Canterbury and Westland. 333 



o£ which there are several streams towards the centre of the tunnel, 

 some of considerable size, and which has as high a percentage 

 of silica as 6557, presents some peculiar features not found in 

 any other rocks in the Peninsula. It has a brownish black colour, 

 with a somewhat waxy lustre, and resembles a palagonite tufa, 

 from which it is, however, distinguished by its high amount of silica, 

 which would place it with the trachytic rocks ; small crystals of felspar 

 with a high vitreous lustre are disseminated through it. The small 

 (not uncommon) cavities or fissures are either filled or lined with 

 sph^rosiderite, and some of the joints are covered with a fine coating 

 of the same mineral. 



Returning to the orifice or orifices from which the material for 

 the formation of the caldera wall was ejected, and to which also the 

 numerous dykes, mostly having a vertical position, intersecting it,, 

 can be traced, it appears that the principal focus of eruption was 

 situated a little to the south-west of Quail Island, as the greatest 

 portion of the dykes radiate from here, and the eastern and southern 

 sides of Quail Island, and the shores near Charteris Bay, are formed 

 of tufaceous agglomeratic and brecciated beds, in which a number 

 of angular blocks of rock are enclosed, having all a very bleached 

 appearance. Many of these blocks are trachytic or porphyritic, others 

 are porcelain jaspers and chalcedonies, and the whole has the 

 peculiar altered look of rocks which have for a long time undergone 

 the action of gases, vapour, and heat at the mouth of a volcano. 

 The whole is so intersected with dykes, between which in many 

 instances the bed rock has been washed away, that they look like 

 remnants of the spokes of a gigantic wheel, of which the centre was 

 situated at the spot close to Quail Island, as previously pointed out. 



Another centre of eruption is close to Manson's Peninsula, which 

 consist of quartziferous porphyry. A great number of dykes can be 

 traced crossing that Peninsula, having the peculiarity that they gene- 

 rally stand well out in relief on its western or outer side, whilst on the 

 eastern or inner side they have been washed out ; these dykes are of 

 various thicknesses, ranging from 3 to 25 feet, and have mostly a vertical 

 position, forming protuberances all along the ridge. For the greatest 

 part they radiate from a point in the centre of the shallow bay, 

 situated east of that Peninsula. However, near its northern point 

 the system of dykes becomes more complicated. Pirst, two dykes five 

 and six feet broad, cross each other, of which, the one pointing 



