In the Atikwa Lake area biotite tonalite grades into a peripheral zone of hornblende tonalite as the contact with greenstone wallrock is approached. Greenstone inclusions, common within the hornblende tonalite, exhibit varying degrees of digestion and the host becomes more mafic near many such inclusions. The hornblende tonalite is more heterogeneous than the biotite tonalite, particularly near the contact with greenstone where inclusions are abundant. Modal analyses indicate the presence of large amounts of hornblende near the contact. Spectrographic analyses of composite tonalite samples show that silica decreases while alumina, iron oxide, magnesia, lime, titania, nickel, chromium, and vanadium increase toward the contact. As a whole the data support the conclusion that the peripheral hornblende tonalite is a contamination product which resulted from the assimilation of greenstone by intruding biotite tonalite magma.

Rubidium–strontium and potassium–argon measurements on Lewisian intrusive rocks, considered to be late Scourian in age on general geological grounds, have indeed yielded dates in the range 2450–2600 m.y. This demonstrates that rocks of Scourian age that have escaped substantial Laxfordian reworking are preserved in the Eastern Gneisses of Barra. The relevant geological consequences and correlations are briefly discussed. A cross-cutting late pegmatite yields a typical Laxfordian date of 1679 m.y.

A new structural diagram is proposed that allows simple precise classification of fold orientations. The diagram is also useful for the analysis of the relationship between fold style and orientation.

In addition to the well-established extension, compression and transcurrent relative movements between plates of the lithosphere, this paper considers intermediate or oblique relative movements, namely, transtension and transpression. Transtension is already well established in oblique zones of ocean spreading which consist of stepped transform faults. Transpression is a more complex process. The tectonic consequences of a transpression model are outlined and it is suggested that the tectonic style in Caledonian Spitsbergen provides evidence for this transpression regime as an intermediate stage between compression and transcurrence. It is also suggested that transpression should occur generally and may relate the development of transcurrent faults in orogenic belts.

Cenozoic rocks of north-western Himalayas (excluding the sub-Recent, Recent and Karewa deposits) are represented by the Subathu, Dagshai, Kasauli and Siwalik rocks, which together have a thickness of over 10,000 m and range in age from Upper Palaeocene to Middle Pleistocene. From field and laboratory investigations it is propounded that these sediments, except the Middle and Upper Siwalik, have been derived from low and medium grade metamorphic rocks, acid plutonics and sedimentary rocks of the nearby Himalayan terrains. For the Middle and Upper Siwalik rocks, detritus was supplied by sedimentary and trap rocks as well as by the underlying medium and high grade metamorphic and plutonic rocks. A major part of these sediments has been derived from the rising Himalayas rather than from the Peninsular Shield as believed hitherto. The Subathu rocks were deposited in shallow to moderately deep marine environments; the Dagshai rocks under shallow freshwater conditions; and the Kasauli and Siwalik rocks in a shallow fast-sinking basin. All these sediments accumulated under conditions of rapid erosion, short transportation and rapid deposition.

A study of the Ordovician rocks on the northern side of Abereiddy Bay has revealed that the succession is locally overturned. Consequently the stratigraphic levels of two horizons are reassessed—the Castell Limestone is placed above the Dicranograptus Shale, and the Llanrian Volcanic Series is allocated to the Lower Llanvirnian.

Tillite and other glacial rocks have been found at the base of a sedimentary sequence in the northern part of Tigre Province, Ethiopia. Their glacial origin cannot be doubted, for in addition to beds of tillite containing abundant striated boulders, glaciated bedrock has been found. The rocks are correlatives either of the Upper Carboniferous glacial rocks of southern Africa or of Ordovician glacial rocks recently mapped in the Hoggar District of southern Algeria.

Geological investigations and borehole drilling on the southern margin of the Bovey basin around Mainbow ball clay mine and Ringslade open pit have shown that Devonian slate up to 30 m thick is superimposed on Tertiary sediments. A drag fold beneath the slate indicates that the slate has moved eastwards over the Tertiary material. As the slate is relatively intact and not disaggregated, hillcreep cannot be responsible for the superimposition. A large landslip involving a rotational shear cannot be responsible, as the movement plane dips into the hill over too large an area. The southern margin of the Bovey basin is therefore interpreted as a thrust fault of Tertiary age, with thrust plane dipping 10° to 30° S. It is suggested that this is a rejuvenation of the Variscan thrust recognized in the Bickington area and further west in the Holne area and that the movement on the Tertiary thrust is related to the dextral wrench movement on the Sticklepath fault.