Techniques are described for the preparation of flexible casts of macrofossils preserved as natural moulds. Materials are discussed and the choice of two high-cost silicone rubbers justified.

Chemically similar altered gabbro, tholeiitic basalt, basaltic andesite and calc-alkaline rhyolite of Early Miocene age is present on Small Nggela, Solomon Islands. Large vesicles are invariably lacking from the autochthonous basaltic pillow lava which has narrow chilled margins, but clasts of allochthonous basalt present in coeval Early Miocene sediment are commonly vesicular. This suggests that the autochthonous lava was deposited in deep water (> 2.5 km) whereas the allochthonous lava was formed upslope in shallow water. A progressive increase in the tholeiite in Zr, Ti, K2O/(K2O+Na2O), Rb/Sr and K2O/Rb from N to S confirms that an Early Miocene southward-descending subduction zone, postulated by some authors, was present. Its recognition implies that the subduction zone did not migrate far during the Early Miocene.

The classification of the genera Plaesiacomia Hawle & Corda, 1847, Kerfornella Henry, 1976, Colpocoryphe Novák in Perner, 1918, Salterocoryphe Hammann, 1977 and Neseuretus Hicks, 1873, is discussed. Plaesiacomia and Kerfornella are attributed to the Homalonotidae (sub family Kerfornellinae nov.), while Colpocoryphe, Salterocoryphe, and Neseuretus are regarded as belonging to the Calymenidae. The author's opinion is mainly based on the morphology and evolution of the coaptative devices, and on the morphology of the hypostoma.

This study of Silurian volcanism considers three small intrusions near Bishop's Castle, Salop, as possible volcanic feeders. Acid magma intrusive into Silurian calcareous siltstones has resulted in microgranite dykes, hornsfelsed country rock and metasomatized breccia. The intrusions are of late Wenlock age or younger, but they are relatable to other Wenlock igneous rocks in the area, and are in contrast to nearby Carboniferous basaltic rocks.

Load-cast structures in the Caledonian, synorogenic, Fongen-Hyllingen layered basic complex closely resemble those deformations resulting from reverse density stratification in experimentally studied, water-saturated sediments. The mushroom-shaped structures are apparently restricted to a single horizon within an interlayered, metamorphosed, dunite–troctolite sequence. They generally have a symmetrical form, revealing a polygonal pattern in the plane of the layering. The density contrast between an olivine-rich crystal mush overlying a plagioclase-rich crystal mush, both very close to the igneous sediment–magma interface, is believed to have caused the deformation. Subsequent consolidation occurred by adcumulus growth.

Box-fault systems are striking arrangements of short faults that are associated with complex groups of elongate, tilted fault blocks (ramps). They occur within the faulted eastern shoulder of the Rift Valley, close to the equatorial bend in its alignment. This association of small-scale structures is shown to be integrated within the large-scale, asymmetrical structural pattern of the equatorial bend.

A total of 111 major element analyses have been made of impure calcareous rocks from the Late Precambrian Moinian sequence in NW Scotland. Samples were collected along a 36 km traverse from three stratigraphic horizons which are repeated by folding and vary in metamorphic grade from lower to upper amphibolite facies. Anorthite content of the plagioclase, which increases progressively from albite to anorthite, was assessed by X-ray diffraction measurement of 2θ (131–11); this value is used as a ‘metamorphic index’ for rocks with a CaO/Al2O3 (wt. %) ration of 0.3–0.7 and Na2O/Al2O3, < 0.35. Na2O/Al2O3 and K2O/Al2O3 ratios plotted against this index, together with the spatial relationship between metamorphic/chemical isograds and stratigraphic boundaries show that both Na (0.24–4.82% Na2O) and K (0.01–3.28% K2O) are lost from the calc-silicate rocks during prograde metamorphism. These chemical changes result in a variation of the stable mineralogy with increasing metamorphic grade and take place through the medium of the intergranular fluid.

At present one is not able to devise a single, standard classification of igneous rocks that is acceptable to all petrologists. This is mainly because igneous petrology consists of an uneasy union between the descriptive science of petrography and the explanatory science of petrogenesis, and at present the latter discipline is unable to provide a coherent model, or series of models, that can account for the origin and evolution ofall igneous rocks. Some of the more significant concepts used in the classification of volcanic rocks are examined, and three separate, yet complementary, classifications are presented.

The incidence of volcanic pebbles in the gravels of the middle Thames basin is noted. The detailed petrography of volcanic clasts at two sites is described and found to be broadly similar to that of material from sites in East Anglia, thought to be of Welsh origin. The frequency of volcanic pebbles in the two areas is also similar. This evidence suggests that volcanic material was brought into East Anglia via the ancestral Thames.Records of volcanic rocks in the drift deposits of the upper Thames basin provide additional evidence of this route.

In the British Tertiary intrusive centres emplacement of cone-sheets, ring-dykes and related magmatic bodies followed in shape and sequence the pattern of Hertzian fracture produced in the country rock by the magmatic diapir. In Ardnamurchan doming of the country rock, conic fracture and intrusion of cone-sheets started the development of the intrusive centre. Following that, pressure was reduced and strain relaxation occurred which resulted in arcuate and median fractures. These fractures were later on intruded by magma, hence ring-dykes (curved flanges) were formed. Resumption of pressure initiated the second cycle of cone fractures (and inner cone-sheets of centre 2).

A geomagnetic survey indicates that the Carboniferous igneous rocks in the Tickenham area are more extensive than previously recognized. Inversions of the magnetic anomalies suggest the causative basaltic body is tabular in form, conforms to the regional dip and has a coplanar magnetization. The magnetization vector orientation indicates emplacement during a period of magnetic field reversal and thus at a time different from other Carboniferous igneous rocks in the region.

Fracture propagation in the crust under post-critical conditions (rapid propagation), and possibly in some instances even under sub-critical conditions (slow propagation) can produce fracture-branching in a single continuous process. Later local or regional stresses result in displacements along the fractures and secondary faulting develops. This concept can explain various secondary features like conditions of branching, branching-angle and shallow secondary faults. The splaying of the Hope Fault in New Zealand is primarily a result of early fracture bifurcation and later minor displacements.

Recent ideas on evolution in the graptolites have been based upon an assumption either of passive flotation and passive feeding, or of active and co-ordinated ciliary feeding resulting in automobility. These ideas are compared and a possible evolutionary consequence of automobility is suggested.

The Newania carbonatite is mainly ferruginous rauhaugite with subordinate ankeritic carbonatite and dykelets of sovite. In a zone of fenitization the surrounding granite-gneiss country rock has been converted into syenitic fenite, composed mainly of feldspar and ferri-eckermannite with small amounts of albite, anorthoclase and accessory apatite.

The metaprotaspid of the bumastine Failleana calva is similar to protaspids of scutelluids, whilst late meraspids and early holaspids of F. calva are similar to fully mature styginids. This suggests that the bumastines were derived from the styginids in the Early Ordovician and that the bumastines later gave rise to the scutelluids. Bumastus and similar Silurian trilobites are phyletic derivatives of Ordovician bumastines and not effaced scutelluids as claimed recently by Lane & Thomas. Revised diagnoses of Illaeninae and Bumastinae are presented.

A unique columnar sandstone, produced by the thermal metamorphism of an Upper Old Red quartz arenite, is described, from South Bute, together with other examples of similarly altered sediments from nature and industry. The columnar structure probably developed as a result of the emplacement of a basic dyke via a fissure. In view of the relatively large area exhibiting this structure, metamorphic effects must have been amplified by the agency of steam and volatile constituents of the magma, passing up through the fissure.

Examination of the Eichstätt specimen of Archaeopteryx shows that the pubis agrees with those of the Berlin and London specimens in indicating a downward and backward inclination of some 135° relative to a line drawn through the lower extremities of the iliac blade. The greater part of the backward rotation of the bird pubis had thus taken place by the Kimmeridgian Stage (sensu anglico) of the Upper Jurassic. A definite pectineal process is present in Archaeopteryx, indicating the existence of a well-developed ambiens muscle. Some preliminary remarks are made about the skull of Archaeopteryx.