The Ordovician Fauna from the Contaya Formation from the lowlands of eastern Peru is fully described for the first time. The fauna is restricted and consists essentially of brachiopods, trilobites and Graptolites and three new species, the brachiopod Tissintia simplex, and the trilobites Anebolithus tafuri and Porterfieldia contayaensis are described. The fauna is shown to have close affinities with those of central Europe and North Africa.

In the last few years the problem of the lower boundary of the Cambrian has been dealt with in dozens of works which considered not only the history of the question but all the current material available. It is a subject discussed at many national and international symposia. Although great progress has been achieved in drawing together the points of view on the position of the boundary (compare the results of the symposia held in Paris in 1958 with that in 1974), the range of different opinions still remains wide, particularly with regard to the zonal scales (for example, in Siberia, from the base of the Nemakit–Daldyn horizon up to the base of the beds with Fallotaspis). First, therefore, we give consideration to those questions which often constitute a stumbling block. It seems necessary to make a reservation that some of the difficulties arising may undoubtedly be referred to as purely psychological.

A brief review of Becke's (1908) replacement and Schwantke's (1909) exsolution models for myrmekite genesis and further consideration of the morphology and spatial distribution of myrmekite as outlined by Phillips (1974) lead to the conclusion that both hypotheses have a place in explaining the origin of myrmekite. The Schwantke model is generallybest applied, for example, to high-level undeformed massive granitoids and the Becke model to deformed metamorphic rocks. The latter hypothesis and a third model involving interaction between exsolution and replacement (Ashworth, 1972) may be used especially to explain the association of muscovite and myrmekite in rocks whose mineral assemblages have undergone retrograde modification, involving either redistribution of Na, Ca and K by local metasomatic reactions among the mineral grains, or metasomatic change of bulk rock composition.

New work on the sedimentology and palaeontology of the classic area of the ‘basinal’ facies of the Carboniferous Limestone requires that a formal lithostratigraphic framework be established to rationalize the existing system of local rock units and regional lithofaunal ‘groups’ and ‘series’. Five formations, based on the existing ’groups‘ in the Clitheroe area, are defined for the whole Craven Basin outcrop. They are, from the base, the Chatburn Limestone Formation, the Clitheroe Limestone Formation (which includes the ’reef-knolls’ of the Clitheroe area), the Worston Shale Formation, the Pendleside Limestone Formation (to include the knolls of the Craven reef belt) and the Bowland Shale Formation. The chronostratigraphy, in terms of the six British Dinantian Stages, and a provisional micropalaeontological biostratigraphy are outlined.

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.

The Ordovician pterygometopid subfamily Chasmopinae is considered to include not only Chasmops McCoy, 1849, and Uralops Ancigin, 1970, but also a number of other genera which encompass species previously referred to Chasmops. These are: Toxochasmops McNamara, 1979; Scopelochasmops gen.nov.; Bolbochasmops gen.nov.; and Rollmops gen.nov. A close correlation is shown to exist between distribution of chasmopines and lithofacies, which indicates habitation in ashallow water environment. A westerly spread of chasmopine species at various times from eastern Baltoscandia is considered to correspond with a similar spread of the shallow water environment. This is shown by the periodic appearance of members of the subfamily in the Oslo region and Britain. Thereis a general reduction in number of chasmopine species and genera away fromthe eastern Baltic.

The Maumtrasna Formation is a thick succession of coarse clastic rocks situated in the South Mayo Trough of western Ireland. Its upperage limit is not defined but it is post-Llanvirn in age and probably Ordovician. Several aspects of the conglomerates within the succession are compatible with the action of a glacial influence during its deposition. New evidence is presented which tends to confirm the glacial hypothesis. 10.7% of garnets separated from the matrix of the conglomerates exhibit chattermark trails. Published accounts of such trails indicate that they are only found in sediments which are glaciogenic or were derived from pre-existing glaciogenic sediments. It is suggested that the Ordovician glacial activity in the South Mayo Trough took the form of a highland glaciation which was maintained, possibly at sub-equatorial latitudes, by a continuous uplift of the source area.