4A8 NEW ZEALAND. 
. 
are firm like porcelain, and have a pink tinge. Mammillary concre- 
tions of milk-white chalcedony and pendent stalactites also occur here., 
Lake Rotuma is surrounded by a low flat of pumice and earth, and is 
two feet in diameter; and around, there is a deposit which, in some 
places, is soft like chalk, and in others forms porcelain jasper and 
magnesite.* Some of it adheres to the tongue when applied, and is 
used for making pipes. The wonders of this region, as detailed by 
Dr. Dieffenbach, make it of scarcely less interest than the better 
known volcanic geysers of Iceland. 
The siliceous solutions of this region instruct us on this important 
point, that waters highly heated by volcanic action decompose the 
rocks in contact, and take up silica in solution, along probably with 
the alkaline ingredients of the feldspar. ‘This fact aids us in under- 
standing the siliceous character of portions of the argillaceous rock on 
the Bay of Islands, and the numberless siliceous seams in the same 
rock there and elsewhere. The similar effects in the older sedimen- 
tary strata of our globe, and many of the metamorphic changes which 
are described, require no other explanation. That this should be 
fully appreciated, we must consider that submarine eruptions are 
necessarily attended by vast siliceous solutions, far exceeding in ex- 
tent the pools of New Zealand or Iceland; and, moreover, the perme- 
ating waters which enable the rocks to conduct heat from its source, 
have the same faculty of dissolving the silica of the rock, when heated, 
and will deposit it again on cooling. We may believe that this cause 
in its different modes of operation, has been the great agent in meta- 
morphic operations on the globe. . 
New Zealand, through its coal beds and copper veins, promises to 
be a better mining than agricultural region. The geology of the 
islands has been recently much enhanced in interest by the discovery 
of the remains of the gigantic Dinornis, and other birds of remarkable 
characters. On these points we can add nothing from personal ex- 
amination, as our excursions were limited to the vicinity of the Bay 
of Islands. 
* This magnesite is probably a soft, a/wminous material, (instead of magnesian,) pro- 
ceeding from the decomposition of the volcanic rocks by the action of hot gases and 
steam. 
