SOUFRIERE, AND ON A VISIT TO MONTAGNE PELEE, IN 1902. 
5II 
It will be imderstood also that, as a rule, the greater the mass of* material ejected 
the farther the avalanche travels, and the greater is the black cloud which accom¬ 
panies it. On July 9th the first black cloud was small, and soon came to rest; the 
second was much larger, and nearly overwhelmed us. Of course, we could not say 
what was the absolute velocity of either at any point in its course, but certainly the 
second rushed out J^wice as far as the first across the bay. 
Probably the mass is never homogeneous throughout at any point after it has left 
the crater. The heavier solid ingredients must gradually sink to the bottom and 
flow over the ground, while the lighter gases will tend to rise to the surface and to 
dilate laterally. Thus from an early period in its history the cloud will have a heavy 
base, in which the solid particles preponderate, and an upper part lighter, and 
relatively richer in gases. The black cloud covers and envelopes a hot avalanche. 
The surface and sides of the mass are in contact with the air, mix with it, and are 
cooled. Hence those towards whom the cloud is coming may see a black advancing 
front, while when encircled by it they find it incandescent and red hot. That must 
have been the case with the unfortunate inhabitants of the north end of St. Pierre. 
When we keep in mind the composite nature of these discharges, it becomes possible 
for us in some measure to understand the peculiar properties they possess at different 
points in their course and in different stages of their development. When they rise 
from the crater the gases are in a condition of indescribable turmoil, and buoy up the 
vast quantity of hot sand they bear with them. Each solid particle is cushioned on 
gases violently expanding, and the temperature of the whole mass is exceedingly 
high. Hence it seems quite probable that the black cloud rushes upwards, and may 
even shoot some distance into the air and fall back upon the slopes of the mountain 
when its first impulse is spent and its first heat has cooled. We may, at any late, 
believe that the whole mass has then a mobility which it no longer possesses, when, 
by the expansion of the gases, by mixture with the air and by contact with tlie ground, 
its teiiq)erature has been lowered, and the solid matter is beginning to segregate from 
the gaseous, each taking its own course. 
Some such explanation is required to account for the manner in wliicli tlie upper 
part of the black cloud of May 7th surged over the Somma wall which oveilooks the 
crater of the Soufriere, and poured down the north side of the mountain. The same 
cloud in the lower part of the valleys of the Wallibu and Rabaka Rivers was deflected 
by even comparatively slight lidges, and clung helplessly to the bottoms of the 
ravines—that is to say, its lower and heavier part flowed over the ground, for there 
is good evidence that above this there was an enormous mass of black, dust-laden 
vapours which filled the whole mountain valley between the Soufriere and Morne 
Garu, cutting down and sand-blasting the growing trees, tliough the mass of sand it 
left behind was comparatively small. 
We have said that the blast which levelled the walls of the stone-built houses of 
St. Pierre was about as vigorous as tliat of the vSoufriere at equal distances from the 
