DEEP-SEA DEPOSITS. 555 



in sliape. This pumice resembled that from Lipari with elongated 

 libers and silky in api)earance. Isolated bits floated on the surface of 

 the sea, partly covered with the marine animals which had fastened 

 themselves on its surface. The frequency of its appearance is easily 

 explained, for the sea receives an enormous quantity of rock fragments 

 of the same nature from many rivers flowing into it; such particularly 

 is the case in New Zealand, in Jai)an, and in South America. 



As is easy to understand, pulverulent material in suspension, coming 

 from eruptions, has also been observed on the high seas. 



Let us add that at various times navigators have remarked on the 

 surface of the sea an accumulation of pumice under the form of a float- 

 ing covering, sometimes so closely adhering and so extensive as to hin- 

 der the progress of ships. Such was the case in July, 1878, in the 

 south of the Pacific Ocean, according to Capt. Turpey, and according 

 to Capt. Harrington in March, 1879. The Challenger, however, did not 

 observe in its passage any rafts of this sort. 



The circumstances which accompanied the eruptic^n of Krakatau or 

 Eakata on the 27th of August, 1883,* are sufficient to account for the 

 abundance of pumice at the bottom of the abyssal regions of the sea. 



At the time of this cataclysm the prodigious abundance of fine parti- 

 cles thrown out was such that the sky was obscured by them. An eye 

 witness relates: "The sun being in mid-heaven, there was no light in 

 the sky nor even a diffuse trace at the horizon, and this horrible night 

 lasted eighteen hours. The ship Loudon was obliged to remain still 

 where it was in view of the peril awaiting it." Some hours later, on the 

 28th of August, 500 kilometers west of the Straits of Sunda, the ship 

 le Salazie met a violent storm, accompanied with lightning and fearful 

 claps of thunder ; after an interval of a few minutes the rain was rei)la('ed 

 for thirty-six hours with sand which blinded the travellers, and soon 

 after that by a white and iuqjalpable dust, composed of pumice, so that 

 at daybreak the sliii) appeared as though covered with snow. 



The important share of fragmentary volcanic ejections in the depths 

 of the sea thus receives an easy explanation as we shall see. 



In regard to volcanoes situated upon continents, the extremely small 

 particles known under the erroneous name of ashes and the little peb- 

 bles, grains, or lapilli, on account of their small size, are often carried 

 by atmospheric currents to considerable distances and a great jiart of 

 them reach the sea where they are finally deposited. The transporta- 

 tion of verj' fine particles has so to speak no limit, both in the air and 

 in water which is in motion. 



In addition to sub-aerial volcanoes, there are some whose opening or 

 crater is submarine, so that the bottom of tlie sea is frequently the 



* Compies Bendus of the Academy of Sciences, 1883; vol. xcvi, p. 1100. ' 



