•' ^ ' one q/ifte Sandwich group. 1^ 



matter lining the cavities which has become decomposed. At 

 Wahnea some of the most slaggy and scoriform lavas that I saw 

 had a brownish-red colour, passing to cochineal red. 



Tufaceom Lava.^The fourth and last series of volcanic rocks 

 that I noticed, are such as may be classed under the denomination 

 of tufFas. These vary in consistence, from the loose and friable red- 

 dish tuffa of the pari of Anuanu, to the compact beds alternating 

 with a basaltic rock on the sea-shore near Waihea. These last are 

 full of amygdaloidal cavities, containing radiated zeolites. The 

 specimens comprised in this series are Nos. 2. 15, 16, 14, 50, and 

 51. They almost invariably form subordinate beds of greater 

 or less extent in some of the preceding kinds of volcanic rocks. 

 One of the largest of these is at the brink of the pari of Anna- 

 nti, and to this circumstance of geognostic structure is the exist- 

 ence of this pass owing, which forms so remarkable a feature in 

 the physiognomy of the chain Ronahuanui, and which formerly 

 decided the political fate of these islands. In the bed of a 

 stream, at the base of Raala, I observed interposed between 

 dark coloured compact lava a bed of a substance, which, al- 

 though in consistence much resembling tuffa, yet was very differ- 

 ent from it. Some resemblance it had to the peperino of Italy. 

 In a basis saffron-yellow, streaked with gallstone-yellow, were 

 imbedded dark-green harder crystals, apparently of augite. The 

 basis of these tufFas was earth, resemWing much the earth obtain- 

 ed from the decomposition of lava re-agglutinated together into 

 a firm mud. Its colour varied almost in every locality. In 

 some, wood-brown, wood-brown with a yellowish tinge; in others, 

 tile-red. At the pari Anuanu, where it formed so large a mass, 

 it was hght orange-red. Such is a brief outhne of the leading 

 generalities of the volcanic rocks ; let us now sketch, in the 

 same rapid way, the chief characters of the second class of 



1*OCKS tllG 



Coralline Formation.— The best situations for judging of the 

 relations of this formation to the volcanic, are on the north-east 

 and north-west shores of the island. The coral cliffs or reefs, 

 when submerged, form a series of terraces elevated one above 

 another, in proceeding inwards to the interior of the island. 

 The line of these ledges, when under water, can be traced by 

 the successive lines of surf that break upon them in ranges be- 

 hind each other. The space between the last ledge above high 



