280 DR. TEMPEST ANDERSON ON THE ERUPTIONS OF THE SOUFRIERE IN 
end of the Wallibu plateau. The line of this upper part of the valley, if prolonged 
to the sea, passes to the north of the Wallibu plateau down the broad valley of the 
Wallibu Dry and Trespe Rivers, and is blocked opposite the east end of that plateau 
by a great deposit of ash, which has deflected the river into its present course 
(Plate 9). Below this obstruction the broad open valley can still be traced as 
described above, while its floor is now occupied by the two small river valleys above 
mentioned, divided by a plateau or ridge often only a few yards wide, and sometimes 
a mere knife edge. It is formed of ash different from and less consolidated than that 
composing the walls of the main valley, and its top is considerably lower than the 
Wallibu plateau. A closer inspection of the Trespe valley (Plate 12, fig. 2), where 
the narrow gorge has been emptied of the 1902 ash, now shows that the north wall 
is much higher than the south, and also formed of older and more consolidated tuff. 
If the sides of the picture were reversed, it might serve as a view in the Wallibu 
Dry River, the higher bank being in this case the Wallibu plateau to the south. It 
is thus clear that these two rivers are an example in a more advanced stage of the 
process which, as described, is now taking place in the ash of 1902 in the ravine above 
mentioned. 
The Wallibu plateau is composed of ash older than that dividing the above two 
small rivers, but still comparatively new, and its flat top and precipitous sides, both 
north and south, proclaim it to be in an early stage of denudation, while the south 
bank of the Wallibu is composed of older tuff and lava, and shows a much more 
mature type of denudation, viz., sloping hills with rounded or ridged tops, and a 
good deal weathered into valleys or gullies. The same description would apply to the 
north face of the plateau, which is precipitous and obviously much less advanced in 
weathering than the slopes of the Soufriere on the opposite side of the valley to 
the north. The mass appears to be the remains of an avalanche or succession of 
avalanches of hot ash poured into the depression between the Soufriere and Morne 
Garu, on an enormously bigger scale than anything formed by recent eruptions. It 
would seem that the present bed of the Wallibu to the south, and the broad valley 
of the Wallibu Dry and Trespe Rivers to the north, are each the enlarged and deeply 
excavated development of the valleys that were formed at the sides of this 
prehistoric avalanche. 
The Fans and Low Plateaux .—The part of the Wallibu district between the sea 
and the Wallibu plateau, and others like it, of comparatively old date, consist of a 
series of low plateaux and fans (Plate 14). These have been formed by a succession 
of discharges from the Soufriere, which are mostly unstratified, and have been partly 
or wholly consolidated into tuffs. They are much dissected by ravines cut by the 
rivers, and the materials brought down by these have formed fans and deltas 
consisting of water-sorted materials. Sometimes the rivers in the earlier stages of 
their cutting through the plateaux have deposited water-sorted beds on their surfaces, 
which are interbedded with those of ash in situ , rendering the structure more 
