Recently acquired deep seismic reflection profiles recorded to 12 s two-way travel time in southern Britain suggest that the crust beneath this area is commonly divisible, vertically, into three zones.These zones, based upon seismic character, can be related to structural or tectonic units. They comprise an upper zone of cover rocks of various ages, a middle zone of folded and thrust rocks, and a lower zone tentatively identified as metamorphic or crystalline basement. A sketch crustal profile from Dorset to Yorkshire summarizes the data and illustrates the distribution of the zones.

Well-preserved, silicified Obruchevella from the earliest Cambrian (Meishucun Stage) sequence from Meishucun section in Yunnan Province, China contains distinct cross-partitioning. This suggests that this helically coiled microfossil represents the remains of an oscillatorialean cyanophyta. Obruchevella is a microfossil that exhibits a variety of form that may be produced through degradation. Obruchevella identified in the Meishucun section includes O: parva, O. parvissima, O. delicata, O. meishucunensis and several other morphs which are yet to be identified.

Relic pillows in the middle Proterozoic amphibolites, occurring in the Sirohi Road–Abu Road tract of Rajasthan, India exhibit contrasted mineral assemblages from core to rim – mimetic after the crystalline core, the zone of incipient crystallization, and the rim of the original pillows. The major element distribution pattern across the pillows indicates exchange of Na–Al for Ca (Mg, Fe) in an inner reaction zone, surrounding the core and in the inner margin of the rim, and Fe–Al exchange for Ca–Si at the outer margin of the rim.

Despite such exchanges around the rims, these pillows have retained their initial geochemical characteristics internally and thus have largely acted as closed systems during post-emplacement metamorphism. Mineral parageneses indicate that the contrasted mineral assemblages could evolve from domainal characters of the co-existing fluids, the compositions of which were only buffered by the reacting minerals during regional metamorphism.

The major, minor and trace element contents of the pillows and of amphibolites of diverse petrographic character in the region further establish that the pillow interiors and the massive amphibolites were least modified during metamorphism(s), and represent oceanic tholeiites. Their average 2300 ppm K, 4.5 ppm Rb, 150 ppm Sr, along with the K/Rb and K/Sr ratios of 510 and 15 respectively resemble that of the low K-tholeiites, occurring nearest to the trenches in modern island arcs. On the other hand, the higher values of 17300 ppm K, 4.9 ppm Rb, and 210 ppm Sr of the banded and the schistose amphibolites indicate that they were contaminated in various magnitudes by oceanic sediments.

The appearance of the first abundant skeletal organisms in the earliest Cambrian was a quantum leap in the evolutionary history of life. It provided the foundations of the animal kingdom from Cambrian times onwards. This paper demonstrates that this evolutionary process resulted from a combination of environmental and biological factors. The author maintains that the appearance of the oldest shelly fossils is a reasonable criterion for defining the Precambrian–Cambrian boundary. This arises not only from the viewpoint of taking the Cambrian Period as the first period in the Palaeozoic Era, but is also a logical extension of regarding the history of life as being divisible into a series of developmental stages.

An understanding of the response of migmatites to deformation is crucial to an interpretation of their structures, and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts. In partially molten systems containing more than 30% melt the classical theories of fold formation are inapplicable; the folds produced are of the ‘viscous fold’ type. Their geometry is unpredictable and may mimic structures due to refolding; this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins. Failure to distinguish ‘viscous folds’ from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area, and to consequent misinterpretation of the true structural relations between geometrically complex high-grade and more regularly deformed low-grade areas.

Arumberia is a large impression fossil which may be allied to the Ediacaran fossils Ernietta and Pteridinium. New finds and published evidence suggest that it was restricted to very shallow, possibly non-marine, environments, and to rocks of latest Precambrian to Lower Cambrian age. Well-preserved material from the Longmyndian shows that it was associated with numerous small spherical structures. At present it is only of broad stratigraphic use, but as the wide range of characters observed becomes better understood it may prove more valuable, especially as it occurs in otherwise poorly fossiliferous environments.

Four sedimentary sections seen in continuous exposures along the Lena River on the Siberian Platform in Yakutia contain a record of the geomagnetic field during the Tommotian and Atdabanian stages of Early Cambrian time. The direction of the stable remanent magnetization indicates that the Siberian platform was located on the equator, and the corresponding palaeomagnetic pole provides a well-dated extension of the Siberian apparent polar wander path. A belt of archaeocyathid bioherms which separates two major facies zones in the lower Cambrian was positioned on and aligned more or less parallel with the palaeoequator. The geographical position of this belt appears to have tracked the southward motion of the Siberian platform during post-Tommotian time. These palaeomagnetic results combined with the extensive biostratigraphy of the Siberian Platform provide a provisional geomagnetic polarity time scale for this part of Early Cambrian time. Comparison of these results with data of similar age from Central Australia suggests that strata of Tommotian and lower Atdabanian age are not present in the Amadeus Basin of Australia.

The transitional interval between the Adelaidean and Ediacaran systems in the central Flinders Ranges, South Australia, comprises mainly basinal sediments, with some tuff beds (Bunyeroo Formation) and a widespread thin dolomite bed which apparently evidences a brief regressive episode (base of Wonoka Formation). Body imprints of metazoans, trace fossils and probable faecal pellets are present at various levels in the Ediacaran succession. Comparable assemblages occurring in key successions in southern Africa, northern Russia, Siberia, Newfoundland and England promise a global biostratigraphy. One Ediacaran body fossil occurs in the Yangtze Gorges section, China. Analysis of abundant late Precambrian radiometric data for the present North Atlantic margins suggests that the Ediacaran may be dated between about 590 Ma and ~ 545–540 Ma.

Two Carboniferous trilobites, Ditomopyge convexa sp.nov. and Paladin (Paladin) sp.ind., are described from the Nordenskiöldbreen Formation in Spitsbergen. The new material is of considerable interest as it extends the known distribution of Carboniferous trilobites and provides further information on palaeobiogeography.

The colours of conodont elements recovered from Silurian limestones in the Oslo region, Norway, range from brown to grey. Samples from the south of the region contain black and grey conodonts, indicative of high palaeotemperatures. There is a general decrease in thermal metamorphism towards the north, with the lowest palaeotemperatures recorded from Toten, Ringsaker and parts of the Ringerike district. There is a close correlation between thermal metamorphism and the proximity of Permian intrusions.

Select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the South East Indian Ocean Manganese Field indicate that this is composed of a random stratification of crystallites of vernadite MnO2. (R2O, RO, R2O3)x. yH2O, where R represents elements such as K, Ba, Na, Ca, Mg, and a disordered hydrated iron oxide, possibly ferrihydrite 5Fe2, O3. 9H2O or feroxyhyte δ′-FeOOH. Whether the dark component is an irregular mixed-layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain.

Calcareous algae make their first appearance near the base of the Tommotian. The oldest confirmed occurrences are of ?Gemma, Obruchevella and Renalcis in the Nemakit-Daldyn Horizon and late Yudomian of Siberia. A little higher in the sequence, in the Aldanocyathus sunnaginicus Zone of the earliest Tommotian, Angulocellularia, Bajanophyton, Batenevia, Botomaella, Girvanella, Hedstroemia, Korilophyton, Proaulopora, Subtifloria, and Tarthinia appear. Immediately above this, in the Dokidocyathus regularis Zone of the middle Tommotian, Chabakovia appears with the epiphytacean genera Epiphyton, Gordonophyton and Tubomorphophyton. There are only minor subsequent additions to this flora before the end of the Atdabanian. Kordephyton appears in the Dokidocyathus lenaicus Zone of the late Tommotian and Razumovskia in the early Atdabanian.

These fossils constitute three calcareous algae assemblages (CAA 1, 2, 3) characteristic of the Nemakit-Daldyn Horizon/late Yudomian, early Tommotian, and middle Tommotian/Atdabanian respectively. Most of the genera are long-ranging, but their rapid appearance and diversification near the base of the Tommotian repesents an important event in the history of calcareous algae and augments faunal data concerning evolution and biostratigraphy near the Precambrian/Cambrian boundary.

Upward-thinning stellate and polygonal carbonate structures are described and compared to modern and ancient stromatolites. Although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential. The preservation of these from the Stoer Group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction. Associated limestones with some similar features are interpreted as flat to mamillated microbial mats.

The chronic repetition of a small graphical error, initiated by H. B. Woodward and depicting the Birchi Beds (Lower Jurassic) dipping beneath Lyme Regis, needs rectifying since, by implication, it leads to a gross stratigraphical and structural error amounting to about 21 m (70 ft) at Lyme Regis, Dorset.