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.

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.

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.

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.

A study in the deformational patterns of oolites from the Krol Series of the Simla Himalayas has been made in the type area. The deformation in the oolites is the result of the tectonic phenomenon coupled with folding movements during the Himalayan orogeny. The deformation varies with the amount and type of the matrix surrounding the oolites. The angle between the long axis of the ellipse and the principal tectonic extension is smallest in the axial regions of the folds.

A dolomite locality in the Senonian chalk at Mullaghcarton shows a sequence of fabric variations between the unconformity with the Trias and a discontinuity surface marking the top of the basal beds. The four main variations are (1) xenotopic dolomite at the base, (2) hypidiotopic dolomite with zoned crystals and a calcite sealed intercrystalline porosity, (3) zoned dolomite rhombs scattered in a microspar micrite matrix, and at the top (4) micrite with rhombohedral pores. The xenotopic fabric is interpreted as being due to distant source dolomitization and the hypidiotopic fabric with zoned crystals to local source dolomitization. The dedolomitization phenomena are related to the mechanisms of dolomitization; for distant source dolomitization the dedolomitization fabric mimics the dolomite fabric, whereas for local source dolomitization the dedolomite regenerates the pre-dolomitization fabric.

Structures affecting certain bedding planes, and simulating sedimentary ripples, have been found at a number of horizons in the Wenlock and Ludlow rocks of Denbighshire, North Wales. The megascopic appearance of the ripples, including their association with linear structures and their miscroscopical fabric are described in detail; and it is concluded that they are of tectonic origin, being manifestations of bedding-plane slip. The orientations of the ripples and other minor structures suggest that the stress responsible was the regional stress that produced folding, faulting and cleavage.

A new method of contouring polar diagrams using 1% area curvilinear counting cells is described. The method is fast and accurate over the whole area of the stereogram including the periphery and is, therefore, especially suitable for counting weak or diffuse concentrations.

The incommodus, atavus and cyphus monograptid groups appear more or less simultaneously in the atavus Zone. The atavus and cyphus groups are related, one of these probably giving rise to the later tenuis group of monograptids, Possible roots of these groups and relationships with later monograptids are discussed. Monograptus strachani sp. nov. is proposed to replace the name M. incommodus sensu Elles & Wood.

Four stage names are erected within the southern part of the type area of the Llandovery Series, south-east of Llandovery, Carmarthenshire, Wales. They are Rhuddanian, to incorporate the existing Lower Llandovery; Idwian for the Middle Llandovery, and Fronian and Telychian for the Lower and Upper parts of the Upper Llandovery. Correlation with the sequence of graptolite zones is suggested.

The base of the Llandovery at Llandovery is poorly exposed and unfossiliferous, and detailed correlation with other areas may always remain uncertain. Thus the base of the Llandovery Series, and hence the base of the Silurian System, is defined in Lapworth's classic locality at Dobb's Linn, Moffat, Scotland, at the base of the zone of Glyptograptus persculptus.