The importance of accurate knowledge concerning the causes of composition zoning in plagioclases lies in the possibility that such zoning may throw light on the magmatic history of the rock of which the zoned felspar is a component. The interpretation of plagioclase zoning has been the subject of much speculation among petrologists, Phemister having recently contributed (1934) a valuable discussion of earlier work, together with certain new suggestions as to the probable causes of the reverse and oscillatory types. My own attention was drawn to oscillatory zoning while studying the Upper Devonian igneous complex of Marysville, Victoria (Hills, 1932, pp. 152, 153), and I found the hypotheses suggested by Phemister and by Harloff (1927) to explain this enlightening. Nevertheless, it seems to me that the real significance of some of the processes postulated by both these workers has not been correctly indicated, and that the mechanism proposed by Phemister to account for oscillatory-normal zoning is not theoretically possible. Since it is important that the physico-chemical basis of such hypotheses be sound, a discussion of Phemister's and Harloff's theories, and certain other possible causes of reverse zoning is given below.

It is now about forty years since the completion of the late Sir Aubrey Strahan's Geological Survey Memoir on the Isle of Purbeck and Weymouth, published in 1898. All those who, like the present writer, have known the Dorset coast from boyhood and have carried Strahan's maps and memoir over most of the ground many times cannot have failed to learn from them lessons of incalculable value. They will have come to regard the memoir as a model of scientific method and of lucid presentation, a classic not to be questioned save in matters of palaeontology, now necessarily out of date.

For our present purpose the Craignish Area is considered to include the peninsula of Craignish and its adjoining parts, as shown in the sketch-map, Text-fig. 1.

A Brief account of this dyke was published in 1933, but since that time further studies, with assistance from Dr. A. E. Mourant and Mr. A. J. Robinson, have been made, and the results seem to be of sufficient value to justify a return to the subject.

Since my last note appeared upon the series of deposits which fills the Ebbsfleet Channel of post-Early Mousterian (Levalloisian) age further excavations have been undertaken this year which have resulted in the complete sequence being established. It had been observed that the Trail with “ rafts ” of Coombe Rock, which overlay the flood-loam of temperate facies (deposit 8), sometimes contained in its upper portion “ rafts ” of a pale sandy brickearth; moreover, here and there, traces of this same faintly stratified brickearth occurred upon the surface of the Trail in question. In order that the true explanation of these observations might be reached, a special excavation was made at what was considered to be the most suitable spot at the site.