298 DR. TEMPEST ANDERSON ON THE ERUPTIONS OF THE SOUFRIERE IN 
' 
about 600 metres (1969 feet) above the former level of the crater lake of the Etang 
* 
Sec from which it sprung.* 
This cone or dome appears to have been formed of viscous lava partially or wholly 
solidified in places, and this mixture would be in a condition, by the sudden dis¬ 
engagement of the vapour and the shattering of the partially solidified rock, to give 
rise to, or at any rate take part along with, other discharges from the chimney in the 
formation of the incandescent avalanches and other forms of “ nuees ardentes”! which 
have been observed. The avalanche seen by us certainly contained a number of large 
blocks of a brighter red colour and apparently of a higher temperature than the rest 
of the material in it, and these presumably had come from the dome. Lacroix 
considers that the “ nuees ardentes ” observed by him proceeded from the surface of 
the dome, and especially from a patch on its south-west flank near the base. They 
did not issue from any well-marked crater on its summit. 
The spine itself seems, as we might have expected, to have been formed of very 
similar material to the dome. Lacroix speaks of a carapace, or shell, on its surface, 
which often was detached in flakes (fendillement), disclosing an interior at a high 
temperature which he describes as consisting of porous matter with driblets (bavure) 
of molten lava exuding from the intervals and cracks. Portions were frequently 
detached with the emission of “ nuees ardentes.” There was no great central passage. 
The surface of the spine was scratched and grooved by friction against the walls of the 
volcanic chimney out of which it rose. Its shape at first was angular, but it was almost 
cylindrical in its later stages, probably because the prominences in the chimney were 
gradually worn off, and its diameter was estimated by Lacroix at 150 metres. He 
calculates that if the spine had not undergone any crumbling and falling (ecroulement) 
between November 3, 1902, and July 4, 1903, it would have attained an altitude of at 
least 2200 metres (7218 feet), and the total height of the column extruded must have 
been about 850 metres (2789 feet), or, say, 2800 feet.J The careful measurements 
regularly taken showed that it diminished in height solely by flaking and falling, and 
that at no time did it sink again into the chimney when it had once risen. It appears 
clear, therefore, that both the dome and the spine were formed by molten matter, with 
perhaps some inclusions of blocks torn from the walls of the passage, being forced up 
from below into the volcanic chimney, that this matter was at first sufficiently plastic 
to spread out and form the dome, and that as cooling gradually took place, parts 
solidified and broke up into large blocks, from some of which the vapours escaped 
* These estimates depend on earlier measurements, the accuracy of which cannot be depended upon to 
within a few metres. 
t The term “ Nuees ardentes,” as used by Lacroix, appears to include both the “ Incandescent 
Avalanches” and “Black Clouds” described in Parti. He now prefers the term “Nuee Peleenne” as 
more general. (‘ L’Eruption du Vesuve en Avril 1906,’ p. 12, par A. Lacroix; ‘Revue Gen^rale des 
Sciences des 30 Octobre et 15 Novembre 1906.’) Both Dr. Flett and I prefer our old terminology as more 
precise. 
} Lacroix, ‘ Montagne Pelee,’ p. 132. 
