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trachytic lava. Basalt consists of a minutely-crystalline mass of feldspar mixed with augit; an admixture of greenish grains of Olivin is characteristic of basalt.

In order to gain a clear idea of the history of the Auckland Volcanoes, we must suppose that before the period in which the Auckland Isthmus was slowly raised above the level of the sea, a submarine volcanic action was already going on. The products of this submarine action are regular beds of volcanic ashes, which form highly interesting circular basins with strata always inclining from within outwards. You will at once remember several striking examples which I can mention—as the Pupuki Lake on the North Shore; Orakei Bay in the Waitemata; Geddis’ Basin (Hopua) at Onehunga; and the tidal basin (Waiwhangoa) at Panmure;—Pupuki Lake, believed to be bottomless, has been ascertained by Captain Burgess (who kindly sounded it at my request) to be only 28 fathoms. I call those basins and similar formations, tuff-craters or tuff-cones. The excellence of the soil of Onehunga and Otahuhu is owing to the abundance of such formations, decomposed strata of which form the richest soil that can be met with. It is curious to observe how the shrewder amongst the settlers, without any geological knowledge, have picked out these tuff-craters for themselves, while those with less acute powers of observation have quietly sat down upon the cold tertiary clays.

After the submarine formation of the tuff-craters, the volcanic action continuing, the Isthmus of Auckland was slowly raised above the sea, and then the more recent eruptions took place by which the cones of scoria, like Mount Eden, Mount Wellington, One Tree Hill, Mount Smart, Mount Albert, and Rangitoto, were formed, (and great out-flowings of lava took place. Many peculiar circumstances, however, prove that those mountains have not been burning all simultaneously. It can easily be observed that some lava streams are of an older date than others.) In general the scoria cones rise from the centre of the tuff-craters, (Three Kings, Waitomokia, Pigeon Hill near Howick.) Occasionally, as in the instance of Mount Wellington, they break through the margin of the tuff-crater.

The Crater System of Mount Wellington is one of the most interesting in this neighbourhood, as beautifully shown by the large map, which Mr. Heaphy has kindly prepared for me from actual survey. (There are craters and cones of evidently different ages. The result of the earliest submarine eruptions is a tuff-crater.) The Panmure road passes through the tuff-crater, and the cutting through its brim exhibits beautifully the characteristic outward-inclination of the beds of ashes; elevated from their former horizontal levels by the eruptions, which threw up the two minor crater cones south of the road—one of which is now cut into by a scoria quarry. After a comparatively long period of quiescence, arose from the margin of the first crater system the great scoria-cone of Mount Wellington, from whose three craters large streams of basaltic lava flowed out in a Westerly direction, extending North and South along the existing valleys of the country, one stream flowing into the old tuff-crater, and spreading round the bases of the smaller crater cones. The larger masses of these streams flowed in a South-westerly direction towards the Manukau; coming into contact with the older and long-before hardened lava streams of “One Tree Hill.” The traveller on the Great South Road will observe about one mile east of the “Harp Inn” the peculiar difference in the colour on the road, suddenly changing from red to black, where the road leaves the older and more decomposed lava streams of One-tree Hill and passes on to the new and undecomposed lava streams of Mount Wellington. The farmers have been able to avail themselves of the decomposed lava surface, which is now beautifully grass-covered, but not of the stonefield of the newer Mount Wellington and Mount Smart streams.

The Caves at the “Three Kings,” Pukaki, Mount Smart, Mount Wellington, &c., are the result of great bubbles in the lava streams—occasioned probably by the generation of gases and vapour as the hot mass rolled onward over marshy plains. These bubbles broke down when their thinnest part—the roof—and the way into the caves is always directly downward.)

Examples of every gradation may be seen—from the simple tuff-crater without any cone, to those which are entirely filled up by the scoria cones. Especially interesting are those which may be said to represent the middle state, in which there is a small cone standing like an island in a large tuff-crater, and surrounded by either water or swamp. Perhaps the most perfect specimens of this kind occur at Otahuhu and near Captain Haultain’s; a map of which, from actual measurement, has been prepared by Mr. W. Boulton. You need not be alarmed when I tell you, that even the very spot on which we are assembled is the centre of an old tuff-crater, from which fiery streams once issued, and which has thrown out its ashes towards the hill on which the barracks stand.

In order to account for these various shapes, it must be borne in mind that the cones of scoria were once higher, but on the cessation of volcanic action they sunk down in cooling, and some entirely disappeared.

That the Auckland volcanoes were, in the true sense of the word, “burning mountains,” is proved not only by the lava-streams, which are immense in comparison to the size of the cones, but also from the pear-shaped volcanic bombs which, ejected from the mountain in a fluid state, have received their shape from their rotary motion through the air. That the eruptions of the Auckland volcanoes have been of comparatively recent date, is shown by the fact that the ashes everywhere occupy the surface, and that the lava-streams have taken the course of the existing valleys. (*This is beautifully exemplified by the probably simultaneous lava streams of Mount Eden, the Three Kings, and Mount Albert, which, flowing through a contracted valley, meet altogether—on the Great North Road—and form one large stream to the shore of the Wai-