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of Edinburgh, Session 1883 - 84 . 
In another memoir * we have pointed out the distribution of 
these particles on the floor of the ocean, and indicated the conclu- 
sions which we believe are justifled by their relative abundance in 
the red clay areas of the Central Paciflc. 
It is known that the atmosphere holds in suspension an immense 
number of microscopic particles which are of organic and inorganic 
origin, and are either dust taken up by aerial currents from the ground 
or are extra-terrestrial bodies. A large number of scientific men, 
headed by Ehrenberg, Daubree, Reich enbach, Nordenskiold, and 
Tissandier, have studied this interesting problem, and have brought 
forward many facts in support of the cosmic origin of some of the 
metallic particles found in atmospheric precipitations. It is certain 
that serious objections may be raised against the origin of a large 
number of so-called cosmic dusts. 
In a great many cases it can be shown that these dusts are com- 
posed of the same minerals as the terrestrial rocks which are to be 
met with at short distances from the spot where the dust has been 
collected, and we can attribute a cosmic origin only to the metallic 
iron in these dusts. It is somewhat astonishing, however, that 
no trace is ever found in these dusts of meteoric silicates, although 
in a great many meteorites it might be said that the iron is 
only accidentally present, while the silicates predominate. On 
the other hand, having regard to the mineralogical composition 
of meteorites, it appears strange that the so-called cosmic dusts 
should present characters so variable, from the point of view of 
their mineralogical composition, in the different regions where they 
have been collected. It might also be objected that even the iron, 
nickel, and cobalt could come from volcanic rocks in decomposition 
in which these bodies are sometimes present, and this objection 
would seem quite natural, especially in our particular case, when we 
remember the numerous volcanic fragments in decomjoosition on the 
bottom of the sea. Again, according to numerous researches, native 
iron is found, although rarely, in various rocks and sedimentary layers 
of the globe. A reduction of the oxide of iron into metal might also 
be admitted under the influence of organic substances. It might 
still further be objected in opposition to the cosmic origin of the fine 
particles of native iron that they might be carried by aerial currents 
Ptoc. Poy. Soc. Edin. 
