Dinas Head is a small promontory adjoining Trevose Head, some five miles west of Padstow on the north coast of Cornwall. Petrographical attention was first drawn to it by Howard Fox, who in 1894, noted the development of albite-rich rocks between greenstone and slate, and he concluded that the rock was an adinole. He also noted the peculiar spherulitic development of albite giving some rocks an igneous appearance, but, on account of the fine banding preserved in these rocks, he concluded that they were metasomatized sediments. This conclusion was subsequently supported by McMahon and Hutchings. The Memoir of the Geological Survey of the Padstow and Camelford district agrees with Fox as to the origin of the adinole, and points out the exceptional thickness of its development when compared with other greenstone-slate contacts.

The systematic classification of the potash-soda-felspars is of the greatest interest and importance to the mineralogist, but problems demanding physical investigation are raised in work carried out recently by Dr. Edmondson Spencer, who has described the results of exhaustive chemical, optical, and thermal investigations of a representative collection of these minerals. Dr. Spencer has very kindly allowed us to examine by X-ray methods a large number of his specimens, so that for the first time it has been possible to make a fairly complete survey of potash-soda-felspars of known chemical composition and with accurately measured optical properties.

This paper presents the results of our general survey of potash-soda-felspars with compositions ranging from nearly pure potash-felspar to approximately 50 % soda-felspar. The natural minerals, and the same minerals after specified heat-treatment, have been examined. We do not discuss in detail the interpretation of our results in terms of the atomic structure of felspars; the subject is extremely complicated, and it is necessary to await the results of other investigations now in progress in this laboratory before attempting a complete structural interpretation.

The specimen, which is in two pieces cemented together, was purchased for the Museum of Practical Geology in February, 1888, from Mr. F. H. Butler, and bears the Museum's original Mineral Inventory label (M.I. 5714) on each portion. The inventory description is “Tin-stone, well crystallised, coating granite, Beam mine, Cornwall”. The exhibition label mentions quartz, and the presence of beryl had no doubt been overlooked through the general resemblance to milky quartz, which is not uncommon on some Beam mine material. Actually it was noticed during the rearrangement of the collection in 1934 that the cassiterite is accompanied by large, dull white crystals which proved to be beryl. In view of the rarity of beryl in Cornwall a brief description may be of interest.

The author arrived at Huckitta station, 135 miles north-east of Alice Springs, towards the end of June, 1937, on an expedition to the Tarlton Range at the north end of the Simpson Desert. The manager of the station, Mr. W. Madrill, said that a haft-caste named Mick Laughton employed on the station had a stone he would like to show, and this was produced by Laughton in the usual diffident manner of the half-caste. It proved to be a flat, rusty mass weighing a little over nine pounds. A few knocks with a hammer soon showed it to consist in part at least of malleable iron, and a meteorite was at once suggested. The specimen was not very closely examined, and the olivines, which show up so excellently on the polished surfaces, were entirely overlooked, which is quite easily done in the case of the iron-shale or the more weathered natural surface of the meteorite, although olivine makes up more than half the volume. It was said that the specimen came off a big stone which stood several feet out of the ground.