VOLCANIC EKUPTIONS ON MARTINIQUE AND ST. VINCENT. 335 



with ;i tienuMidous volocitv, like the smoke of a collossiil piece of 

 artillery tired heavenward. This shaft goes to a height of tifteen or 

 twenty thousand feet, and then mushrooms out laterally, so as to 

 cover a circle 50 nnles or more in diameter, with a Nolcanic canopy 

 which is as dark as the ))lackest thunder cloud and whii-h shuts out 

 the light of day like a total eclijjse. The projectile force in eruptions 

 of this kind is so great tiiat it throws the black vapor far above the 

 influence of the trade winds, and the advancing edge of the volcanic 

 mantle moves swiftly eastward 2 miles or more above the fleecy trade- 

 wind clouds that are drifting in the opposite direction."'' 



Something of the teri'ifying grandeur of a, great eruption described 

 al)ove is suggested by a sketch forming PI. \. In tlu^ making of such 

 a cohnnn the voliune of water and of comminuted rock reijuired is 

 enormous. The volume of the colunni is in tlie neigliborhood of 

 4,000.000,000 cu])ic feet. 



If 1 per cent of the cohmm is solid matter, it e([uals -io.doo.ooo cubic 

 feet— eipiais 8,000,000 tons. 



If 10 per cent of the colunm is solid matter, it e((uais 400,000.()0() 

 cubic feet— eijuals 30,000,000 tons. 



To be sure, we have no accurate measures, oio' information being 

 almost entirely qualitative; but as such a column as is referred to has 

 l)een o])served to reach a height by estimate of 10.000 feet in two 

 minutes, it may seemingly l)e safely assumed that it rcMiched its full 

 de\elopment in less than five minutes. The coarser of the solid mat- 

 ter first shot out then begins to fall, and the form of the colunm is 

 maintained by new matter dri\en upward from the crater. Thus 

 during eacii five minut»»s of an eruption some 4,000, 000,000 cul)ic feet 

 of debris-laden steam were expelled from the crater. The average 

 duration of such eruptions is not known. l)ut in certain instances the}^ 

 continued for a considerable^ fraction of an hour. During oavh hour 

 that Mont Pelee or La Soufriere was in full blast something like 

 4S, 000, 000. 0(10 cubic feet of dust and stone laden steam were driven 

 out. Only guesses can be made as to the amount of solid matter the 

 steam contained. Shall w^e assume 1 pn- cent or lo per cent^ Most 

 observers would agree, I fancy, not only that the lattei- was nearer 

 the truth than the former estimate, but that the ti'ue measni'e is in 

 excess of the larger of the two. 



The material extruded in a solid condition, as will be shown laO.'r, is 

 fresh lava which came from deep within th(^ earth; but mingled with 

 it are rock fragments that were torn from the Avails of the conduits 

 through which the discharges occurred. The per cent of old la\a 

 among the ejected solids seems to l)e greater on St. Vincent than on 

 Maitinique. In harmony with this is the larger size of the ci'ater of 

 La Soufriere in comparison with that of Mont Pelee. 



The columns of steam of Kennan's type No. 1 thus show that great 

 volumes of rock' are rising from deep within the earth and l)eing blown 



