Art. XXXI.—The Auckland Volcanoes. By Hugh Shrewsbury, M.A. [Read before the Auckland Institute, 2nd November, 1891.] Plate XXXV. The isthmus which separates the Waitemata and Manukau Harbours, and upon which stands the City of Auckland, has an average breadth of six miles; but at its narrowest part, between the eastern shore of the Manukau and the Tamaki River, it is not more than a mile and a half in width; and, again, between the Whau River and the Manukau its breadth is only about two miles. Small as this tract of land is, however, it is thickly studded with extinct volcanoes, there being no less than sixty-three separate points of eruption within a radius of ten miles, in many places so close together as to merge into one another. The greater number of these volcanic cones are in a very perfect state of preservation. It is true that many of them have been deeply terraced by the Maoris for purposes of fortification; many also have been cut into to obtain supplies of road-metal; but from weathering and denudation these hills have suffered little, and are remarkably well preserved. They present the form of cones of low altitude, Rangitoto, the highest of them, being only about 920ft. in height, and the slope of their sides being about 30° or 40°. The majority of them are dome- or mound-shaped rather than conical. Classifying them according to their mode of formation, we may divide them into three classes: (1) tuff cones and craters, (2) scoria cones and craters, (3) lava cones. 1. Tuff Cones and Craters.—Instances of these are Lake Takapuna and the Orakei and Panmure basins. They are readily distinguished from the scoria-cones by their shape, being wider and flatter, with much larger craters. The material composing them is not, as in the case of the scoriacones, entirely scoria and lava, but consists of a mixture of sand and grit of non-volcanic origin, derived from the Waitemata beds, with volcanic blocks, scoriæ, lapilli, and ash, in some cases the former, in others the latter, class of material predominating. Some of the tuff-craters have been partly filled up by scoria-cones thrown up by subsequent eruptions—for example, Mount Wellington and the North Head—and it is probable that many of the scoria-cones stand upon older tuff-craters, which, however, are hidden from view by the great quantities of lava and scoria ejected by the later eruption.