The purpose of this communication is to draw attention to the possible effect of vast and synchronous volcanic eruptions and associated earth-movement, not only on local but on world climate. It is divided into two parts, the first dealing with the volcanic aspect and its particular relation to climatic changes in East Africa, and the second discussing the wider significance of the proposition and the possibly greater effect of orogenic movements on world climate when associated with volcanic episodes.

The Permian corals of Timor are of particular value on account of their excellent state of preservation which permits of close study of the skeletal structures. The works of Gerth, Koker, and Schindewolf have added much to our knowledge in this respect. In the course of my investigation on the rugose corals as a whole, I have studied a part of the Timor material in the British Museum (Natural History), upon which this present article is based, and I am grateful to the Keeper of the Department of Geology, and to Dr. H. D. Thomas for the loan of specimens, and for the privilege of cutting them in the Museum. Dr. O. M. B. Bulman and Dr. Thomas both kindly read the manuscript. To Professor W. B. R. King and Mr. A. G. Brighton I am indebted for facilities for study in the Sedgwick Museum.

In this country the best known species of Tetradella is T. complicata (Salter), a form which is usually regarded as typical of Caradoc rocks and has been widely quoted in faunal lists as such. It happens, however, that this species was originally described as Beyrichia complicata, by Salter (Phillips and Salter, 1848, p. 352, pi. 8, fig. 16) from the Llandeilo Beds of Llan Mill, near Narberth, and it is extremely unlikely that it ever occurs in Caradoc beds. This confusion has no doubt arisen from the inaccuracies in Salter's original figure, the briefness of the accompanying description and the fact that McCoy figured what is obviously another species of Tetradella under the same name from the Caradoc Beds of Pont y Meibion (McCoy, 1851, pl. IE, fig. 3). At a later date T. R. Jones refigured T. complicata from Llan Mill with more accuracy than Salter and with a fuller description, but unfortunately figured under the same name a form from the Caradoc of Harnage, giving also a list of Llandeilo and Bala localities where T. complicata was supposed to occur (Jones, T. R., 1855, pp. 163–5, pl. vi, figs. 1–5). In addition to this figures have appeared in various textbooks and similar works of a general nature which are usually too poor for specific determination although it is obvious that in the main they cannot be referred to Tetradella complicata (Salter).

During the investigation of certain water-soluble and porous materials it was necessary to produce thin sections showing their structure and crystal composition. Using water as a lubricant during the thinning of the sections the specimens tended to break up and essential constituents were lost through solution, while paraffin had a marked solvent action on the Canada balsam cement resulting in disintegration of the thin section and contamination by particles of carborundum.

In its upper reaches the River Rheidol flows south, parallel to the coast of Cardiganshire, and about ten miles inland. At Devil's Bridge it turns sharply to the west (Text-fig. 1) and enters the sea at Aberystwyth. Due to rejuvenation the river has, in its southward course, incised the floor of its old mature valley the form of which is still clearly visible, and which continues to the south beyond Devil's Bridge to Pontrhyd-y-groes and Tregaron. This part of the valley now contains only small streams.