VOLCANIC CRATERS AND EXPLOSIONS. 
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also the dust was carried into the higher regions of the atmosphere, and 
gave rise to remarkable sunset effects.* * * § The surrounding country for 
many miles was devastated and a large number of lives were lost, but the 
place is so remote that the eruption did not attract the attention it deserved. J 
The ashes in these two last eruptions, and also in that of Tarawera in 
New Zealand in 1886 , are consolidating by time and pressure into tuff, a soft 
porous rock, which by the action of rain and streams shows a characteristic 
feather-like pattern on the surface, and weathers into remarkable ravines, f 
The Tarawera eruption was a fissure eruption, a class which has of 
late attracted much attention. A series of small craters opened along the 
line of a great fissure several miles long, the chief action, however, being 
localized in Lake Tarawera, all the water in which was blown out, and the 
pink and white terraces which formerly existed there were totally destroyed. 
Percy Smith, formerly Surveyor-General of New Zealand, who was one 
of the first party to visit the scene of the eruption, told me that he descended 
500 feet into the crater which opened in the floor of the lake, and which 
is now again filled with water.§ Fissure eruptions are also common in 
Iceland, and are generally accompanied by the discharge of enormous 
volumes of very liquid basalt lava. The historic eruption of the 
Skapta Jokul f in the latter half of the eighteenth century was of this class.]] 
When the early part of an eruption has been explosive, and a cone has 
been built up in the manner described, the magma which rises in the 
volcanic chimney (or vent) tends, towards the end of the eruption, to have 
parted with most of its contained vapour, and the mass often cools and 
solidifies in the form of a plug, which has been supported by the materials 
of the cone, acting as a sort of mould or matrix. If now the soft ashes are 
removed by any of the processes of subaereal denudation, for instance by 
the action of a river, the plug may remain standing and is called a volcanic 
neck.| Such are not uncommon, and good instances occur on the Rhine 
between Bonn and Coblenz, where they consist of columnar basalt, and 
at Le Puy en Yelay in Central France, where the Rocher St. Michel f consists 
of a mass of agglomerate, i.e. angular fragments of volcanic material, 
which had been churned up and down in the chimney while hot and 
finally become coherent. 
A variation of this process has produced the Domitic Puys in Auvergne, 
of which the Grand Sarcoui f is one of the best examples. The lava as it 
issued was so pasty and viscid that it did not run down as a stream, but 
formed a rounded flattened dome between two cones of fragmentary 
materials, one of them very perfect, both of which appear to have been 
formed in the early part of the same eruption. 
* Verbeek, ‘ Krakatau,’ also ‘ Report of Royal Soc. Com.’ 
% T. Anderson, Geographical Journal , 1907. 
f Slide shown. 
§ See his Official Report. 
|| Helland, Lakis Kratere. 
A 2 
