one of the Sandwich group. 9 



Basaltic Lava. — The volcanic formation might be viewed as 

 consisting of two parts, — the more compact and basaltiform, and 

 the scoriform ; but these, although in the extreme forming very 

 distinct appearances, pass into each other by insensible gradations; 

 the black basaltic compact rocks are generally seen at a small ele- 

 vation above the level of the sea, as on the sea-shore to the west 

 of Waihea, on the north side of the island, and at the entrance 

 of the valley of Anuanu. The more porous and scoriform rocks 

 generally form the higher grounds, such as the lateral ridges 

 descending from the central chains. But this last rule has many 

 noted exceptions, one of the most striking of which is, that, at 

 Waimea, on the north-east coast, where scoriae almost as cellu- 

 lar as pumice are situate nearly at the level of the sea, and un- 

 der more compact rocks of a porphyritic character, having a 

 dark-blue basis, with imbedded crystals of glassy felspar and 

 olivine, associated in the same hand specimen. 



Even the blackest and most compact rocks, when closely exa- 

 mined, are very different from the basalt of the secondary rocks. 

 They have all a certain degree of porosity, however small, and 

 present angular interstices in their mass, giving the idea of their 

 having been formed by agglutination from a semiviscid mass. 

 The following is the series of these rocks that I collected in the 

 order of their similarity to basalt, Nos. 13, 1, 35, 23, 12, 48, 

 49, 11; 40, 33.* The two last form the bond of connection 

 with the next series, the scoriform. The first is undoubtedly 

 the nearest to basalt, both in its external characters and order 

 of superposition, being from a bed on the sea-shore, near Waihea, 

 which runs into the centre of the island. It will be observed, 

 too, that the nearer in the above order these rocks approach 

 No. 13, the darker is their tint, and the freer they are of im- 

 bedded minerals. As we recede, the tint becomes more grey, 

 and we have numerous crystals of glassy felspar, of small size, 

 and grains of olivine, giving to the reck a porphyritic character. 



Arnygdaloidal Lava. — The next series of the volcanic rocks 

 are the arnygdaloidal, under which may be comprehended spe- 

 cimens No. 18, 17, 8, 20, 28, 36, 48, 19, 10, 22, 3, 9. The 

 last connects them with the next series, the scoriform ; the arnyg- 

 daloidal cavities are generally empty, seldom full; their inner 



* These numbers refer to the specimens sent home with the sketch, and 

 now deposited in the Royal Museum of the University of Edinburgh, 



