THE
ERUPTION
OF
31
PELÉE
K. No marked alteration in the coast-line or in the height of the land has thus far been noted in the region of the disturbance. There is, on the other hand, strong reason to believe t h a t violent disturbances took place along the oceanic floor near by, even if not necessarily disturbing in marked degree the position of t h a t floor. L. E a c h violent eruption was accompanied b y a vertical displacement, of short duration and with infrequent oscillations, of the sea-level, the surface rising on b o t h the east and the west side of the island about three feet. M. There can be no doubt as to a chorologic relationship existing between the activities of Pelée and the Soufrière of St. Vincent. The Force of the Explosion.—It is hardly possible, except in a very indeterminate way, to establish a comparison between the explosive force which marked the eruption of May 8,1902, and t h a t of other great eruptions whose histories are fairly well known t o us. If the measure of this force is to be read merely from the mechanical work of volcanic decapitation and evisceration, in the amount of solid material t h a t was thrown out, in the height of projection of some of this material, and the concussions to which these projections gave rise, then the eruption of Pelée m a y be thought to stand far down in the scale of volcanic catastrophism, having been surpassed b y P a p a n d a y a n g (1772), Asama-Yama (1783), Skaptar Jökull (1783), Temboro (1815), Coseguina (1835), K r a k a t a o (1883), Tarawera (1886), Bandai-San (1888), and perhaps even by m a n y of the eruptions of Vesuvius, E t n a , and Mauna Loa. The erupted material of Pelée was not particularly large, and probably even considerably less t h a n t h a t thrown out b y the Soufrière on the day preceding. The volcano had been well opened nearly two weeks in advance of the cataclysm, on April 25, and the crater had been throwing out great quantities of ash and lapilli almost unremittingly since t h a t date. At the moment of the 2 0 - 3 0 per cent.; CaO, 6 - 1 0 per cent.; MgO, 2 - 4 per cent., + N O K O, a n d H 0 . This does n o t differ essentially in composition from t h e andesitic rocks which form t h e old stock of t h e volcano, a n d which are so largely d i s t r i b u t e d over t h e island of Martinique. A t r u e cyclic succession of t h e volcanic rocks, following t h e Richthofen view, would seem n o t t o h a v e been here realized, a l t h o u g h it is t r u e t h a t a large p a r t of t h e ejected material was in all likelihood from t h e old stock of t h e volcano. T o this class belong, doubtless, a large p a r t , if n o t practically t h e whole, of t h e ejected ash, m a n y (if n o t m o s t ) of t h e cracked blocks (certainly ejected in solid form) t h a t h a v e been designated bread-crust b o m b s , a n d m u c h of t h e scoriaceous products. T h e notion t h a t volcanic ash is a p r o d u c t , t h r o u g h finer a n d finer t r i t u r a tion, of a fresh or new l a v a — l a v a of t h e period of e r u p t i o n — s e e m s t o find no s u p p o r t from t h e facts presented b y Pelée. Giraud, from a d e t e r m i n a t i o n of a few fossil remains found in t h e tuffs of Trinité a n d Marin (Turritella tornata, also found in t h e Miocene of P a n a m a — Pecten (Amussium) subpleuronectes, a n d Aturia aturi) a n d on o t h e r grounds, assumes t h e earlier volcanic outflows t o h a v e begun in t h e Oligocene, a n d to h a v e been carried t h r o u g h t h e Miocene period (Bull. Soc. Géol. de F r a n c e , Nov. 17, 1902, p. 395; ibid., Feb. 16, 1903, p. 130). I n a fairly extensive collection of fossils t h a t I o b t a i n e d a t Bassignac, near Trinité a t a n elevation of some 70-80 feet a b o v e t h e sea, t h e Miocene facies is well a p p a r e n t , m a n y of the t y p e s being those t h a t are r e p r e s e n t a t i v e of t h e J a m a i c a n a n d Floridian deposits. 2
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