both a younger and an older period in other places in New Zealand

In this zone are found volcanic rocks of a very interesting character of great variety and of different ages.

The older rocks, by which the high chains to the west of this extensive volcanic zone have without doubt been brought to their present almost vertical position, are trachytic.

When this eruption took place large masses probably were in a pastelike semi-fluid state, ascending through huge fissures. Not the least sign of craters or scoriacious lava streams are to be observed. The mountains formed by these rocks are from 3000 to 5000 feet high and have generally soft rounded outlines, the highest points only having a tendency to assume a dome-like form.

The principal mountains consist mainly, as observed by me at the base of Mount Somers, on Snowy Peak, and Mount Misery in the Malvern hills, of a peculiar kind of trachytes, which, from their lighter specific gravity, their felsitic matrix, and the great amount of silica, sometimes amounting to three-fourths of their constituents, distinguish them not only from the heavier basic volcanic rocks, but also from the trachytes properly so called.

Their resemblance to certain granites is often so great, and their analysis so nearly identical, that there is no doubt, they have been derived from the same abyssological sources. Baron Richthofen has given to them the name of rhyolites, and I shall, in future, use this appropriate name to distinguish them from the other trachytic rocks abundant in the Province.

Quartz in small crystals or grains and even in larger concretions is very abundant, and may, as a rule, be considered to be their distinguishing feature, although sanidin (glassy felspar) also occurs. In colour they are generally white or pale green, but they also present many varieties of lighter shade.

Their lithological character changes constantly, sometimes becoming pearlitic or obsidians, the latter with a spherulitic structure without doubt the result of slower or quicker cooling of the erupted masses. They seem partly to have filled fissures formed in the main mass, and then present a more felsitic structure or to have flown from openings at their sides, in which case they generally present a pearlitic structure.

Silica, in the forms of rock crystal, amethyst, calcedony, heliotrope, agate, cornelian, jasper, semi-opal, and chrysoprase are very abundant. They either line fissures or form godes or concretions (lythophyses) and such masses have been left exposed by the decomposition of the softer body of the rock, so that some mountains, as for instance Snowy Peak, are literally strewed with these siliceous minerals. Some rocks of an amygdaloidal structure have their hollows filled up, partly with calcedony, partly with a siliceous green earthy substance (pimelite.)

Sometimes thin plates of calcedony are met with, having on both sides the impressions of crystals of calcareous spar. In rare instances I found pseudomorphic crystals of the calcareous spar, the carbonate of lime previously deposited in these fissures, having been decomposed by water surcharged with silica, which deposited the latter mineral without destroying the forms of the original crystals.

No sign of silica, in the form of quartzinter or geysertie was met with, so as to indicate that boiling siliceous springs, such as still exist in great activity in similar volcanic zones in the Northern Island, have here been at work.

In other places true trachytes occur, often with tabular and other very interesting structures, but having only cursorily and during the middle of winter examined this district, I am not yet prepared to say in what relation they stand to the more extended rhyolites of this volcanic zone. At the base of the systems above described we meet with large beds of tufa, often so much resembling the rocks from which they have been derived, that they look more like decomposed volcanic rocks than mere aqueous deposits.

Some are well stratified, forming ribbon-tafas of great beauty and variety. In other places they become so coarse as to present the appearance of agglomerates.

It is evident, that during a long period these volcanic rocks remained deeply immersed in the sea, during which time the extensive tufa beds, several hundred feet in thickness, were formed. A change then took place however, oscillations occurred, which made the water shallower and deposits of another nature were formed, in which also the disintegration of the western paleozoic rocks participated. By these various processes, of deposition on the one hand and upheaval on the other, dry land made its appearance, whilst some of the strata thus formed consisted of loose ferruginous sandstone. A luxuriant vegetation then overspread it for a long period, until, by a fresh depression of the ground, it was again buried below the sea level, giving birth to the extensive lignite beds found all along the margin of the volcanic zone.

That in some places oscillation occurred by which the dry land alternately became sea bottom, is shown by the existence of small seams interstratified with marine deposits, whilst that other places were not affected by these changes is shown by the existence of one large seam of lignite.

The downward motion, however, was exceedingly slow, as is shown by the character of the numerous fossils imbedded in the strata, which all have a littoral character.

They are inclosed in limestone, sometimes very compact, sometimes of a more earthy nature, or consisting of a mass of broken and rolled shells, cemented by an argillaceous or calcareous matrix.

Above these large oyster beds occur, which, by their hardness have better resisted the destroying action of the atmosphere than those lying above them, which are of a much