The Millstone Grit and Coal Measure rocks of West Yorkshire include a series of sedimentary ironstones characterized by the spherulitic habit of the siderite. These rocks have been examined in detail in Airedale and Calderdale, and in brief visits to East Lancashire and South-West Yorkshire the author has recognized a similar development of ironstones, and so believes that the substance of this paper may be generally applicable to the whole of the central and southern Pennine region.

It is proposed in this communication to describe the results obtained, and methods employed, in an investigation of the British strand-line oscillations and to discuss related episodes on the Continent. The original object was to determine the nature of the movements and, if possible, to discover their time relations, but the unexpected correlations that emerged rendered it necessary to extend the scope of the investigation. The data available include the pre-Glacial, 100-ft. and 25-ft. raised beaches together with the knowledge that the land stood high above the prevailing sea-level and was glaciated between the first and second beaches mentioned, and that there was a re-advance of the ice between the second and third. The most interesting feature of the oscillations is that they constitute a complete cycle; for the sea which left the pre-Glacial beach at the beginning of Quaternary time, practically returned to it at the close. This cyclic nature of the movements suggested that if the first, or determining, movement could correctly be assumed, it should be possible to depict the changing relations of sea and land in a simple bi-axial diagram; the movements being given absolute value by reference to the earth’s centre.

The structure of the earth was supposed by Suess to be tripartite, there was an outer layer of rocks mainly granitic, the sal, or sial as it is usually now called. This rested, or “floated”, on a dense layer called the sima, of basaltic character, within which was the earth’s core, or nife, metallic in nature. Such a simple conception has been modified in the light of later knowledge: geologically there is much evidence pointing to the existence of several shells of increasing density within the crust. This is to some extent supported by the evidence of seismology, the layers below the upper sedimentary layer being the Granitic, the Intermediate (of tachylyte or diorite) and Lower Layers (dunite, peridotite, or eclogite) (1). According to the latest information there are four layers intermediate between the granitic and lower layers: the thickness of the sedimentary layer varies from about 2 to 6 kilometres in mountainous regions: the thickness of the granitic layer varies, being about 10 to 12 kilometres in Central Europe. In low-lying regions the total thickness of these two layers is probably about 6 kilometres less than in mountainous regions: “the thicknesses of the other layers are very difficult to determine; the upper two probably have together a thickness of about 15 kilometres, but the others can hardly be determined from the observations” (2).

The base of the Phillipsi Zone, which Professor Trueman has made the base of his Upper Westphalian, is taken at the horizon of the Shafton Marine Band in Yorkshire (1) 1 and in consequence the following beds are included in this zone:—