All trilobites known from the lower and upper Balclatchie and lower Ardwell groups of the Girvan district are listed and frequencies recorded. Eight new species are described, a number of generic assignments are new, and hitherto undescribed parts are illustrated. Of the 60 named species, 19 occur in the lower and upper Balclatchie and lower Ardwell groups; the upper Balclatchie Group yields the largest number of species. The assemblage is generally indicative of outer shelf conditions of deposition; a deeper water association at certain Balclatchie Group localities consists of 5 species identical with, or closely related to, species from the Liberty Hall facies of the lower Edinburg Formation of Virginia, U.S.A. This deeper water element constitutes a significantly larger proportion of the trilobite assemblages at certain localities than it does at others. A further 8 species from the Balclatchie Group are allied to lower Edinburg Formation forms, thus confirming the evidence of the brachiopods regarding the strong North American affinities of the fauna. The Balclatchie conglomerate is considered to be the result of a catastrophic event accompanied by slumping near the shelf edge causing the instantaneous entombment of the fauna.

All trilobites known from the Ardwell Group, Craighead Inlier, Girvan district are listed and frequencies recorded. Encrinuroides lapworthi n. sp. from the Sericoidea Mudstones, and Bumastoides fornax n. sp. from the Kiln Mudstones, are described. The Sericoidea Mudstones constitute a deeper water interlude in the complex succession which comprises the Craighead Limestone Formation; graptolites from this horizon indicate low Dicranograptus clingani zone. The closest resemblance of the trilobite assemblage as a whole is to faunas of Trenton age in North America. The occurrence of forms allied to Boda Limestone (Ashgill) species suggests that these are long-ranging, carbonate associated, trilobite stocks.

Metamorphosed abyssal ocean-floor tholeiitiic rocks, little affected by crustal contamination and probably formed at a spreading ridge, occur as a dyke complex in banded gabbros with oceanic affinities and as small tectonic lenses in serpentinised peridotite. Igneous textures and mineral assemblages have been partly or completely replaced in both dykes and gabbros. Metamorphic development of clinopyroxene and very Ti-rich hornblende at 900-1000°C was followed by a low temperature actinolite-chlorite assemblage and then by pectolite-bearing veins. Geochemical variations resulting from magmatic and metasomatic processes have been distinguished and plots of major and trace elements used to establish tectonic environment. The very high temperature metamorphic mineral growth associated with beerbachite formation indicates that the dyke rocks were in a high heat-flow environment for a considerable time, presumably in the vicinity of a spreading ridge. Obduction of a very hot slab of oceanic lithosphere accounts for the superimposed mineral assemblages.

Spatially associated pillow lavas have been affected by crustal contamination and are not comagmatic with the dykes. There are petrochemical characters indicating that some of the lavas are ocean-floor basalts. For other lavas, features suggesting emplacement in a continental or an island-arc environment could also be consistent with development in a marginal basin. However, there is so much variation in composition of pillows from margin to centre, from small to large and from metasomatic activity, that their compositional fields cannot be used for discrimination of basaltic type with the same confidence as for the dykes. Accordingly, it is suggested that the petrochemistry of sheeted dyke complexes, rather than of pillow lavas, be used for this purpose in the study of ophiolites.

Cell culture systems have been developed to assess the potential pathogenicity of mineral dusts. The in vitro cytotoxicities of a variety of dusts towards mouse peritoneal macrophages, Chinese hamster lung cells (V79 cell line) and human alveolar type II cells (A549 cell line) were investigated.

Non-pathogenic dusts were found to be inert in vitro. Fibrogenic non-fibrous dusts such as silica were only cytotoxic towards macrophages. Fibrous dusts which are both fibrogenic and carcinogenic in vivo are cytotoxic towards all three cell types, their cytotoxicity being dependent on fibre size. The size range important for the observed biological effect is longer than about 8 μm and thinner than about 1·5 μm.