While engaged this autumn in reinvestigating the relations of the “Dingle Beds” and “Glengarriff Grit Series” to the Silurian rocks below, and the Old Red Sandstone above, in the South-West of Ireland, my mind naturally reverted from time to time to the Devonian district, and the succession of its beds, upon which there has recently been so much discussion, and to which the late Professor Jukes devoted so much time and labour. With him I agree in believing that the key to the solution of the Devonian problem is to be found in the structure of the South of Ireland, though with reference to the actual explanation which he proposed, I can only see my way to a partial concurrence.