The classification set forth in this paper is founded essentially on an examination of the junction-beds between the Silurian and the Devonian in the field. All the localities described have been studied personally by the writer, and in most cases the actual junction has been mapped on the 6-inch scale. The names of localities are taken from the 6-inch Ordnance Survey maps, the sheet number being quoted in each case.

The Memoirs of the Geological Survey (355–6) contain a note of the 1866 exposure of the submerged forest at Thurlestone Sands in Bigbury Bay. This is usually covered by sand and (except between half tide and low tide) by a considerable depth of water. The writer has reported to the Authorities of the Geological Survey a further exposure in March, 1923, which they consider “The best exposure that has ever been visible” and which they desire him to put on record.

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”.