An examination of existing definitions of facies and subfacies boundaries in pelitic rocks suggests that some alteration is necessary to emphasize two important reactions:

3 Staurolite + 2 Quartz ⇌ Almandine + 5 Al2SiO5 + 3 Water, and

Muscovite + Quartz ⇌ Potash feldspar + Al2SiO5 + Water A generalized plot shows possible relations between the curves of these two reactions and the inversion, curves of the aluminosilicates within the P-T field of metamorphism. The curves of further reactions commonly used to define facies and subfacies boundaries have been schematically added to this plot, and trends of metamorphism in various areas are indicated thereon. P-T curves of dehydration reactions such as the above will vary according to the chemical potential of the water vapour in each particular case. Observations suggest, however, that the curves are not very differently placed from one regional metamorphic terrain to another. That is, the rate of escape of volatiles is broadly similar in the metamorphism of many of these terrains.

Herpetopora Lang is considered to be a junior synonym of Pyripora d'Orbigny, from which Rhammatopora Lang is distinguished by possessing apertural spines. A new species of Pyripora is described from the Albian of Texas.

The contact aureole on the northern side of the Ardara granitic pluton is made up of an outer part where contact effects are slight, and an inner part in which a broad zone of andalusite hornfelses is succeeded towards the contact by a narrower zone of sillimanite hornfelses. The textures of the hornfelses indicate that several phases of recrystallization, some of them associated with phases of movement, took place during contact metamorphism. Certain phases can be correlated with particular episodes in the evolution of the pluton itself.

Some sedimentary structures commonly found at the base of beds of greywacke have been given a variety of names. It is suggested that the name flute-cast be used for scour-and-fill structures, which are shown to be oriented parallel to the direction of sediment movement. Superficially similar structures, described as flow-casts, are formed by movement of the greywacke during and after its deposition; study of their internal structure and their relations to ripple-direction shows them to be oriented at right angles to the current direction.

The history of ideas on boudinage is outlined, and observations in Perthshire are described. Some implications of the “necking hypothesis” are examined.

The discovery of a hitherto unrecorded non-marine lamellibranch fauna from the Tillery Vein of Monmouthshire indicates that this coal represents a horizon at, or near, the junction of the Phillipsii and Tenuis Zones. The characteristics of the seam in a small portion of the North Crop of the South Wales Coalfield are described in an attempt to account for the limited occurrence of these shells.

The cephalic characters which the post-Cambrian trilobite families Encrinuridae, Pliomeridae, Cheiruridae, and Phacopidae have in common are discussed, together with others which illustrate the distinctness of the Phacopidae. The importance of growth-rate studies is emphasized, particularly with reference to the frontal lobe of the glabella. The Calymenidae share most of the features common to the Cheiruracea and Phacopacea, and are considered to be closely related to them, and the Odontppleuridae also share certain features. The possibly neotenous origin of the Cheiruracea and Phacopacea is discussed.

This paper records details of measured sections across the Old Red Sandstone-Carboniferous junction in the neighbourhood of Cardiff.