98 THE WONDERS OF GEOLOGY. Lect. I. 



splashing of the water, the depositions resemble large cauli- 

 flowers; and on breaking these masses, vegetable impres- 

 sions are often discovered. Numerous thermal springs 

 occupy the valley in the interior of the island, in the 

 midst of which the Geysers are situated ; it is evident that 

 these waters rise from deep crevices, in which they have 

 been heated by volcanic fires. The rivers proceeding from 

 the springs often resemble milk in appearance, owing to the 

 argillaceous bole which they take up in their passage among 

 the siliceous concretions : such are the white rivers of 

 Olassai. Mount Hecla, like all the mountains of Iceland, 

 is entirely covered with snow, and no smoke appears on its 

 summit. Accumulations of rolled masses of obsidian and 

 pumice-stone form a layer on the flanks of the mountain, 

 thirty feet thick; stems and branches of the birch-tree 

 occur in the midst of this bed ; they are the remains of 

 the ancient forests of the island, which the volcanic erup- 

 tions have entirely extirpated.* 



49. Siliceous thermal waters of New Zealand.— The 

 phenomena under review are being effected at the present 

 moment, on a much grander scale, in the volcanic districts 

 of New Zealand. The principal volcanic mountain of that 

 country is Tongariro, which has an elevation of 6200 feet 

 above the level of the sea. Its crater is a quarter of a mile 

 in diameter, and very deep ; the sides are precipitous, and 

 in some places overhanging, and the entire area is always 

 covered with steam. From this crater streams and torrents 

 of boiling water and vapour, highly charged with silex, are 

 constantly issuing forth, and, flowing down the flanks of the 

 mountain in cascades and torrents, empty themselves into 

 lakes near its base, and deposit in their course siliceous 

 sinter in great abundance, incrusting leaves, branches, and 

 other extraneous substances. The whole of the surrounding 



* Bulletin de la SociSte GSologique de France. 



