April 17, 1884] 



NA TURE 



589 



silica (65 jicr cent.) which our analysis shows appears too high, 

 but if we remember, what we have just said, that the ashes 

 become deprived, during their passage through the atmosphere, 

 of the heavier and more basic elements, it will be understood 

 tltat the vitreous and felspathic materials, which have a lower 

 specific gravity, and are at the same time more acid, will accu- 

 mulate at points farthest from the volcano. It will be sufficient 

 to have directed the attention to this fact to show how the per- 

 centage of silica in the ashes from the same eruption may vary 

 according as they are collected at a variable distance from the 

 crater. 



The predominance of vitreous splinters in deep-sea sediments 

 far remo\'ed from coasts is even more ]5ronounced than in vol- 

 canic aslies collected on land. 1'his arises, as we indicated at 

 the commencement, from the large quantity of pumice carried or 

 projected into the ocean, whose trituration, which takes place so 

 easily, gives origin to vitreous fragments difficult to distinguish 

 from those projected from a volcano in the form of impalpable 

 dust. In addition, we may state that, in the distribution of vol- 

 canic materials on the bottom of the sea, the ashes are subjected to 

 a mode of sorting having some analogy to that which takes place 

 during transport through the atmosphere. W'hen these ashes 

 fall into the sea a separation takes place in the water ; the 

 heaviest particles reach the bottom first, and then the lighter and 

 amaller ones, descending more slowly, are deposited upon the 

 larger and heavier fragments and crystals from the same erup- 

 tion. AVe have a fine example of this stratification of submarine 

 tufa in the centre of the South Pacific, lat. 22° 2l' S., long. 150' 

 17' W. This specimen is entirely covered with peroxide of 

 manganese, and at the base of the fragment we see the large 

 crystals of hornblende and particles of magnetite. This lower 

 layer is covered by a deposit in which these minerals and coarser 

 grains are obsei-ved to pass gradually into a layer composed of 

 small crystals of felspar, debris of pumice, and more or less fine 

 material. 



We do not propose to occupy ourselves here with the mode of 

 formation of volcanic ashes, and with those of Krakatoa in par- 

 ticular. It will suffice to indicate that in the dust of a volcano 

 we find all the characters supporting the interpretation which 

 regards volcanic ashes as formed by the pulverisation of an 

 igneous fluid mass in which float crystals already formed, and 

 from whicli, when projected by gases, the pulverised vitieous 

 particles undergo a rapid cooling and decrepitation during their 

 passage through the atmosphere. It is not only the microscopic 

 examination of these volcanic matters that leads us to this con- 

 clusion, but the prodigious quantity of ashes formed during the 

 eruption of this volcano, which do not agree with the interpreta- 

 tion that regaids these ashes as the result of a pulverisation of a 

 rock already solidified in the crater. Indeed one cannot under- 

 stand how in two or three days the immense quantity of ashes 

 ejected from Krakatoa could be formed by this process, as, for 

 instance, on .August 26, 1S83, and in the May eruption, which 

 was the prelude to that catastrophe. 



Second P.\rt 



The recent brilliant sunsets have been attributed to the pre- 

 sence in the atmosphere of minute particles of an extra-terrestrial 

 origin, as well as to volcanic dust. This induces us to conclude 

 this brief abstract of our observations by a description of the 

 cosmic particles which we have found, along with volcanic ashes 

 and pumice, in those regions of the deep sea far from land, 

 where the sediment accumulates with extreme slowness. In 

 another memoir ' we have pointed out the distribution of these 

 particles on the floor of the ocean, and indicated the conclusions 

 w hich we believe are justified by their relative abundance in the 

 rcil clay areas of the Central Pacific. 



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, 

 Reichenbach, Nordenskjold, 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 

 composed 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 

 tliat the iron is only accidentally present, while the silicates pre- 

 dominate. On the other hand, having regard to the minera- 

 logical 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 would 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 numer- 

 ous volcanic fragments in decomposition 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 from our furnaces, locomotives, the ashes of our 

 grates, and in the case of the ocean, from steamers. All our 

 materials of combustion furnish considerable quantities of iron 

 dust, and it would not be astonishing to find that this, after 

 having been transported by the winds, should again fall on the 

 surface of the earth at great distances from its source. 



Such are the objections which present themselves when it is 

 proposed to pronounce upon the origin of particles which we are 

 inclined to regard as cosmic, and of which we propose here to 

 give a short description. We shall see that many of these doubts 

 are at once removed by a statement of the circumstances under 

 which cosmic spherules are found in deep-sea deposits, and it 

 will be found also that all the objections are disposed of when 

 we show the association of metallic spherules with the most 

 characteristic bodies of undoubted meteorites. 



In the first place, the considerable distance from land at 

 which we find cosmic particles in greatest abundance in deep-sea 

 deposits, eliminates at once objections which might be raised 

 with respect to metallic particles found in the neighbourhood of 

 inhabited countries. On the other hand, the form and character 

 of the spherules of extra-terrestrial origin are essentially different 

 from those collected near manufacturing centres. These mag- 

 netic spherules have never elongated necks or a cracked surface 

 like those derived from furnaces with which we have carefully 

 compared them. Neither are the magnetic spherules with a 

 metallic centre comparable either in their form or structure to 

 those particles of native iron which have been described in the 

 eruptive rocks, especially in the basaltic rocks of the north of 

 Ireland, of Iceland, &c. 



Having referred to the objections, let us now see on what we 

 must rely in support of the hypothesis that many of the magnetic 

 particles from the bottom of the sea which are specially abundant 

 in those regions where the rate of accumulation of the deposit is 

 exceedingly slow are of cosmic origin. If we plunge a magnet 

 into an oceanic deposit, specially a red clay from the central 

 parts of the Pacific, we extract particles, some of which are 

 magnetite from volcanic rocks, and to which vitreous matters are 

 often attached ; others again are quite isolated, and differ in 

 most of their properties from the former. The latter are generally 

 round, measuring hardly o'2 mm., generally they are smaller, 

 their surface is quite covered with a brilliant black coniing 

 having all the properties of magnetic oxide of iron ; often there 

 may be noticed upon them cup-like depressions clearly marked. 

 If we break down these spherules in an agate moitar, the 

 brilliant black coating easily falls away and reveals white or 

 gray metallic malleable nuclei, which may be beaten out by the 

 pestle into thin lamella;. This metallic centre, when treated 

 with an acidulated solution of sulphate of copper, immediately 

 assumes a coppery coat, thus showing that it consists of native 

 iron. But there are some malleable metallic nuclei extracted 

 from the spherules which do not give this reaction, they do not 

 take the copper coating. Chemical reaction shows that they 

 contain cobalt and nickel ; veiy probably they constitute an alloy 

 of iron and these two metals, such as is often found in meteorites, 

 and whose presence in large quantities hinders the production of 

 the coppery coating on the iron. G. Rose has shown that this 

 coating of black oxide of iron is found on the periphery of 

 meteorites of native iron, and its presence is readily understood 

 when we admit their cosmic origin. Indeed these meteoric 



