The reverse aspect of a proximal end of I. manubriatus is described and its relation to the mode of development of some early biserial forms is briefly discussed. Two new names descriptive of types of development are proposed.

Outcrops of Carboniferous Limestone were examined along the coast of North Wales around Penmon in Anglesey, and Great Orme's Head, Gloddaeth and Llanddulas in Caernarvonshire and Denbighshire.

Tectonic forces have folded, jointed and faulted the Limestone, but each area has reacted differently. The differences are discussed and the effects on the different limestone units illustrated.

Caledonian structures adjacent to the areas are briefly discussed. Variation in fold strike from north to east or south-east in the Carboniferous rocks is a reflection of the change in strike in the Lower Palaeozoic rocks, as is the northwest to north strike of the faults.

It is postulated that folding and faulting of the Carboniferous Limestone areas during the Hercynian orogeny was totally guided by Pre-Cambrian and Caledonian structural trends in Anglesey and on the mainland coast, and that the southern compression during the orogeny only accentuated pre-existing trends.

Various views have been expressed about the origin of the Red Sea Depression. Many earth scientists favour large-scale crustal separation and rotation of Arabia with respect to Africa—the paar theory; whereas a minority believe in a simple tensional origin. In the writer's view the almost “timeless” models presented by Drake & Girdler (1964) and Laughton (1966) are unacceptable because little of the available stratigraphic, structural and geo-morphological data was utilized in their construction. A tension system may have existed in the Red Sea area in late Pre-Cambrian and early Palaeozoic times. A depression existed in the northern part of the region in Carboniferous times and during Cretaceous times a tongue of Tethys occupied the northern and central portions of the depression. In Miocene times an extensive evaporite basin developed occupying most of the depression. The sill was situated in the Gulf of Suez Ayun Musa area.

The main and central troughs developed as a result of tension in Pliocene and later times. The Gulf of Aqaba Depression was formed by a fault system continuous with Dead Sea System which originated in (?) early Cretaceous times. The northern and central parts of the gulf were invaded by the sea in Pleistocene times.

The escarpments which bound the Red Sea Depression are in very few places fault or fault line scarps. Primarily they appear to be erosional features developed by pediplanation across the downwarped margins of the depression. In places, the shoulders and flanks were faulted later. In this way the uncon-formable nature of the contact, between the Mesozoic-Tertiary sediments and the Basement Complex (mainly Pre-Cambrian) which occurs at the foot of the escarpments, is best explained.

The usage and synonymity of the names of some olivine-bearing feldspathoidal extrusive rocks is discussed. In the nephelinic rocks it is suggested that the terms nepheline-basalt and olivine-nemafite be abandoned, and that the use of olivine-nephelinite be continued. A similar recommendation is made for other feldspathoidal rocks.

The type specimen, other figured specimens and supplementary material of Monograptus tenuis (Portlock, 1843) have revealed the presence of pronounced ventral apertural processes which place this species in a unique position in the Monograptina. The affinities of M. tenuis are discussed.

Gravity readings were taken on a 40-km traverse running roughly NE-SW across the Liruei Younger Granite ring complex of Nigeria. A negative Bouguer gravity anomaly of about 16 milligals amplitude was observed over the complex.

Electronic computing methods were used in the interpretation to obtain the best 2-dimensional and 3-dimensional structures which would fit the observed anomaly. The best computed models indicate that the contacts between the Liruei Complex and the surrounding Basement Complex dip outwards from the ring complex and, based on the surface density contrast of 0·10 gm/cc, the depth to the base of the density contrast is of the order of 7,500 metres.

The thecal form of Monograptus argutus Lapworth and M. leptotheca Lapworth is similar to that of M. incommodus Törnquist, the type species of Pribylograptus Obut & Sobolevskaya; their thecae are geniculate and have introverted and laterally expanded apertures, and M. leptotheca has in addition apertural hoods. The relationships of these species are discussed.

Some basaltic and andesitic rocks from the Tweed Shield Volcano are tholeiitic in character as evidenced by their chemistry and the nature of their pyroxenes inferred from optical data. A common mineral assemblage in the more basic members is olivine-clinopyroxene-plagioclase-opaques-(glass). Petrographic criteria that characterize tholeiites are often lacking, and some of the more basic lavas appear to link the more typical tholeiites with transitional olivine basalts. Many of the Tweed volcanic rocks are more potassic than similar rocks in other tholeiitic sequences. The likelihood of differing lineages in the shield area is noted.

The system of stratigraphic classification used by field geologists working in Africa is briefly reviewed and a hierarchy of terms is suggested, taking into account the requirements of those interested in local field problems and those concerned with the tectonics and composition of the African continent as a whole. On the local scale, rock units are best named according to the lithostratigraphic classification. On a regional scale, the criteria for defining rock units are essentially tectonostratigraphic and two new terms for them, in ascending order of magnitude, Orogenic Assemblage and Orogenic Complex, are proposed. The two schemes are united through the Sequence, which can contain any number of lithostratigraphic units of any order of magnitude.