the secondary phenomena of
vulcanicity are abundantly manifest; but the great exhibitions of
igneous action, when the plains were devastated by sheets of lava, and
cones and craters were piled up through hundreds and thousands of feet,
have for the present, at least, passed away.

[1] _Geol.-topographischer Atlas von Neu-Seeland_, von Dr. Ferd. von
Hochstetter und Dr. A. Petermann. Gotha: Justus Perthes (1863). Also
_New Zealand_, trans. by E. Sauter, Stuttgart (1867).

[2] Tongariro was visited in 1851 by Mr. H. Dyson, who describes the
eruption of steam.

[3] Mr. Froude figures and describes the two terraces, the "White" and
"Pink," in _Oceana_, 2nd edition, pp. 285-291.

PART IV.

TERTIARY VOLCANIC DISTRICTS OF THE BRITISH ISLES.

CHAPTER I.

ANTRIM.

It is an easy transition to pass from the consideration of European and
other dormant, or extinct, volcanic regions to those of the British
Isles, though the volcanic forces may have become in this latter
instance quiescent for a somewhat longer period. In all the cases we
have been considering, whether those of Central Italy, of the Rhine and
Moselle, of Auvergne, or of Syria and Arabia, the cones and craters of
eruption are generally present entire, or but slightly modified in form
and size by the effects of time. But in the case of the Tertiary
volcanic districts of the British Isles this is not so. On the contrary,
these more prominent features of vulcanicity over the surface of the
ground have been removed by the agents of denudation, and our
observations are confined to the phenomena presented by extensive sheets
of lava and beds of ash, or the stumps and necks of former vents of
eruption, together with dykes of trap by which the plateau-lavas are
everywhere traversed or intersected.

The volcanic region of the British Isles extends at intervals from the
North-east of Ireland through the Island of Mull and adjoining districts
on the mainland of Morvern and Ardnamurchan into the Isle of Skye, and
comprises several smaller islets; the whole being included in the
general name of the Inner Hebrides. It is doubtful if the volcanic lavas
of Co. Antrim were ever physically connected with those of the west of
Scotland, though they may be considered as contemporary with them; and
in all cases the existing tracts of volcanic rock are mere fragments of
those originally formed by the extrusion of lavas from vents of
eruption. In addition to these, t