502 Transactions,—Geology, 
the Lyttelton-Sumner road at right-angles, on the very summit of Evans 
Pass, and which is repeatedly passed by the road winding in and out of the 
different bays before reaching that pass. It can be followed to Taylor’s 
Mistake. Everywhere along the sea cliffs at and near the entrance of 
Lyttelton Harbour, numerous dykes, mostly all in a vertical position, can 
be seen pointing towards the centre of that harbour. A few, however, 
stand in a slanting position, and others have a tortuous course, As one of 
the remarkable changes which some of the dykes have undergone since their 
formation, I may also mention one which is well exposed in the sea cliffs at 
Ohinitahi, Governor's Bay ; here a dyke of domite, about nine feet broad, 
crosses in a nearly vertical position the so-called trachyte sandstone de- 
posited on the slopes of the quartziferous porphyry. After its solidifica- 
tion, a new fissure, about three feet broad, has been formed parallel to its 
direction, and running along its centre, which has been injected from below 
by domitie matter, but slightly different from the former ; however, instead 
of continuing to the top of the cliff, about twelve feet above the sea level, the 
dyke is seen to turn from its vertieal to a nearly horizontal position, and to 
thin out considerably at the same time, disappearing altogether when it 
touches the side wall of the bed-rock. The older dyke, above this change 
of direction, is considerably shattered and broken. 
Before proceeding, it wil perhaps be useful if I offer a few remarks on 
the eauses which led to the formation of these remarkable dykes. I con- 
sider this the more important, as nowhere, as far as I am aware, do they 
exist in such great numbers, nor do they possess such a large longitudinal 
extent, as in the volcanic system under consideration. It appears to me 
that the immediate cause of the formation of a radiating system of dykes 
may be traced to the choked-up vent or chimney of a volcano, the mouth 
of which, after an eruption of considerable dimensions, is thoroughly filled 
up, either by its sides falling in, by the cooling of ascending lava-streams, or 
by both causes combined. When, from abyssological origination, masses of 
steam and gases have collected below this vent, and new matter is ready to 
be erupted, an enormous effort of nature will be necessary to clear out the 
old, or form a new chimney, which cannot be accomplished without a series 
of violent earthquakes, succeeded by an enormous explosion, by which the 
mouth of the voleano is cleared out or newly formed, and of the magnitude 
of which we can scarcely form a conception. A similar effect, on a gigantic 
scale, must have been produced repeatedly by the compressed masses of 
gases and steam during the formation of the Lyttelton caldera wall, when 
the upper portion of the closed-up voleano was not only removed, but vast 
quantities of ashes, scorie, and lapilli were thrown out, together with lava- 
streams which flowed in various directions. Before, or during these 
