SOUFRIEEE, AND ON A VISIT TO MONTAGNE PELEE, IN 1902. 
513 
which the discharges take as they sweep down the mountain. The avalanche of 
dust rises in this cleft, it tumbles out on its lower or southern lip, where it is 
hemmed in hy walls of rock on all sides but one. We can easily see that these are 
powerful factors in determining the path along which the blast will travel. But it 
has also been stated'' that on the north side of the crater there are visible passages 
descending obliquely through the rocks of the mountain, and it is from these the 
avalanche of sand is launched in a direction which is nearly horizontal. That may 
be so, but even in that case it is not stated that these fissures are above the southern 
lip, or that they can emit blasts inclining downward at an angle of 12 to 20 degrees 
from the horizontal. And if from these fissures the dust-cloud is shot obliquely 
upwards so as to graze the southern rim of the fissure, it still remains to be 
explained why the cloud sinks down again and flows over the surface of the ground, 
refusing to rise in the air and float away as an ordinary cloud would certainly do. 
This, in fact, merely postpones the difficnlties, and does not settle them. Moreover, if 
such an explanation were possible at Pelee, it would have no bearing whatever on the 
eruptions of the Soufriere, as there the crater is a vast bowl about half as deep as it 
is broad ; the black cloud could never have been shot obliquely from tlie bottom of 
this, down the mountain side, but must have risen nearly vertically into the air. 
The explanation proposed by Professor Jaggar t is of a different kind : “ These 
horizontal blasts are not hard to account for, and do not require a horizontal nozzle 
to project them. They are simply the effect of the down blast after the heavy gravel 
has begun to fall, acting against the iipblast from the throat of the volcano, and both 
together deflected and thrown into terrific whirls or tornadoes by the prevailing wind, 
which on Mont Pelee is north-east.” He would, in fact, account for them by the 
resistance which the sand and lapilli falling through the air offered to the ascent of 
subsequent discharges. Mr. E. 0. Hov^ey | has adopted this hypothesis without 
essential modification. 
Bnt, in our opinion, tliis is quite incompetent to explain the iDehavlour of the ifiack 
clouds we saw on the night of the 9th of July. Before the first black cloud arose no 
very great amount of dust had been projected into the air, and the steam clouds were 
drifting steadily westwards before the trade wind towards Precheur. Before and 
after the appearance of the black cloud tlie steam ascended freely and apjDarently 
without hindrance. The black cloud took a different path, and once it had rolled a 
short way down to the mountain there was nothing above it to prevent it rising 
in the air ; but it hugged the surface of the ground so closely that the conclusion was 
inevitable that it flowed down merely because it was too heavy to ascend. 
* ‘American Journal of Science,’ Series IV., vol. xiv., p. 73, 1902. 
t T. A. Jaggar, “ Field Notes of a Geologist in St. Vincent and Martinique,” ‘ Popular Science 
Monthly,’ vol. Ixi., p. 366, 1902. 
I E. 0. Hovey, “ Martinique and St. Vincent: a Preliminary Report,” ‘ Bixll. Amer. Museum Nat. 
Hist.,’ vol. xvi., p. 341. 
VOL. CC.—A. 3 U 
