of Edinhurgh, Session 1883-84. 
475 
those silicates and pyrogenons minerals and rocks, whose microscopic 
characters and distribution at the bottom of the sea we shall 
presently point out. 
During the past few years we have added greatly to the observa- 
tions which were the subject of Mr Murray’s communication. The 
present paper has been suggested by the striking analogy which 
exists between the volcanic products we have found in all deep sea 
sediments and the ashes and incoherent products of a recent cele- 
brated eruption, — that of Krakatoa. The remarkable meteorological 
phenomena we have recently witnessed have been attributed by 
some to the presence in the atmosphere of mineral particles derived 
from this volcanic eruption, and by others to that of cosmic 
dust. It is said that in several places in America, and even in 
Europe, matters have been collected which must be regarded as the 
ashes from Krakatoa, which have been suspended for several months 
in the upper currents of the atmosphere. The importance of this 
matter has been recognised by the Royal Society of London, which 
has appointed a committee of its members to collect all the 
documents and observations relative to the distribution of these 
ashes. The present state of the question induces us to make known 
some results of the detailed researches which we have undertaken 
upon similar subjects. We desire to make known to those who wish 
to study atmospheric dust, the distinctive microscopic characters by 
the aid of which we have been able to establish the volcanic or 
cosmic nature of certain particles found in deep sea deposits, and to 
show at the same time the enormous area of the ocean over which 
we have been able to detect their distribution. 
We believe that no better example could be found in support of 
our interpretations than the microscopic study of the ashes from 
Krakatoa, whose mineralogical and chemical composition M. Eenard * 
was the first to make known, and whose observations on this subject 
have been amply confirmed by the later researches of other minera- 
logists. On the other hand, the conditions under which floating 
pumice was found after that eruption agree perfectly with the inter- 
pretation given eight years ago by Mr Murray, relative to the mode 
of transport of these vitreous matters, and of the accumulation of 
their triturated debris on the bottom of the ocean. We shall also 
* “Les cendres volcaniques de I’eruption du Krakatau” {Bull. Acad. Boy. 
de Belghiue, ser. 3, t, vi. No. 11 Seance du 3 Nov. 1883). 
