A series of dioritic, granodioritic and granitic igneous rocks, of Pre-Cambrian age, is exposed near Johnston in south Pembrokeshire. Chemical analyses of representative rocks show the suite to be of calcalkaline type. An origin is suggested involving magmatic differentiation of a diorite parent magma, and the granitic rocks are compared with a granophyre of similar composition in north Pembrokeshire.

A specimen from the Krosno Beds (Oligocene) of the Polish Carpathians shows irregular scour casts, in the shallower parts of which terracing is horizontal but in the deeper parts of which it is dipping at up to 27°. It is inferred the the original sea floor consisted of cross-laminated surface layers. The palaeocurrent significance of inclined terraces is discussed.

The brachiopod Orthisocrania divaricata (M'Coy) is generally considered to be a fairly long-ranging form occurring in both the Caradoc and Ashgill Series. The latter age is based principally on records of its common occurrence from the Chair of Kildare, Ireland, but the species is not present in the Ashgill beds at this locality. It does occur there, however, in association with a fauna whose age is here judged to be Longvillian on the basis of its strong similarities to that of the Gelli-grin Calcareous Ashes. Examination of other records and occurrences suggests that this inarticulate is restricted to the Longvillian in the British Isles, and is therefore of some importance stratigraphically.

The Phuket Group is the oldest rock unit in the Phuket-Takua Pa-Krabi region of the Thai Peninsula. The Group comprises two Formations: a Lower Formation of Ordovician, or possibly Cambrian, to Lower Permian age, exceeding 3 km in thickness, and an Upper Formation of early Permian age between 100 and 200m thick.

Facies analysis shows that the Lower Formation consists of mass flow deposits and sandstones comparable to the deposits of modern continental rises and continental slopes. The Upper Formation was deposited in a shallow marine and probably deltaic environment. The Phuket Group and litho-logically similar sedimentary rocks to the north and south occupy an elongate belt extending from the Shan States of Burma to the Langkawi Islands in Malaysia. The sediments, which are rich in quartz, were derived from a continental area and deposited on its margin. In contrast to previous interpretations of the Palaeozoic history of Peninsular Thailand, it is considered that the continental source lay to the east. The continental margin resembled modern margins of either Atlantic or Japan Sea type.

This work describes the Wenlock sedimentary sequences south of Killary Harbour where the fullest successions in north-west Galway are exposed; much of the Upper Silurian in the east (Joyces Country) has been removed by erosion.

The Wenlock beds (the Upper Owenduff and Killary Harbour Groups) rest on shallow marine and continental sediments (the Lower Owenduff Group) of Upper Llandovery (C5–6) age. Conglomerates near the base of the Wenlock are followed by 1,500 m of sandstones, which are mostly turbidites and which contain Middle Wenlock graptolites. These basin deposits are succeeded by a transitional sequence of rise, slope and shelf clastics, also of Middle Wenlock age. The youngest Silurian beds exposed are 800 m of red lagoonal deposits with Lingula.

During Wenlock times, the sediment supply to north-west Galway was mainly from the north and north-west. This observation fits well with the regional picture which places Galway near the north-west margin of a Silurian basin which extended eastwards across Ireland.

The Jimberlana Norite Intrusion, situated near Norseman, Western Australia, is the first real analogue of the Great Dyke of Rhodesia to be discovered. The intrusion has the external form of a dyke, extends for at least 180 km (112 miles), has a maximum width of 2.5 km (1.5 miles), and follows the general easterly trend of the other members of the Widgiemooltha Dyke Suite, all of which have so far revealed characteristics of true dykes. It has a very steep funnel-shaped cross-section, like the Great Dyke, and shows many internal, canoe-shaped complexes along its length, consisting of cumulate ultramafic and basic rocks together with minor acid differentiates. The ultramafic and basic rocks display phase, rhythmic and cryptic layering. The differentiation sequence from ultrabasic to basic rocks is repeated more than once, and therehave clearly been several pulses of magma up the tensional opening. This is confirmed by the recognition of at least two magmatic unconformities. The broader petrogenetic questions posed by this unusual intrusion are discussed.

An index of weathering for silicate rocks is proposed, based on the proportions of the alkali and alkaline earth metals present. These are considered to be the most mobile of the major elements. The bond strengths of the elements with oxygen are used as weighting factors in the index, which measures both the degree to which a rock has already been weathered with respect to the parent material, and also its susceptibility to further weathering.

A lateral cryptic variation is recognized in layered ultramafic rocks of the Hartley Complex, the largest of the four lopoliths that constitute the Great Dyke. Over a lateral distance of some 120 km, the En content of orthopyroxene from thick, continuous bronzitite layers is up to 6% less at the southern extremity of the Complex than in the central area. This is interpreted to be a result of more rapidly falling temperatures in a thinner body of basic magma that gave rise to a condensed sequence in marginal areas of the lopolith compared to the central area.

Following a well-marked period of addition of parental basic magma which appears to have had the incidental effect of linking up the four lopoliths, this compositional relationship in composition is reversed, i.e. the orthopyroxene from the base of an upper bronzitite layer of the southern marginal area of the Hartley Complex is more magnesian than that from the equivalent level in the central area. This is interpreted to arise from the proportion of fresh added magma to previously emplaced and partly crystallized magma being relatively greater in the marginal area than in the central area of the lopolith.

When basalt lava flows from air into water it leaves a distinctive record of the waterlevel of the time in the form of lava sheets overlying and passing down into vitric breccia and/or pillow lava. Relative movements of waterlevel and a volcanic pile or terrain over a period of time may be readily deciphered from such records.

Two cleavages occur in the sandstones: coarse fissuring, and a fine irregular fracturing, which may form conjugate sets. Linear structures of five styles, all of which are parallel to the fold axis, are developed on the bedding due to the intersection of this element by the cleavages.

The argillaceous siltstones of the floodplains contain, on average, 15% of calcium carbonate. This appears to have been precipitated between the detrital grains shortly after their deposition. The siltstones also contain calcium carbonate concretions which formed as the ground water dried out in the upper part of the water table. Bedded marlstones, containing up to 68% of carbonate in the lakes appears to have been stimulated by Charophyte algae. The marlstones include dolomite in some parts of the Formation. The channel-fill deposits include carbonate detritus from the source areas, and from reworking of Wood Bay Formation sediments. They are frequently cemented by calcite.

The regional pattern of carbonate derivation, transportation and deposition is summarized.

Study of the punctation mosaics of Moorellina granulosa (Moore) and Moorellina ornata (Davidson), revealed by serial sectioning and stereoscan photomicrographs, shows that the apparent random distribution of punctae may be reconciled to two superimposed regular insertion patterns. Careful plotting of the endopunctae of M. granulosa from serial, cellulose acetate peels, reveals the presence of impersistent punctae. A new model is proposed, based on superimposed insertion patterns and offering an explanation for impersistence of punctae.

The paper represents a reassessment of the drift stratigraphy at Porth-clais. The characteristics of the various Pleistocene deposits at the site are analysed in detail, and the sequence of drifts is then examined in its regional context. While the age of the raised beach at Porth-clais is still open to doubt, it seems that the non-calcareous till was deposited during a Late Weichselian glaciation by the Irish Sea glacier. This glacier probably extended much further south in St. George's Channel than suggested by other workers, although the ice stream which crossed St. David's Peninsula may not have been very thick.

It is proposed that the term pyrothalassite should be used to describe the materials that form the outer and upper covering of a volcanic edifice that rises from the sea bed, and it includes the fragmental materials produced by hydroexplosions and surf action in the upper layers of the sea. This material is both porous and enriched in thalassophile elements. These two characteristics give a pyrothalassite layer the ability to exert a profound influence on the magmatic evolution of volcanic islands that contain, or contained, such a layer.

The Pre-Cambrian rocks of north-eastern Botswana comprise two major geotectonic domains: the south-western extremity of the Rhodesian craton, and the surrounding mobile belts– namely the Limpopo Mobile Belt to the south and the Shashi Mobile Belt to the west-southwest. The Mosetse-Matsitama area bears affinity to both these environments and this contribution attempts to assess the relationships of the area within the context of the regional geological framework. The area is underlain by a supracrustal schist belt which is interfolded with an infracrustal basement of gneisses and granitic rocks. The schist belt includes metasedimentary and probably metavolcanic rocks of low metamorphic grade and, therefore, contrasts sharply with the rocks of higher metamorphic grade which comprise the basement. Only in the south-west of the belt does a transitional relationship between the two major units occur. Geographical and geological criteria characteristic of both the major geotectonic environments are described, and it is concluded that the area shows a transition from a cratonic to a mobile belt environment. Involvement in a developing mobile belt would initially affect the infracrustal basement, allowing the supracrustal rocks to retain their cratonic characteristics to a more advanced stage.

The biotite selvedges around potash-feldspar rich leucosome material in migmatites originate at phase boundaries between rocks containing hydrothermal and silicate pore-fluids and are thus indicative of incipient anatexis.

Campanile nigeriense sp. nov. is described and figured from the Palaeocene Ewekoro Formation of Western Nigeria. Its juvenile whorls characteristically have four smooth and broad spiral ribs while adult whorls are completely smooth. Vertical ornamentations are lacking. This second record of Campanile from West African Palaeocene strata suggests that the genus may be a stratigraphically useful index fossil in West Africa.

Recent detailed mapping to the north-east of the Harlech Dome in North Wales has produced clear evidence of an early deformation. Thus four distinct deformations can be recognised in the Welsh Caledonides, and their resultant structures are described.

Textural features of two types of garnetiferous biotite-schists from the Iron-ore Series, Gangpur, developed at and near Potob, Ranchi District, indicate stages of development of the two rocks and their polyphase metamorphism.

The Loch Awe Syncline (Bailey, 1913), affecting the Middle and Upper Iltay Dalradian Successions of Argyllshire, is recognised as an F1 structure. The present work shows that the west limb is arched over a pre-O.R.S., late Caledonian monoform responsible for the fan of first cleavage over the area investigated. Reflecting the style of the earlier Ben Lui-Tarbert Monoform (Roberts & Treagus, 1964), the newly described Kilmelford–Turnalt Monoform adds to the symmetry of the Iltay Nappe Complex. “Mushroom” Structure (Rast, 1963).