free apical tentacles and as many longitudinal ridges on the bodies of the ovules. The central column is very well developed, about as long as the ovule body and obconical in shape. In it some of the cells have bars of thickening on the walls like transfusion cells. Each cupule-pair has a common stalk which divides to become the two inverted cupules. In specimen 1 each cupule has a wall consisting of two valves united above but subdivided into tapering lobes below, i.e. distally. Ovules are borne below the concave upper region of each cupule (sessile laminar placentation). In this specimen each cupule-valve is subdivided into two smaller portions, one of which bears 8 microsporangia. The latter appear to be terminal and reflexed and almost sessile.

The laminar placentation in Hydrasperma supports the view that this type of placentation in angiosperms is primitive and the bisexual cupule-pair here described suggests that the primitive fertile fronds from which cupules (and presumably carpels) evolved were originally capable of bearing both mega- and microsporangia.

Past work on the genus Pitus is reviewed and evidence adduced in favour of the view that it was a genus of arborescent Pteridosperms bearing the sterile bifurcate fronds known as Lyginorachis papilio Kidston. These probably resembled Sphenopteris affinis L. & H. in the compression state. Fertile organs were probably borne on trifurcate fronds in which a stemlike median rachis (Tristichia ovensi Long) bore synangia (Telangium sp.) composed of eight microsporangia, or alternatively seed-cupules of Stamnostoma huttonense Long. Branching in Pitus produced single branches at a wide angle, or pseudo-whorls (close spirals) of about five branches. An anomalous ring of medullary xylem was sometimes associated with branching as in Lyginopteris. This supports the view that Pitus should be classified in the Lyginopteridaceae although it was arborescent and in some respects more advanced than many of the more shrub-like Pteridosperms.

On the western and eastern sides of the North Atlantic craton, rocks between about 1·7 b.y. and 1·2 b.y. old are represented by thick basinal assemblages. Thin platformal successions cover the intervening region. The clastic component of these rocks was largely derived from the southeast where the Elsonian orogen might have been an important source terrane. Widespread mafic igneous activity (about 1·2 b.y. ago) in the central platformal region preceded orogenic movements in the basinal areas (Racklan-Carolinidian-Grenville orogeny). The Grenville orogen may have contributed significant amounts of clastic debris for a second cycle of sedimentary accumulation(∼ 1·2 b.y.–∼ 0·8 b.y.). The upper part of this cycle typically contains red beds and evaporites and, in the North American Cordillera, shows evidence of contemporaneous block faulting and extensional tectonism. These movements culminated in the East Kootenay and Hayhook orogenies and ushered in a third period of deposition about 850 m.y. ago. The third sequence includes glaciogenic rocks in the Cordilleran and East Greenland geosynclines. The basic geotectonic elements (platforms and geosynclines) of the North Atlantic craton were established as much as 1·7 b.y. ago, but continental fragmentation on the borders of the craton may not have taken place until early Phanerozoic times.

Numerical taxonomic methods are applied to the Encrinurinae (Trilobita). Thirty-five cranidial and pygidial attributes are defined of which some (e.g. those relating to the glabellar tubercles) are specific to encrinurines and cybelines while others have application to non-encrinurids. Of nearly 200 named species of Encrinurinae only about one-third have been described in the literature in sufficient detail for their cranidial and pygidial attribute states be coded: a much smaller proportion of species is well enough known for librigenal, rostral, hypostomal and thoracic attributes to be coded. A comprehensive numerical taxonomy of the subfamily must therefore await detailed description of most of the known species. A list is given of encrinurine species in need of re-investigation. Meanwhile, 63 species can be coded for 34 attributes, and 75 species for 28 attributes. Principal components analysis is used to produce ordinations of these species. The minimal spanning tree superimposed on the ordination suggests possible evolutionary lineages. Ordination of the attributes is by non-linear mapping based on a distance matrix derived from the inter-attribute correlation matrix by the transformation (tanh−1 |r|)−1. The ordinations compare well with subjective assessments of relations and phylogenies.

Four new petrified specimens of cupules assigned to Hydrasperma cf. tenuis Long are described from the Cementstone Group of Oxroad Bay, East Lothian. In one of these specimens four ovules are present. Three of the specimens are interpreted as representing a pair of cupules derived from a single megasporophyll showing dichotomy so that each cupule is termed a hemi-cupule and has two lobed halves which represent quarters of the entire megasporophyll. In the fourth specimen five cupules are present, each possessing two lobed halves not sub-divided into quarters. Hydrasperma is thus interpreted as showing two kinds of cupules designated mega-cupules and paired hemi-cupules. The theory is developed that angiosperm carpels have evolved from the two kinds of pteridosperm cupules.

Six new specimens of petrified cupules of Hydrasperma cf. tenuis from Oxroad Bay, East Lothian (Cementstone Group) have been examined. Sections of one show a close similarity in size and shape to compressed cupules of Sphenopteris bifida L. and H. from the Lewis Burn (Scremerston Coal Group or lower Viséan) of Northumberland. The conclusion reached is that cupules of Hydrasperma cf. tenuis Long are petrified equivalents of the compressed cupules of Sphenopteris bifida L. and H. The morphological significance of this identification is discussed.

The structure of the fishes constituting the Devonian genus Cheirolepis is investigated. Articulated remains from the Scottish Old Red Sandstone and the Canadian Upper Devonian were studied and two species are recognised, the Middle Devonian C. trailli and the Upper Devonian C. canadensis. Recently described fragmentary material from Europe assigned to the genus is best regarded as incertae sedis. Cheirolepis is the earliest actinopterygian genus with extensive material. Neurocranial remains are described, with a crossopterygian-like parasphenoid. There seems to have been a mobile rostral region with several small bones between premaxilla and postrostral extending to the anterior corner of the small dermal orbit. New palatoquadrate and pectoral girdle material is described. The apparently primitive nature of the head skeleton is related to the cranial dynamics and the likely mode of life. The small scales and the elongate-fusiform body shape are a corollary of the method of swimming. The ecology of the fishes is touched upon. A taxonomic investigation of the two species was carried out but although interesting variation in the scale-row numbers came to light no changes at the specific level were deemed necessary. Revised generic and specific diagnoses are given.

Mitrospermum bulbosum sp. nov. is described from a single specimen found in the Lower Carboniferous Cementstone Group of Berwickshire. It is a platyspermic seed about 14 mm diameter. The nucellus is free from the integument laterally and contains a single megaspore above which is a pollen chamber and well-developed apical beak. The integument is cordate at the base around a bulbous chalazal region with two membranous wings which terminate above as two flat lobes having a V-shaped sinus between. At the base of this sinus is the micropyle which surrounds the apex of the nucellar beak.

Mitrospermum compressum Arber has been re-investigated from 21 specimens and evidence adduced to show that the micropylar canal expands upwards and opens between two short apical lobes.

Conostoma oblongum Will, has been re-investigated from 20 specimens. It possesses four integumental bundles; sometimes there are two basal lobes but no integumental flanges; no free apical lobes have been seen and the seed was sessile, not having a wide pedicel.

A specimen of Lagenostoma ovoides Will, with a mature prothallus is briefly described from longitudinal sections. At the upper end the prothallus has three archegonia and a circular trough surrounding the ‘tent-pole’.

The limpet Acmaea virginea is an important agent of erosion of bivalve shells within the photic zone. This lower limit is governed by the depth range of shell-boring algae on which it feeds, the dominant alga being conchocelis. Any authigenic ferromanganese coatings on shells are removed by the grazing and the shells may become wafer thin and highly fragmented. The chiton Lepidopleurus also grazes shell surfaces but feeds more on superficial detritus than on the boring algae, and so its depth range is not so restricted. Both molluscs leave highly distinctive radula marks on shells which are potentially preservable in the fossil record. Acmaea virginea produces broad scoops, six-pronged, with very sharp narrow interstitial ridges. Lepidopleurus produces short, sharp scratches in sets of two, three or four, with wide interstitial ungrazed plateaux.

The faecal pellets of both species contain 5–10 μm sized carbonate particles. Whereas there is little else in Acmaea pellets, which are white, cylindrical and only loosely held together, chiton pellets include much fine manganiferous material, detrital quartz and broken diatom frustules, and are well bound with mucilage which makes them dirty brown-grey in colour and ovoid. The data indicate that physical processes need no longer be assumed to be the major factor in the recycling of carbonate from shells, and in their fragmentation.

Eurypterids of the Superfamily Stylonuroidea Diener 1924 sensu Størmer (1974, 373) from the Pentland Hills, Midlothian, are redescribed and the evidence which these forms may give concerning the life environment of the Gutterford Burn Eurypterid Bed (Upper Llandovery), from which most of them have been obtained, is considered. Five species are recognised. Parastylonurus ornatus (Laurie) is redescribed with special reference to the organs of locomotion and reproduction. A new form from the Gutterford Burn is described as Parastylonurus hendersoni sp. nov. Stylonurus macrophthalmus Laurie is designated the type species of the new genus Hardieopterus and Stylonurus knoxae Lamont as the type species of the new genus Lamontopterus. The unique holotype of Lamontopterus knoxae is of morphological interest in showing evidence of the gut.

Stylonuroids from other Scottish Silurian localities are also considered. Two new species, Brachyopterella ritchiei sp. nov. from Seggholm and Hardieopterus (?) lanarki sp. nov. from the Logan Water are described. Stylonurella spinipes (Page) is redescribed and this species is reported for the first time from Seggholm.

The new information provided by this study has raised a number of problems of classification and the criteria upon which eurypterids are classified, and particularly those applied to the stylonuroid eurypterids, are re-assessed and a new classification of the Stylonuroidea proposed. This has required the description of new taxa; a new family, the Parastylonuridae, is proposed to accommodate Parastylonurus, Hardieopterus and probably Lamontopterus which share a unique combination of characters of the prosomal appendages and metastoma. A new genus, Kiaeropterus, is described to accommodate certain species previously assigned to Stylonurella but displaced from that genus as now emended.

A reconstruction of Parastylonurus ornatus in the walking position is attempted and has resulted in the recognition of a new generation of problems related to the functional morphology of these animals. Criteria which may appropriately be used in deciding the manner in which they walked and the posture which they adopted when doing so, are discussed. It is suggested that, in response to certain anatomical and physiological constraints which otherwise would have rendered the animals unstable in the walking position, the post-abdomen and telson have been specialised as hydrodynamic structures for monitoring water movements and vectoring the animal for maximum walking efficiency. The significance of this hypothesis is discussed in relation to the functional morphology and evolution of other members of the Stylonuroidea.

The term ‘monchiquite’ has suffered such conflicting usage that a redefinition is here proposed: monchiquites are alkaline lamprophyres with essential brown amphibole and/or biotite but not necessarily with olivine, possessing a near-isotropic feldspar-free base of glass (hyalomonchiquites), analcime (analcime-monchiquites) or nepheline (nepheline-monchiquites). This effectively reverts to Rosenbusch's original definition, whilst accommodating established practices in the subsequent literature. Notwithstanding certain published interpretations, the type monchiquites from Monchique and Rio de Janeiro are hyalomonchiquites.

The Monchique monchiquites are associated with camptonites and sannaites in a dyke swarm invading the Monchique foyaitic intrusion. Field, petrological, geothermometric and geochemical evidence is presented to suggest that these dykes resulted from two mixing processes: (i) a version of Bowen's classic reaction between mafic crystals and alkaline liquids—here between cumulus divines and foyaitic magma; (ii) hybridisation of hydrous theralitic and nepheline syenite magmas, restricted by liquid immiscibility. The secondary origin of certain dykes is evinced by extreme mineralogical disequilibrium. The monchiquites could represent a more advanced stage of such processes than the camptonites and sannaites.

A method of conducting a resistivity sounding, up to a maximum spacing of 5 kilometres, is described. By conducting measurements, in a symmetrical fashion, about the sounding centre and in two perpendicular directions, it is possible to obtain results which are relatively insensitive to the orientation of the electrode array used and entirely related to the local area around the sounding centre. By choice of the progression of spacing used, it is also possible to express the results in terms of resistivity measures suitable for subsequent interpretation.

A resistivity sounding curve, conducted in this manner at Rookhope, shows the existence a highly resistive basement at interpreted depths which are in reasonable accord with the known depth to the Weardale granite in this area.