Maeshall. — Oil Tridymite-Trachyte of Lyttelton. 371 



shore of the harbour, there is a small cliff of the same rock, 

 ■with several small sea- worn caves. The cliffs continue to 

 bound the shore to the point H, whence it slopes up the hill 

 to K, which was our starting-point. 



There are four well-defined dykes in this rock, three of 

 which, M and N, on the shore, are of small size, while the 

 fourth, which cuts into the outcrop K, is 6ft. to 7ft. wide. 



At the top of the hill there is clear evidence of a large 

 dyke, which runs parallel to the length of the hill, along 

 its summit. In breadth the dyke measures about 20ft., and 

 in length about 200 or 300 yards, its bearing being E. 41° N. 



It is evident that the trachyte lava issued from this dyke, as 

 outcrops are found the whole way from the top to the bottom, 

 and are generally of a vesicular character. If, as Sir J. von 

 Haast suggests, it flowed from a central crater, situated near 

 Qaail Island, it would necessarily, like the other rocks of the 

 harbour, present a single face of moderate breadth, and of a 

 tolerably constant altitude above the sea-level. 



It is possible that the lava flowed from a crater that occu- 

 pied the position where the Town of Lyttelton now stands. 

 This, however, is highly improbable, as no independent evi- 

 dence exists of the activity of a vent situated there. No 

 system of dykes has been discovered ; none of the other hills 

 enclosing the depression afford evidence of such a vent, while 

 on one side all traces of crater- walls, if they ever existed, have 

 been removed. 



The very appearance, too, of the hill under consideration 

 gives one the idea that its origin is not the same as that of 

 the others, for, while its surface is, generally speaking, smooth 

 and rounded, and resembles the slopes of Mount Herbert, the 

 others, almost without exception, present that series of sharp, 

 steep walls rising tier above tier that so plainly indicates to the 

 geologist that they are formed of lava-flows lying one over the 

 top of another with a moderate angle of inclination. These 

 considerations, and the fact that a well-defined dyke exists at 

 the summit, must remove all doubt as to whether an inde- 

 pendent origin should be assigned to this small system of 

 volcanic products. 



As the age of the whole system of Banks Peninsula is not 

 yet settled with any exactitude, it would be idle to attempt to 

 ascertain the precise geological age at which this minor erup- 

 tion took place. There is, however, little difficulty in ascer- 

 taining its age relatively to the other eruptions of this volcanic 

 system. 



It is stated by Sir J. von Haast that the original crater 

 was the only one whose eruptions were of a sufficiently spas- 

 modic character to rend fissures in the surrounding rocks, 

 which, on being filled with igneous matter, form dykes. 



