ST. VINCENT IN 1902, AND ON A VISIT TO MONTAGNE PELfiE. 
281 
complex, while the fans laid down in the earlier stages of denudation after an 
eruption are dissected by the rivers later on, leaving terraces at one or both sides 
which merge into the plateaux. The plateaux and fans thus pass insensibly one into 
another, but on the whole it will be convenient in this paper to restrict the term 
“ fan ” to the portion over which the river at present habitually flows at intervals, 
and reserve the term “ plateau” for the more completed and generally higher portion 
over which such a flow no longer generally occurs. 
In the eruption of 1902 the incandescent avalanche which came down the Wallibu, 
as soon as it had passed the deep part of the valley, spread like a fan over the 
plateaux to the north and south. To the south it turned round the lower end of the 
Richmond ridge, where it formed, along with water-borne material, a bar at the 
mouth of the Richmond River. This bar still exists, though much washed away. 
The river has cut a sinuous channel through it. The shore of the plateau, which 
in 1902 was sloping,* is now washed away into a steep cliff 30 or 40 feet high. 
There is only a narrow steep beach at its foot. The plateau at a little distance 
from the shore is about 50 feet in height, and the older portion further inland about 
150 feet, or three times as much. 
The fan of the Wallibu in 1902 extended beyond the coast line, and was very 
steep. Gushes of hot mud came down it,f and tended continually to build it up. 
In 1907 it scarcely extended beyond the coast line, and both have receded consider¬ 
ably. The fan is no longer steep, but has only a very gentle slope, as shown in 
Plate 14, which is taken from the plateau just mentioned. The river appears to 
wander frequently about this fan, as it does further up the valley. In March, 1907, 
it flowed at the south side of the fan, close under the above-mentioned cliff, and is 
consequently concealed behind it in the photograph. The avalanche, where it spread 
north towards the Richmond Estate House below the end of the Wallibu plateau, 
was of unequal thickness. This, in a good section on the north bank of the Wallibu 
fan, was from 10 to 20 feet, and, curiously, it was greater nearer the sea coast. The 
section exposed extended in places to below the old surface, and the line was marked 
by the vegetation which was returning in the old soil. 
The plateaux to the north present similar features in the re-excavated river valleys. 
They show good sections of soft tuff, with a capping of new ash, generally from 10 to 
20 , or even more, feet in thickness, and the line of the old surface is here again visible 
by the return of vegetation. Except about the Wallibu House and Works, their 
surface is generally bare and consolidated into a crust. 
The Wallibu Subsidence .—This took place along the shore north of the Wallibu 
and south of Larikai Point. The foreshore to a breadth of about 200 yards and a 
length of above a mile appears to have subsided into' deep water by a sort of sub¬ 
marine landslide, a secondary effect of the earthquakes connected with the eruption. 
* Part I., Plate 24, fig. 1. 
f Part I., Plate 23, fig. 2. 
VOL. CCVIII.—A. 2 O 
