The Basal Beds of the Akaroa Volcano. By R. Speight. [Read before the Canterbury Branch, September 6, 1939; received by the Editor. January 8, 1940; issued separately, June, 1940.] Table of contents. A. Introductory. B. Onawe peninsula, description of, and general stratigraphy. C. Features of the general shore-line— I. To the east of Onawe, including a. Lushington Bay, with trachyte and trachyte tuffs. II. To the west of Onawe, including a. Le Petit Carenage to Tikao Bay, with trachyte rocks. D. Chemical analyses of representative rocks. E. The barry's bay—tikao bay shelf. F. Summary. A. Introductory. (See Plate 8.) Akaroa Harbour has long been regarded as a typical caldera, which has been drowned either by lowering of the land or by the rise of the sea. Its floor gradually deepens from mud-flats at its head to 18 fathoms at the entrance, a figure which gives the minimum amount of drowning to have taken place. In the upper portion spurs stretch down the inner slopes with rough centripetal orientation, once having divided stream-valleys, and still dividing them in their upper portions, while the lower parts of the spurs now divide the bays which fringe that stretch of the shore of the harbour. The most striking of these spurs is that which ends in Onawe Peninsula. Taking the bays in clockwise direction round the harbour they are as follows:—Tikao Bay, Le Petit Carenage or Brough's Bay, French Farm, Barry's Bay, Duvauchelles and Head of the Bay, Robinson's Bay, Takamatua or German Bay, Lushington Bay, and lastly French Bay on the shore of which the township of Akaroa stands (see Plate 8). The entrance to the harbour is flanked by bold, vertical cliffs, which rise on the western entrance to a height of about 500 feet; on the eastern entrance they are lower. The harbour presents some resemblance to that of Lyttelton, differing chiefly in so far as it is of later date and therefore has experienced a less prolonged erosion by stream and sea. While the crater-ring of Akaroa is broken down in only one place, viz., the harbour entrance, that of Lyttelton is broken in two, there being no counterpart in Akaroa of the low ridge near Gebbies Pass, where the earliest rocks of the area are exposed as a result of the removal by erosion of the covering of the later andesites and basalts of the Lyttelton system. In both cases the formation of the caldera may be attributed chiefly to the erosion by streams converging on a great central hollow, originally an explosion crater of moderate size, and in both cases there is something of a break in the profile of the inner slopes of the hollow. In the case of Akaroa this lies at an elevation of from 300 to 600 feet above the sea, and is most definite