556 iDEEP-SEA. DEiPOSlTS. 



seat of the eruption. Kecent soundings have revealed in tlie Great 

 Ocean the presence of isolated and conical mountains, having the form 

 characteristic of volcanoes and rising from the deep without however 

 reaching the surface. Although circumstances do not favor their obser- 

 vation, submarine eruptions seem to be numerous. In many cases 

 eru})tions are betrayed by sulphurous emanations, columns of vapor, 

 ejections of ashes, scorise, and pumice. Sometimes there appear 

 islands formed of the incoherent debris which disappear later, as has 

 been seen in the Mediterranean, as in the Atlantic — in the neighborhood 

 of the Azores, and in the Pacific Ocean. 



After the eruption of Krakatau an enormous deposit of this incohe- 

 rent matter covered the whole country; its thickness over a radius of 

 15 kilometers was from UO to 40 and sometimes SO meters. Two islands, 

 Stears-Eiland and Calmeyer-Eiland, foruied by these ejections, were 

 thrown up. There was formed also in a few hours an immense floating 

 barrier of pumice, which closed the Bay of Kampong in the Straits of 

 Sunda. The length of the barrier was nearly 30 kilometers by a width 

 of more than 1 kilometer and a depth of 4 to 5 meters, or 150,000,000 

 of cubic meters of i)rojectiles. It could then be seen how the wear and 

 trituration of this friable material rubbing together is effected in the sea. 

 Hitting and rubbing against each other, the stones became round and 

 acquired the form of rolled pebbles, as generally shown in the ])nmice 

 fished or dredged from the ocean. On the other hand, this trituration 

 caused a multitude of very small S[)linters, similar in appearance and in 

 mineralogical composition according to the examination made by Mr. 

 lienard to the pulverized pumice brought up so abundantly bj^ the 

 dredges from the great depths. Mr. Verbeek estimates that the total 

 volume of sand and cinders from this formidable cataclysm reached 18 

 cubic kilometers. Enormous as is this vokime, it was exceeded by that 

 thrown up by Timboro, or Tambora, in 1815, the volume of which was 

 at least, it is said, 150 cubic kilometers. 



The oceanic basins are favorably situated to receive from many 

 points, and quite frequently, volcanic ejections; the general distribu- 

 tion of volcanoes on the surface of the globe explains the considerable 

 part which th<4r ejections occupy in the sea depths. In fact, the largest 

 number of them, about seven-eighths, are situated in the long lineal 

 series which wind about the Pacific Ocean as well as about many islands 

 in that ocean. The circumference of this immense mass of water may 

 be compared to a ring of fire where the volcanic action is scarcely ever 

 interrupted. The Atlantic shows also numerous centers of activity of 

 the same nature, both in the archipelagoes and in the continents which 

 they border. 



It must therefore happen that the small particles, ashes, and lapilH, 

 which are projected from the eru])tive openings of our planet, reach (for 

 the most part), by reason of their fineness, to the great oceans ; if they do 

 not fall directly into them they are carried to them by the currents of 

 air, and often to great distances from the crater whence they issued. 



