The collection of mollusca dealt with in this paper was made by Dr. W. A. Macfadyen during his survey of the Farsan Islands, Kamaran Island, and the adjacent Arabian coast in the winter 1926–7. An account of the geology has been given by him in Part 1 of the paper, while Mr. A. G. Brighton will be contributing a section on the fossil echinoids. Dr. Macfadyen's investigation has shown that the islands are composed mainly of fossiliferous strata of late Cainozoic age. It was found possible to make out a definite succession, broken by local unconformities, and a good collection of fossils was made from each stratigraphical subdivision in the hope that definite evidence of the age of the beds would be obtained. The only previous contribution to the palaeontology of the area is a paper by Jousseaume (1888), which includes an account of twenty-five species of “raised beach” mollusca collected by Faurot on Kamaran Island. One of these—a Spondylus—is described as new, but the remainder are referred to living Indo-Pacific species. It appears from Faurot's description (1888, p. 534) that these shells came from the top bed of the Reef Limestone of Dr. Macfadyen's classification. Lists of the species present in Dr. Macfadyen's collection are given in the second part of the present paper, but these will be preceded by a short discussion of the general results of the investigation, and also of our present knowledge of the molluscan fauna of the late Cainozoic deposits of the Erythraean region.

The weathered surfaces of the limestones and calcareous shales of the Lower Lias in Somerset and Dorset sometimes exhibit curious paired markings. On careful examination these prove to be cross sections of U-shaped burrows of organic origin, appearing as two circular markings connected by a shallow depression or by a slight variation in the character of the matrix. Similar burrows have been described from the Lower Estuarine sandstone of Blea Wyke, on the Yorkshire coast. Dr. F. A. Bather has discussed their origin and structure in detail and has assigned them to the genus Arenicolites, which was established by J. W. Salter for “all worm burrows with double openings”. Other species of the genus have been described from arenaceous and argillaceous beds of Longmyndian, Ordovician, and Upper Carboniferous age, but as far as the author is aware, the species here recorded is the first that has been mentioned from the calcareous rocks of the Lower Lias of England.

In a previous paper published in the Geological Magazine, the writer made an attempt to discuss the mechanism of earth movement on a continental scale purely from a tectonic point of view. The problem is so vast and involved that some of the vital points were hardly touched upon, partly because of lack of space and partly of literature. The arrival of the admirable works of Dr. A. du Toit and Dr. E. Krenkel has enabled the writer to deduce the mechanism of the movements of South Africa directly from its tectonic features, which process is thought to be far more reliable than the type of argument used in the previous case although the results arrived at are essentially the same. The earlier movements in North America are now seen to furnish evidence of the same type of mechanism as that which staged the later movements. An epsilon type of structure has been recognized in Eastern China, which was then described as a mere arc. The problem of the distribution of concealed coalfields in England was in the previous paper barely touched upon. It is now proposed to consider some of the critical points bearing on the problem.

During the summer of 1928 I spent a month making a detailed study of the metamorphic condition of the rocks in the magnificent section displayed along the Banffshire coast and in the immediate hinterland, and this work has been supplemented by examination of a number of rock slices cut from specimens then obtained, and also of those in the collection of the Sedgwick Museum mostly collected by Mr. Harker.

In a recent number of the Records of the Geological Survey of India, vol. lxii, p. 410, Dr. Fermor has done me the honour to draw attention to a paper of mine (Geological Magazine, 1903, p. 305) in which I came to the conclusion that the thrust-plane at the base of the Himalayas must have, at its outcrop, a dip of about 14°; and he points out that this estimate agrees with the observations of Mr. Middlemiss in Jammu Province. My estimate was based upon a simple geometrical deduction which proceeds directly and inevitably from the assumption that the Himalayas rest upon a plane thrust-surface.