Moinian and Dalradian metamorphic rocks occur in the north-east extension of the Ox Mountains. The petrology and migmatization of the Moinian are discussed and Dalradian rocks are described for the first time from this area. Reference is made to the structure and brief comparisons are made with adjacent areas. The status of the so-called ‘eclogites’ in the Moinian is also discussed.

The olivine minette described by Tidmarsh from the Holmead Farm, Lox-beare, contains analcite microphenocrysts in addition to olivine, biotite, clinopyroxene and alkali-feldspar. A new chemical analysis shows that the rock is undersaturated with respect to silica. This is still another example of analcite occurring in a potash-rich rock.

Chloritoid and staurolite bearing rocks from the Agnew Lake area in northern Ontario were studied petrographically and with the electron microprobe. A staurolite–chlorite isograd is postulated, above which chloritoid and staurolite coexist in equilibrium, and a Schreinemakers-type petrogenetic grid is constructed to illustrate how the isograd might fit into a paragenetic sequence.

The staurolites from the area are observed to be more ‘siderophile’ than the chloritoids and this suggests that the chlorite participating in the isograd reaction is prograde. This is confirmed in the ‘real’ isograd reaction:

1.559ctd+5.000and+0.009rut+0.058ilm=0.881st+0.039chl+1.366qtz+1.040H2O the coefficients of which are calculated using the mineral analyses of the ideally univariant assemblage staurolite–chloritoid–chlorite–andalusite. Variations in the activity of the unsaturated component ZnO would affect the equilibrium temperature of the reaction and the reaction coefficients.

The sense and amount of rotation of small garnet porphyroblasts is found to vary from place to place on a fold. By correlating this variation with a proposed mechanism of formation of the fold, a tentative profile for the fold at the time of garnet growth is constructed.

The Nahan sandstone of the Nainital district is a soft, fine-grained sandstone of subgreywacke type. Like massive igneous rocks it is very well exfoliated and consists of many concentric layers. Petrographic study of different layers of this sandstone, modal analysis, grain size analysis, and size distribution of the various samples, have revealed that physical processes are mainly responsible for exfoliation of the sandstone. The study of various sedimentary parameters indicated that the provenance is from the schistose and granitic rocks of the surrounding Himalayan mountains and the material was deposited in a shallow slowly sinking basin.

Petrographic and geochronological studies of the rocks of Bulland Hill, an inlier of basement in the Punjab alluvium, are reported. Acid and basic pyroclastic and high-level intrusive types give an Rb–Sr isochron age of 870±40 million years. The previous correlation with the Malani Rhyolite Series of north-western India must be abandoned.

A porphyry boulder from the Permo-Carboniferous boulder bed, probably a tillite, in the Salt Range has the same age as the Bulland Hill rocks.

The Obudu hornblende peridotite is described and briefly compared with similar rock types from other areas. Field evidence, petrographic studies, mineralogical and chemical composition have led to the conclusion that this rock is an independent magmatic intrusion into the hypersthene tonalite (enderbite) with which it is associated, and not a member of a differentiated series.

Zircon populations in quartzo-feldspathic gneisses of the Rhiconich group of the Lewisian are indicative of a sedimentary derivation of the rocks. They are similar to the zircon population of an interbanded quartzite but differ markedly from that of an intrusive granite vein.