NARRATIVE OF THE CRUISE. 351 



a few feet from the outside, and the rock is massive. The effect of weathering has been 

 to split it up into loose blocks, which lie thickly scattered over the ground enclosed. 

 The whole outside line being constructed of horizontal columns, forms a sort of natural 

 cyclopian wall, much more capable of resisting the degrading influence of the weather 

 than the massive inside ; hence it might be expected that as they always protrude on a 

 hillslope, the rock being disintegrated in the centre would slip down the hill, forming a 

 heap or talus of rubbish below, and overwhelming the wall encircling the lower edge, but 

 at the same time falling away from the wall of the upper edge, which, owing to its columnar 

 structure, is able to keep its fragments together ; and, in fact, this is what was observed. 

 The upper wall of the more distant one, which stands out a prominent object on the 

 summit of the ridge, is over 50 feet high, and presents a perfectly smooth wall face to 

 the outside. As it stretches down the hillslope, which is here, very steep, its height 

 diminishes irregularly until it is lost in the heap of loose stones covering the lower wall 

 and the whole inside. 



The rock is hard and compact, of a light greenish grey colour, with much of the 

 appearance, though without the ring, of phonolite. Near the outside, or in the columnar 

 part, the rock is closer grained than in the centre, and has a distinct cleavage in a plane 

 perpendicular to the length of the columns. It gelatinizes partially with hydrochloric 

 acid, and the solution contains much soda and some sulphuric acid. It is therefore 

 probable that both nepheline and nosean are present. 



Another prominence on this side of the harbour is formed of precisely similar material. 

 It is a round, greenish grey hill covered with phonolitic rock lying about in angular 

 fragments, generally of a size to be easily lifted. The rock is very similar to that of the 

 hills just described ; and it seems to belong to the same class, differing from the others 

 in the complete disappearance of the outside wall, large pieces of which lie scattered 

 on the slope like portions of dislodged masonry. 



It is to be remarked that in neither of these cases was there any distortion in the 

 beds in which the phonolite occurred. The line of junction of the highest one with the 

 augitic rock was very well shown, and specimens were obtained from it. For a few 

 feet from the line of junction the basalt is considerably altered, the large crystals 

 of augite and olivine disappearing as the line of junction is approached. This line is in 

 general quite decided ; there are many angular particles of the phonolite completely 

 surrounded by the basalt, whereas basalt imbedded in phonolite was not observed. 

 Further, the grain of this basalt, in immediate proximity to the junction, is very fine, 

 becoming rapidly coarser, till the basalt at 10 feet from the junction has the porphyritic 

 appearance which it presents at other parts of the hill. These two facts appear to point 

 to the phonolite as being the more ancient of the two, and to the basalt as having flowed 

 round it. There is no necessity for supposing that the portions of these phonolitic 

 masses should be sections of cylinders ; they may equally well be sections of domes. 



