The following notes are based upon an investigation of the teschenites of the Midland Valley of Scotland, and are an attempt to produce a working classification of the teschenitic intrusions of that area. A comparison has also been made between the Scottish examples and those from some of the type localities of Moravia.

The Midland Valley region of Scotland contains the world's largest known development of igneous rocks carrying primary analcite. These rocks have been described in several publications during the last fifteen years, and some new rock-types have been defined.

During the last summer, whilst mapping the district between Nevin and Clynnog-fawr, I discovered the intrusion which is described in this communication. I can find no reference to it, either in geological maps of the Lleyn or in any geological literature, and conclude that the occurrence has not been placed on record.

At the southern end of Thorney Island, about three miles S.S.W. of Emsworth, in West Sussex, there are low cliffs of London Clay covered by Pleistocene deposits. The London Clay has been folded near the top, and its surface presents a series of basin-like depressions, 3 to 10 feet in diameter, and evidently caused by downward pressure. These basins are occupied by Pleistocene gravel, which contains numerous erratics—many of igneous rocks—and resembles the better-known Erratic Gravel of Selsey. The Erratic Gravel is covered by Coombe Rock and Brickearth, which form the top of the cliff, as shown in the diagram.

During the War a considerable amount of work of a somewhat geological nature was done in the laboratories of Nobel's Explosives Co., chiefly in connexion with providing acid-resisting material for use in the sulphuric and nitric acid plants.

Since the establishment of the two genera Tentaculites and Cornulites by Schlotheim in 1820 their relations have frequently been discussed, but no general agreement has been reached, and their characters have been differently defined by various authors, so that the generic position even of well-known species is rather an open question. For instance, the proper reference of “Tentaculites” anglicus Salter is still somewhat undecided.

In 1916 the writer carried out a field survey of a district in Shropshire in which the “passage beds” between the Silurian and “Old Red Sandstone” are well developed. So apparent was the difficulty of drawing a dividing line between the two systems that a description of the district was published without a decision being reached. Shortly afterwards active service in France and Belgium brought opportunities of studying both field and museum evidence there. The writer came to conclusions which he afterwards found agreed very closely with those reached shortly before by MM. Barrois, Pruvost, and Dubois, who had approached the problem from a different standpoint. A preliminary summary was published, and in 1920 the Council of the Geological Society awarded the author the “Daniel Pidgeon Fund” for the purpose of enabling him to carry out a comparative study of the Downtonian and Gedinnian. The results were laid before the Society in November, 1921. The Council have, however, declined to publish the paper, though their decision in this matter was not communicated to the author until nine months after the reading of the paper. A short summary of the results obtained (but not of the field evidence) has been published in Belgium. The main object of the present note is to place on record the field-work on which the general conclusions are based. One of the principal objections to the writer's conclusions which was raised when the paper was read before the Geological Society was that “the question where the line between the Silurian and the Devonian was to be drawn should be primarily determined in areas in which normal marine conditions had prevailed, not in one of exceptional character, like the Welsh Borderland”.