Canterbury and Westland. 331 



agglomerate. In other instances the rough, uneven scoriaceous surface 

 of the lava-streams has been well preserved, the hollow spaces being 

 filled up bj ashes and ejecta, in which case they resemble many 

 of the recent lava-streams which I examined in Mount Vesuvius and 

 Mount Etna shortly after they had issued from the crater. 



From the cliffs outside Lyttelton Harbour and at Sumner a very fair 

 idea can be gained how the whole assemblage of beds was formed, the 

 lava-streams and agglomerate beds in turn filling up pre-existing 

 hollo ws, and thus forming and equalising the surface. In other sections 

 it is observable that when the lava-streams were flowing at a higher 

 angle than usual they shrunk considerably, whilst where hollows were 

 in their course, which they usually filled out, they became very thick. 

 The lava of which the caldera wall under consideration has been built 

 up, consists of basic rocks, changing from a dolerite to a fine-grained 

 basalt. Some of the lava-streams, however, as previously pointed out, 

 show also a remarkable difference in the structure of the rock of which 

 they are composed, the central portion being a compact basalt with a 

 few crystals of augite, basaltic hornblende, and labradorite, whilst the 

 upper portion consists of a lighter coloured porphyritic dolerite, some- 

 times so replete with good-sized crystals of labradorite that the greater 

 portion of the rock is formed of that mineral. Again, most of the 

 lava-streams on the inner slopes, or on the rim of the caldera wall, are 

 of a compact basaltic nature, and consist, lower down and more distant 

 from the centre of eruption (becoming at the same time much thinner), 

 of a greyish doleritic rock full of crystals of labradorite, augite,* 

 basaltic hornblende, and rubellan. Even in the most compact streams 

 olivine is seldom present. 



There is a great difference in the texture and character of the rocks 

 forming the innumerable lava-streams, according to the conditions under 

 which they have cooled and consolidated, so that, judging from hand 

 specimens only, a great variety of rocks can be made out. However, 

 as it is possible to follow in many lava-streams the gradual change 

 from a compact black basalt into an almost earthy or scoriaceous 

 vesicular lava, passing through all the varieties of a porphyritic or 

 crystalline granular compound, which could be claimed as anamesites 

 or dolerites, I have thought it best to include the whole series under 



* In some of the tufas, augite in well formed crystals, often of large siae, is not of unfrequent 

 ■occurrence. 



