Canterbury and Westland. 329 



being uncommon. It is evident that the building up of such a huge 

 system during numerous eruptions, often of great magnitude, could 

 not be accomplished without a great destruction of portions of the beds 

 previously formed, taking place, the point of eruption in the crater 

 shifting continuously about the centre. If, at the same time, we 

 examine the lava-streams and the interstratified agglomerate and ash 

 beds along the water's edge, we have to coma to the conclusion that 

 all the eruptions by which the caldera wall was formed from summit 

 to bottom, occurred under the same physical conditions. 



For forming a true conception of the manner in which the crater 

 wall of Lyttelton Harbour was raised, I cannot do better than refer 

 the reader to the observations which have been made by excellent and 

 competent geologists of the changes which occurred in Mount Vesuvius 

 and Mount Etna in recent times, during violent eruptions. It has been 

 made evident that these eruptions, principally at the beginning, could 

 not have occurred without great convulsions taking place in the earth's 

 crust, so that earthquakes of considerable vehemence must have pre- 

 ceeded them. After the crater was once formed, by the ejection of 

 lapilli, scoriae and ashes, over which streams of stony lava had been 

 cooling, so as to preserve them from destruction, it existed either in 

 the form of a large cauldron filled with liquid lava, resembling some of 

 the volcanoes in the Sandwich Islands, or after partial solidification it 

 formed a large rocky plain with a number of smaller vents over which 

 ashcones were built up, or with numerous fissures from which vapours 

 and gases issued such as, before the great eruption of 1822, the crater 

 of Vesuvius appeared, as described by Sir Charles Lyell in his Classical 

 Principles of Greology. During that eruption, the whole of this rocky 

 plain was blown out, and an immense abyss formed, which was partly 

 filled up by portions of the walls, more than 800 feet of which had 

 been carried away by the explosion, so that the altitude of the mountain 

 was reduced from 4200 to 3400 feet. Similar occurences have without 

 doubt repeatedly taken place during the building up of the Lyttelton 

 caldera wall. Examining into its formation and beginning our obser- 

 vations in the harbour, we find that many lava-streams have been 

 preserved which have cooled in their ascent ; others lie horizontal for a 

 short distance, and are then seen to descend, conforming to the 

 gradient of the underlying lava-streams, or agglomerate beds. In 

 many instances we have also clear evidence, that considerable destruc- 

 tion of the beds previously formed had taken place before new streams 

 flowed over the lip of the crater, or before beds of ashes, scoriae and 



