It is still fresh in our memory that the Geological Society of London made a bold attempt a few years ago to arranga a wide-ranging discussion on the problem of continental drift. On an occasion of this nature one might be tempted to imagine a scene as lively as that when the Wernerians and Huttonians met at the Castle Hill of Edinburgh. But the opponents of the hypothesis, as the report revealed, seem to have stood no less firm than do the continents, as they hold. One looks in vain, since the publication of the American Symposium, for a change in the trend of opinion. This, however, does not mean that the problem is closed. We thus welcome the fresh lead given by Dr. A. L. du Toit in his recent volume on Our Wandering Continents.

This well-known genus presents a nomenclatorial problem apparently even simpler than that of Mortoniceras, dealt with in the first article of the present series, yet I can foresee considerable opposition to the views here put forward. It is, of course, agreed that “names now current are not to be discarded unless the reasons for change show a clear-cut necessity” (Opinion 93); but since “priority of actual date” is quoted as an example of such necessity, I consider that we shall have to change our present interpretation of Pachydiscus, however irksome the change may be to some.1

In recent years much work has been done in determining the quantitative—or more strictly “numerical”—composition of heavy mineral residues from sedimentary rocks in the hope of obtaining evidence as to whence the detritus was derived. It is clear that the petrological characteristics of the land mass whose erosion provides the detritus must always be an important factor in predetermining the percentage composition of the residue as we now find it. Yet the sorting action of the transporting agents (which tend to separate the heavy from the less heavy minerals) and of chemical agents (which, both before and after deposition, destroy some minerals and introduce new ones) may often be suspected of having a great or even a dominating influence upon the final composition of the residue. It is proposed in this paper to investigate by simple mathematical methods the probable effect of these processes and to do so along lines which have been suggested by the study of actual heavy mineral assemblages.

The western peninsula of Cyprus, which is known as Akama or Akamas, is somewhat inaccessible and its geological features little known. It was not visited by the present writer in 1929, but Mr. C. P. Manglis, mining engineer of Nicosia, has recently traversed it and collected specimens of a fossiliferous Miocene limestone with interesting characters in places where no fossils had previously been found, and he informs me that a ridge of the Trypanian Series outcrops along the central part of the peninsula (though this is not indicated on Bellamy's map), and that there is also an abundant effusion of andesitic lavas. The limestones are white in colour and mostly hard, compact, or semicrystalline; they contain massive compound corals, generally in a poor state of preservation, their internal structure being often largely obliterated. Apart from corals, the rocks have only yielded a few large boring Lithodomi and some indeterminable small fragmentary impressions or casts of small gasteropods and lamellibranchs. It is to be remarked that Gaudry recorded' from the Miocene of Cyprus only one species of coral, Astraea [Orbicella] guettardi Defr., and that was from another part of the island. But limestones containing corals similar to those collected by Mr. Manglis occur in various parts of the Mediterranean basin, and we may especially compare those species described by Felix, Daus, Schaffer, Oppenheim, Blanckenhorn, Gregory, and Kühn from the Miocene of Asia Minor, Syria, Persia, Egypt, and Cyrenaica. The Miocene corals of Cilicia appear to be in, many cases identical with those in this collection, and bearing in mind the proved tectonic relations of Cyprus with the mainland, this is what we should expect. The literature on these Miocene corals is very extensive, and Kiihn has recently (Palaeontographica, lxxix, Abt. A, 1933) given a useful list of references which have been consulted in identifying the specimens in this collection.

In my publication On the Mechanism of the Geological Undulation Phenomena, etc.1 I discussed on pp. 69–73 the different characteristics of flat-dipping compaction folds and of folds caused by folding during sedimentation.

Professor Reynolds has recently described from one of the Arnold Quarries, Chipping Sodbury, a section in which several beds of the Carboniferous Limestone were seen individually to be thrust over, or underthrust by, Rhaetic deposits (Text-fig. 2).1 No decision was made as to the origin of this structure.

Almost twenty years ago the writer mapped the series of late-Glacial drainages in the area immediately south-west of Newcastle-upon-Tyne (1).

For many years past the writer of the present note has devoted much thought to the problem of the origin of sedimentary series of enormous thickness, such as occur or are said to occur in many parts of the world. In one group of instances the answer is easy: that the great thickness is apparent and not real. Such for example are some types of delta deposit, where the material has been laid down on a submarine slope in a manner analogous to the formation of a railway embankment or a slag heap, by tipping trucks over the end. Here obviously the total attained by adding together the thicknesses of all the inclined layers is quite misleading. This effect may be seen in the foreset beds of almost any deltaic deposit on almost all scales, and its true nature is generally revealed by the occurrence of topset or bottomset, more or less horizontal beds above or below. This effect is very well seen on the south coast of Devon westwards from the mouth of the Exe, where for some miles the bright red New Red Sandstone strata, usually considered to be Permian, dip consistently eastwards at 25 or 30 degrees. The conditions of formation of these brilliantly red strata are obscure, but in one railway cutting at the eastern end an obvious horizontal topset bed proves clearly that the dip is deceptive, and that the real thickness at that point need not be much more than the small depth of the cutting.

Discussion of the genesis of kyanite-amphibole associations in amphibolites has so far been limited to assemblages involving common hornblende (1). Striking examples of an association of kyanite with rhombic amphibole (gedrite) now known from the Archaean gneisses of the White Sea area, Russia, visited by the Northern Excursion of the International Congress in 1937, probably provide one of the first records of this paragenesis in the literature.1 The rocks of the region include coarse-grained garnet and kyanite rich gneisses associated with amphibolites in the Shueretsky district of Karelia, and have been described by Ignatiev (2).